Frozen Section of Thyroid and Parathyroid Specimens Rose C. Anton, MD; Thomas M. Wheeler, MD

● Context.—Preoperative fine-needle aspiration of thyroid lesions has greatly diminished the need for surgical evaluation. However, because thyroid nodules are common lesions, many still require surgical intervention and represent a substantial number of cases that the pathologist encounters in the frozen section laboratory. Objective.—Comprehensive reviews of frozen section indications, as well as gross, cytologic, and histologic features of the most common and diagnostically important thyroid and parathyroid lesions, are presented to provide a guideline for proper triage and management of these cases in the frozen section laboratory. The most common pit-

falls are discussed in an attempt to avoid discordant diagnoses. Data Sources.—Thyroid lobectomy, subtotal or total thyroidectomy, and parathyroid biopsy or parathyroidectomy cases are included in this review. Conclusions.—The frozen section evaluation of thyroid and parathyroid lesions remains a highly accurate procedure with a low false-positive rate. Gross inspection, complemented by cytologic and histologic review, provides the surgeon with the rapid, reliable, cost-effective information necessary for optimum patient care. (Arch Pathol Lab Med. 2005;129:1575–1584)

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thyroids to be the fifth most frequent anatomic site with discordant diagnoses, following skin, breast, female genital system, and lymph nodes for metastatic disease.6 This finding becomes even more compelling when observing that lobectomy specimens harboring a well-circumscribed nodule with follicular features were not included as potential discordant diagnoses in the study. The difficulty in performing and interpreting frozen sections of the thyroid gland has prompted some surgeons to dictate their surgical plan based on the results of FNA biopsy, foregoing frozen section altogether.7,8 This approach, combined with the deep-rooted divergent opinions in the surgical community on the appropriate management of thyroid nodules, has resulted in differing approaches to the patient with a thyroid nodule. Although some have called the value of the frozen section into question, the pathologist can still prove to be a valuable asset to the surgical team.

hyroid nodules are common among the general population and often represent a large proportion of endocrine referrals. For a variety of factors, although an estimated 18 400 new thyroid carcinomas were diagnosed in 2000, only 1200 cancer deaths were predicted.1 The incidence of a clinically palpable thyroid nodule is 4% to 7%, and autopsy studies have shown rates of 50% in the general population.2,3 With a malignancy rate of approximately 5% to 20%, this indicates the potential for excessive, unnecessary surgical intervention in a large number of patients.4,5 By the end of the last century, the number of patients requiring surgical evaluation had decreased in large part owing to the acceptance of the highly accurate fine-needle aspiration (FNA) biopsy as the gold standard for initial diagnosis. Fine-needle aspiration biopsy not only helps triage patients into surgical and nonsurgical candidates, but also can guide the extent of surgery. In some cases, frozen section can be avoided altogether, which not only conserves both time and money, but also in cases in which frozen section is still required, provides the pathologist the advantage of knowing initial preoperative cytologic findings that can aid in arriving at the correct frozen section interpretation. Frozen section examination of the thyroid and parathyroids is not as straightforward as it may seem. A College of American Pathologists Q-Probes study of frozen sections from various body sites found the thyroid and para-

THYROID GLAND Types of Specimens

Accepted for publication August 8, 2005. From the Departments of Pathology, The Methodist Hospital, Houston, Tex, and the Weill Medical College of Cornell University, New York, NY (Dr Anton); and the Department of Pathology, Baylor College of Medicine, Houston, Tex (Dr Wheeler). The authors have no relevant financial interest in the products or companies described in this article. Reprints: Rose C. Anton, MD, Department of Pathology, The Methodist Hospital, MS-205, 6565 Fannin St, Houston, TX 77030-2707 (e-mail: [email protected]).

The pathologist usually is asked to examine a thyroid lobectomy specimen grossly or microscopically, with or without isthmusectomy. Lobectomy is generally the preferred treatment of a nodule of uncertain malignancy and represents definitive treatment for benign lesions, including follicular adenoma. Minimally invasive follicular carcinoma is unlikely to metastasize and may be adequately treated with lobectomy, although some surgeons may prefer to undertake a second operation for completion thyroidectomy. A thyroid lobectomy is often received in the frozen section suite with the implication that if a malignant lesion is discovered, a subtotal, near total, total, or completion thyroidectomy will follow. Less commonly, a total or near-total thyroidectomy may represent the initial specimen to be examined. Follicular carcinomas larger than 1.0 cm may be preferably treated initially by com-

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pletion thyroidectomy. Detection of metastatic disease is facilitated by total or near-total thyroidectomy, because residual disease can more easily be identified and ablated by postoperative radioiodine uptake by metastatic tumor. Although multifocal disease is very common in papillary carcinoma, follicular carcinomas are practically never multifocal. Nevertheless, total thyroidectomy eliminates the possibility of disease progression in the contralateral lobe. Total thyroidectomy followed by sodium iodide I 131 scanning and ablation of any remaining areas of uptake has also been shown to decrease recurrence rates.9 Cervical lymph nodes may be sampled with a thyroidectomy specimen in an attempt to establish the presence or absence of metastatic disease and to define the need for a more thorough lymph node dissection. A unilateral lymph node dissection is sometimes included with a total thyroidectomy for papillary carcinoma; however, this is institution dependent and is usually reserved for advanced disease. Cervical lymph nodes are best obtained during the initial surgery for medullary carcinoma for staging and therapeutic purposes. Lymph node sampling is usually not a supplement of surgery for follicular carcinomas, as these tumors metastasize hematogenously to distant sites, most commonly lung and bone. Gross Examination In some ways, gross examination of the thyroid gland at frozen section contributes more pertinent information than does microscopic evaluation. For instance, although papillary carcinomas can demonstrate protean features, ranging from cystic to solid to large infiltrating masses, the presence of a sclerotic, sometimes calcified nodule (Figure 1) or a cystic nodule with recognizable papillary structures (Figure 2) may be seen and is very helpful in arriving at the correct diagnosis. It is as difficult to differentiate benign from malignant follicular lesions at the time of frozen section as it is on preoperative FNA. In fact, studies have confirmed that frozen section provides little added benefit.10–12 However, gross examination of the capsule can be of value in establishing the presence of capsular invasion and circumventing the need for repeat surgery. Some pathologists believe that the presence of capsular invasion is best assessed by gross examination. In addition, carcinomas often will demonstrate a thicker, more irregular capsule than adenomas.13 The distinction of adenomatous nodules from follicular neoplasms can be aided by certain characteristics recognized on gross examination. Hyperplastic nodules are unencapsulated lesions that do not appear to significantly compress adjacent thyroidal tissue. Fibrous strands often subdivide the cut surface into smaller lobules, some of which appear more cellular and solid, while others contain more copious amounts of glistening colloid (Figure 3). Adenomas, on the other hand, are usually single, wellencapsulated lesions that distort and compress adjacent nonneoplastic thyroid (Figure 4). The cut surface is more homogeneously solid without significant amounts of colloid. However, it should be kept in mind that not all lesions with glistening cut surfaces are follicular in origin. The not uncommon follicular variant of papillary carcinoma can easily be confused with a follicular lesion grossly and microscopically, and is a major diagnostic pitfall (Figure 5). Minimally invasive follicular carcinomas resemble adenomas grossly. It is very difficult, if not impossible, to 1576 Arch Pathol Lab Med—Vol 129, December 2005

identify capsular invasion grossly in these lesions. Widely invasive carcinomas, on the other hand, show obvious extracapsular extension by the tumor and, in some cases, no residual capsule can be identified (Figure 6). Anaplastic carcinomas are large tumors that often are seen to infiltrate beyond the capsule of the thyroid into adjacent soft tissues of the neck (Figure 7). It appears that these tumors are associated with preexisting, well-differentiated thyroidal tumors, usually papillary or follicular carcinomas, and a careful search may yield evidence of a simultaneous tumor. Areas of necrosis may sometimes be seen grossly. Medullary carcinomas can vary in size from large and widely invasive, extending into the extrathyroidal soft tissue, to microscopic foci not visible without magnification. Cytologic Interpretation The literature supports the use of intraoperative cytology and frozen section histology as complementary procedures. Similarly, preoperative needle aspiration results should supplement the frozen section examination. Touch imprints or scrape preparations may obtain appreciable cytologic material. Because colloid or cyst contents may be abundant or lesional tissue fibrotic, scrape preparations are sometimes preferable to increase cellularity. The diagnosis of adenomatous nodules and follicular lesions (encompassing cellular adenomatous nodules, follicular adenomas, follicular carcinomas, and follicular variants of papillary carcinomas) is a continuum, with the former demonstrating less cellularity and more copious amounts of colloid and the latter increased cellularity and lesser amounts of colloid. Adenomatous nodules can be diagnosed with confidence using these features. In some cases, if the gross appearance is confirmatory, histologic sections may be omitted altogether, especially if there are multiple, similar-appearing nodules. Lesions with scant colloid and numerous sheets of follicular cells and microfollicles should be evaluated grossly and microscopically to determine if the nodule represents a cellular adenomatous nodule, follicular adenoma, or follicular carcinoma. The follicular nuclei are small, round to oval, and have coarse chromatin and inconspicuous nucleoli. Generally speaking, the mean nuclear area increases from cellular adenomatous nodule to follicular adenoma to follicular carcinoma, although overlapping findings make it difficult to use nuclear size as a predictor in an individual case. Papillary carcinoma and its variants may or may not demonstrate papillary, 3-dimensional, overlapping sheets of cells. Microfollicles may be seen. The key to correctly classifying these tumors as papillary carcinomas, and thereby authorizing completion thyroidectomy, is to recognize powdery fine chromatin, oval nuclei, nuclear holes, and nuclear grooves on cytologic material (Figure 8). Optically clear nuclei, typical in formalin-fixed paraffin sections, are not seen in alcohol-fixed smears or frozen section slides. Psammoma bodies are not usually seen, but when present are helpful. The smears are cellular and there is scant to absent colloid. If present, the colloid is often ropy and demonstrates a hard, ‘‘bubblegum’’-type consistency.14 Smears of medullary carcinoma are usually cellular and demonstrate pleomorphism. The malignant cells range from round to spindle-shaped, and plasmacytoid cells are often apparent (Figure 9). The chromatin has neuroendocrine features with a ‘‘salt-and-pepper’’ pattern. In the Frozen Section of Thyroid and Parathyroid—Anton & Wheeler

Figure 1. Sclerotic nodule of papillary carcinoma on lobectomy. Figure 2. Well-defined papillary structures in a cystic papillary carcinoma. Figure 3. Lobectomy specimen with multinodular goiter. Note the shiny cut surface, indicative of the abundant colloid characteristic of this lesion. Figure 4. Follicular adenomas are usually solitary circumscribed lesions surrounded by a fibrous capsule. The surface appears more solid than an adenomatous nodule. These lesions are best classified as ‘‘follicular lesion, defer to permanent sections’’ at the time of frozen examination, unless obvious capsular invasion is seen. Figure 5. Follicular variant of papillary carcinoma. Note the shiny cut surface. Figure 6. Hemilaryngectomy specimen illustrating extrathyroidal invasion of a follicular carcinoma.

background, acellular material indicative of amyloid may be present and somewhat resembles thick colloid. Anaplastic carcinomas are of 3 types: giant cell, spindle cell, and squamoid. Smears from the latter show characteristic features of squamous differentiation, with hard dense cytoplasm and hyperchromatic angular nuclei. Bizarre, pleomorphic, multinucleated giant cells characterize the giant cell type. Occasionally, smaller mononucleated cells with malignant-appearing nuclei are seen in the

background. The spindle cell type demonstrates pleomorphic spindle cells that might otherwise be sufficient to classify a sarcoma. Most lymphomas of the thyroid occur in older individuals and are of the large B-cell type. Lymphomas may be misinterpreted as anaplastic carcinomas histologically at frozen section because they share similar clinical, gross, and some histologic features. The feature most helpful to the pathologist in allowing proper triage of these cases is

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the recognition of dyshesive cells on intraoperative cytologic material as a characteristic feature of lymphoma.

Figure 7. Total thyroidectomy specimen, including internal jugular vein, of an anaplastic carcinoma. There is invasion into adjacent soft tissues of the neck. Necrosis is present. The lower part of the figure demonstrates a tan-pink, solid nodule representing a follicular adenoma, which may be seen in association with these tumors. Figure 8. Intraoperative cytologic imprint of papillary carcinoma showing fine chromatin, nuclear holes, and nuclear grooves (hematoxylin-eosin, original magnification 3400). Figure 9. Intraoperative cytologic imprint of medullary carcinoma. The cells show a slight degree of nuclear pleomorphism, round to oval nuclei, and a neuroendocrine-type chromatin pattern (hematoxylin-eosin, original magnification 3400).

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Frozen Section Examination Indications. Nodules regarded as potentially malignant should be evaluated microscopically. Features suggestive of malignancy in a nodule include nonfunction on thyroid scan, enlargement while on thyroid hormone treatment, rapid enlargement, associated hoarseness, neck or facial pain, a solitary nodule in a child, a new solitary nodule in an elderly individual, previous head or neck irradiation, presence of cervical lymphadenopathy, and a family history of thyroid or other endocrine disease. The routine use of preoperative FNA biopsy has made the necessity of preemptive surgery obsolete for many of these instances. The much-referenced article by Hamburger and Hamburger15 suggests that needle biopsy can eliminate 99% of all frozen section examinations. The authors indicate that the applicability of frozen section remains for only those cases in which the needle biopsy is nondiagnostic, when a previously unidentified nodule is detected during surgery, or for detection of cervical lymph node metastasis. Although cytology has led to a decreasing role for frozen section, FNA cannot differentiate follicular adenoma from carcinoma and, therefore, cannot help guide the extent of surgery in these cases. A nodule whose initial aspiration cytology is unsatisfactory for evaluation or indeterminate for malignancy should also be sent for gross and/or microscopic interpretation in the frozen section laboratory. Other indications for frozen section are thyroid nodules found at surgery that have not been previously biopsied and to evaluate surgical margin status. Lesions suggestive of medullary carcinoma should be confirmed prior to completion thyroidectomy and possible bilateral anterior compartment lymph node dissection. Many studies indicate that a benign or malignant preoperative FNA biopsy diagnosis precludes the need for frozen section interpretation.16 Citing increased time, cost, and lack of providing additional pertinent information, a study by Chen et al10 concluded that frozen section is not indicated as an adjunct to surgical treatment. Their estimated cost per useful frozen section was $15 000 to $24 000. However, most authors believe frozen section can still be highly informative, especially in cases in which the preoperative FNA is unsatisfactory or suggestive of malignancy/indeterminate.7,17–19 Others recommend continued routine use of frozen section because it demonstrates higher specificity than needle aspiration biopsy and is a better guide to the surgeon.20,21 Literature reports of the accuracy of frozen section of the thyroid have been consistently high, with rates ranging from 90% to 97%.8,15,20,22 However, with the widespread use of FNA, frozen section accuracy has decreased slightly. Needle aspiration of adenomatous nodules and thyroiditis is frequently diagnostic, effectively eliminating the likelihood of surgical intervention and frozen section, which is also relatively straightforward in these lesions. This has enriched the population undergoing surgery with the more difficult follicular neoplasms. The quest to establish the superiority of needle biopsy or frozen section is preempted by recognizing that the purpose of each is fundamentally different. Needle biopsy triages patients into 2 groups: those suitable for surgical intervention and those who may be treated medically. In these cases, a high sensitivity is required and provided by Frozen Section of Thyroid and Parathyroid—Anton & Wheeler

needle aspiration biopsy. Frozen section, however, dictates the extent of surgery and it is here where high specificity is essential to limit the course of surgery. Because of this reluctance to authorize a more extensive surgical procedure, most studies demonstrate no or very low (0.0%– 0.2%) rates of false-positive diagnoses at frozen section.23,24 Regardless of their defined roles, controversy exists concerning the importance of frozen section in cases with reliable needle biopsy diagnoses, resulting in differing approaches to the patient with a thyroid nodule at various institutions. The maxim, however, remains constant: frozen section is applicable and indicated in patients in whom it will have a modifying impact on the surgical procedure. Pitfalls and Artifacts. Frozen section of the thyroid, as in other organs, is limited by sampling and freezing artifact. Freezing artifact is more pervasive in thyroid sections with increased colloid, blood, or adipose tissue, as these represent significant challenges to the pathologist or histotechnologist attempting to obtain a quality section. An acceptable risk taken by the pathologist includes the possibility of missing a minute papillary carcinoma on frozen section. Many cases exist in which a frozen section diagnosis of benign disease is established on a lobectomy, and the following day a microscopic focus of papillary carcinoma elsewhere in the lobe is identified. In a similar manner, only a dominant nodule in multinodular goiter may be sampled at frozen section, but a separate nodule sampled the following day can demonstrate a simultaneous malignant lesion. Histopathology. Papillary carcinomas may not demonstrate obvious papillary formations and instead appear as broad, flat sheets of cells (Figure 10). A trabecular arrangement can be seen. Classic histologic features of papillary carcinoma include enlarged oval nuclei, chromatin clearing, nuclear holes, and nuclear grooves. However, most if not all of these changes become distorted in the freezing process, creating a diagnostic dilemma for the pathologist. Cryostat-prepared sections of nonneoplastic nuclei introduce artifactual nuclear clearing and enlargement, simulating papillary carcinoma, and thus their presence cannot be the crux on which the diagnosis is formed. Similarly, the distortion affects the shape of the nuclei and the false nuclear clearing attributed to the freezing disavows the presence of any nuclear grooves or holes. It becomes necessary for those cases in which the possibility of papillary carcinoma exists that intraoperative touch imprints or scrape preparations be performed to discern and document the characteristic nuclear features. Papillary structures, nuclear enlargement, oval nuclei, nuclear holes and grooves, and occasionally psammoma bodies are more easily and rapidly recognizable on intraoperative cytology than on histologic sections. The medical, surgical, and pathology communities recognize that the distinction of follicular adenoma from carcinoma rests on the identification of angioinvasion or capsular invasion (Figure 11). To provide relevant information to the surgeon in these situations, the entire capsule must be submitted for microscopic examination at the time of frozen section, a tedious and too often nonproductive endeavor. If the nodule is large, the amount of time required to evaluate the capsule at frozen section does not constitute appropriate therapy. Some authors have attempted to sidestep this issue by stating that only 3 sections are required to sufficiently analyze the capsule at frozen sec-

tion.25 While this represents a tentative attempt at initial classification, it does not provide definitive evaluation and some cases of follicular carcinoma will be missed. A study by McHenry et al8 increased the number of blocks submitted for frozen section in an attempt to evaluate the capsule, but found no improvement in detecting capsular invasion. Angioinvasion and capsular penetration by follicular carcinoma are best assessed on permanent histologic sections. Frozen section distorts and collapses blood vessels, resulting in a difficult if not impossible task for the pathologist to locate angioinvasion by the tumor. Entrapment of nonneoplastic follicular epithelium in the capsule simulates capsular invasion by follicular carcinoma. The identification of angioinvasion and capsular invasion has implications not only on surgical management, but also on eventual outcome. Angioinvasion in particular has been cited as a strong independent prognostic indicator.26 Because detecting the presence of angioinvasion and/or capsular invasion has significant prognostic and therapeutic implications, it is really in the patient’s best interest to delay interpretation until the following day. It is appropriate to diagnose these nodules as ‘‘follicular lesion, defer to permanent section’’ at the time of frozen section, in which case the lobectomy represents adequate surgical therapy. Studies have shown that attempting to correctly classify lesions at the time of frozen section rather than deferring diagnosis until permanent sections can be determined by literally a flip of the coin. For cases ultimately classified as follicular carcinomas on permanent histology, 40% of cases were correctly classified as malignant at frozen section, while 43% were classified as benign.24 Similarly, in a study of cases deferred at frozen section, 50% were subsequently classified as malignant and 50% as benign on permanent histology. Even Las Vegas would not take those odds. Cases diagnosed as ‘‘follicular lesion, defer to permanent sections’’ in the frozen section laboratory understandably can provide some angst to the surgeon. After all, repeat surgery, revision of lobectomy, or partial thyroidectomy operations result in increased incidences of complications, including recurrent laryngeal nerve injury and hypoparathyroidism, and patient compliance. However, recognizing the increased time and expense required to evaluate the entire capsule at frozen section, as well as the fact that it is really not in the patient’s best interest to evaluate these factors at frozen section, most surgeons will be willing to accept the minimal delay. Ultimately, the vast majority of these nodules will be benign anyway, and only a very small minority will require a second operation. Preoperative FNA and frozen section of follicular lesions may produce conflicting results, and the surgeon may discuss with the pathologist the appropriate course of surgery. In cases in which FNA biopsy and frozen section provide discordant results, a conservative approach is prudent. In a study by Layfield et al,21 only 9 (5.6%) of 161 patients required repeat surgery using these standards. Hu¨rthle cell neoplasms present a similar diagnostic dilemma to the pathologist in that angioinvasion or capsular invasion must be established to authorize completion thyroidectomy (Figure 12). Hu¨rthle cell lesions behave more aggressively than their follicular counterparts and, therefore, pathologists should more closely scrutinize these cases for the possibility of invasion. Size is an important prognostic indicator. It has been demonstrated that tumors

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Figure 10. Cryostat-prepared section of papillary carcinoma. There is a papillary architectural pattern; however, note the lack of nuclear holes and grooves characteristic of the tumor. These features are too often negated by frozen artifact and should be assessed by cytologic imprints (hematoxylin-eosin, original magnification 3400). Figure 11. Cryostat-prepared section demonstrating capsular invasion in a follicular carcinoma (hematoxylin-eosin, original magnification 320). Figure 12. Hu¨rthle cell adenoma. These tumors characteristically show a mahogany cut surface. Without the presence of obvious capsular or vascular invasion, these tumors are best classified as follicular lesions at the time of frozen section examination.

1.0 cm or smaller have a 17% incidence of cancer, while those larger than 4.0 cm have a 65% incidence (P , .05).27 Another diagnostic dilemma encountered by the pathologist is whether a solitary follicular lesion represents 1580 Arch Pathol Lab Med—Vol 129, December 2005

an adenoma or adenomatous nodule. Helpful features favoring an adenoma include the presence of compression of adjacent nonneoplastic thyroidal parenchyma, a wellformed thick capsule, hypercellularity and decreased amounts of colloid, and uniform histology different than the adjacent nonneoplastic thyroid. Anaplastic carcinomas comprise giant cell, squamoid, and spindle types present in a pure or mixed pattern (Figure 13). The squamoid pattern resembles that of a nonkeratinizing squamous cell carcinoma of various body sites. The spindle type is analogous to a sarcoma in its histology. The giant cell type is the most pleomorphic of the 3 subtypes and consists of multinucleated and occasionally mononucleated large, bizarre cells. All 3 subtypes are widely invasive and show features of a rapidly growing tumor, including necrosis and brisk mitotic activity. Medullary carcinomas grow in solid sheets, nests, or trabeculae and can demonstrate rosette formation. The malignant cells are round to spindle-shaped and show neuroendocrine features. Amorphous, acellular material representing amyloid is usually present in the background. Differential Diagnosis. A major diagnostic pitfall is the differentiation of a follicular variant of papillary carcinoma from a follicular lesion (adenoma or carcinoma). Both tumors are cellular and are composed of small, welldefined follicles with scant colloid (Figure 14). The freezing artifact eliminates the presence of many of the defining features of papillary carcinoma, including nuclear holes, nuclear grooves, and optically clear nuclei. The distinction of papillary carcinoma from follicular lesions has important implications because the appropriate initial treatment of a follicular lesion is simple lobectomy, while a papillary carcinoma of appreciable size requires total thyroidectomy. Preoperative FNA biopsy is also too often unable to accurately classify these lesions. In these cases, frozen section plays an important role. Intraoperative cytologic touch imprints or scrape preparations aid in the recognition of some characteristic features of papillary carcinoma, namely, nuclear holes and grooves. A cellular follicular lesion on frozen section histology whose corresponding imprints show only rare holes and grooves may be interpreted as a follicular lesion on frozen section. However, if sufficient holes and grooves are recognized, then the diagnosis of a follicular variant of papillary carcinoma can be rendered with confidence. The hyalinizing trabecular adenoma deserves special mention because it shares overlapping cytologic features with papillary carcinoma and, if misdiagnosed, results in excessive surgical treatment. These are rare benign tumors that grossly resemble a typical adenoma. The tumor cells, as the name implies, are arranged in trabeculae separated by an extracellular hyaline stroma. The tumors slightly resemble paragangliomas microscopically, with an absence of colloid and a suggestion of zellballen formation. The nuclei are round to oval and demonstrate intranuclear holes and grooves. Acellular fragments of stroma are present in the background but may be easily overlooked. Because of the importance of intraoperative cytologic evaluation in establishing or excluding the diagnosis of papillary carcinoma, the presence of nuclear holes and grooves should raise the possibility of papillary carcinoma. In these cases, it is imperative to review a cryostatprepared section to recognize the trabecular arrangement and hyaline stroma characteristic of a hyalinizing trabecFrozen Section of Thyroid and Parathyroid—Anton & Wheeler

ular adenoma and to correctly indicate that no additional surgical treatment is necessary. Insular carcinoma is another rare tumor, arising from follicular cells (Figure 15). The malignant cells are arranged in nests with curved outlines and are composed of a monotonous population of cells with small round nuclei and high nuclear-cytoplasmic ratios. Scattered microfollicles are seen in the background. Because of their solid growth pattern, they can sometimes be misdiagnosed as anaplastic carcinomas; however, the presence of a monotonous, rather than highly pleomorphic, cell population mitigates against this diagnosis. These tumors are more frequently misinterpreted as medullary carcinomas because the histologic features resemble a neuroendocrine neoplasm. The presence or absence of amyloid is an important distinguishing feature. Whether these tumors are correctly classified as insular carcinomas or as medullary or anaplastic carcinomas has little impact on surgical management, as all are appropriately treated initially with thyroidectomy. Because anaplastic carcinomas are high-grade malignant neoplasms sometimes without obvious better-differentiated areas to suggest the cell of origin, they can easily be confused with other high-grade malignancies involving the thyroid. The spindle cell type can easily be confused with a sarcoma (Figure 16). Although sarcomas of the thyroid do occur, the presence of a high-grade spindle cell tumor, especially in an elderly individual, should raise one’s suspicion for anaplastic carcinoma. If a simultaneous papillary or follicular carcinoma is identified, this lends credence to the diagnosis. Fortunately for the pathologist, the distinction at frozen section is not crucial, as the accepted treatment for both remains total thyroidectomy. Metastatic carcinomas or direct extension from the skin simulates the squamoid variant. Discussion with the surgeon and clinical correlation are necessary to establish the correct diagnosis. Not infrequently, high-grade lymphomas may present a diagnostic pitfall. Both tumors occur most commonly in elderly individuals and are locally aggressive, invading beyond the thyroid into the soft tissues of the neck. Again, whether the correct diagnosis is rendered at frozen section is not essential, as most authors believe the proper surgical management of thyroid lymphomas is total removal of the gland. Optimally, however, proper handling of the specimen at frozen section dictates sampling of fresh tissue for flow cytometric evaluation. In these instances, preparation of intraoperative cytologic material is paramount, because these smears show dyshesion of the malignant cells, at least raising the possibility of lymphoma and alerting the pathologist of the need for subsequent necessary ancillary studies.

which are off-white. Parathyroid adenomas are usually larger than a centimeter, tan to red-brown, circumscribed, and sometimes encapsulated (Figure 17). Occasionally, a thin rim of compressed adjacent nonneoplastic parathyroid tissue can be identified. Cut surfaces may show hemorrhage, fibrosis, or cystic degeneration. Carcinomas are often large and demonstrate extension and adherence to adjacent soft tissue in the neck. The cut surface is tan-gray, hard, and divided into lobules by thick fibrous septa. Cytologic Interpretation Intraoperative touch imprints of parathyroid are invaluable for tissue identification. Too often the pathologist is asked to evaluate a biopsy of tissue smaller than 1 or 2 mm. These miniscule samples can very easily be entirely cut through in tissue processing before a section can be obtained. In these instances, touch preparations obtained before processing serve as a reliable source for evaluation of the submitted tissue. Three cell types comprise parathyroid tissue: chief, oxyphil, and water-clear cells. Chief cells are polyhedral and resemble thyroid follicular cells, but are slightly smaller (Figure 18). Oxyphil cells are indistinguishable from thyroid Hu¨rthle cells. They are larger than chief cells and demonstrate abundant eosinophilic cytoplasm. As the name implies, water-clear cells have clear cytoplasm owing to increased amounts of intracellular glycogen. Touch imprints or scrape preparations demonstrate these cells arranged as cohesive, 3-dimensional cell aggregates. Single cells may be present in the background. Microfollicles may be seen. Anisocytosis is usually present and is not a worrisome feature. Because the cells possess delicate cytoplasm, numerous stripped nuclei may be seen. Although these nuclei may resemble lymphocytes, recognition of the overall cohesive nature of the smears allows one to correctly identify the tissue as parathyroid and not lymphoid in origin (Figure 19). The distinction of parathyroid from thyroid is more difficult; however, follicles and colloidlike material are uncommon in parathyroid specimens.

Normal parathyroid glands measure several millimeters and are tan, as opposed to lymph nodes or thymic tissue,

Frozen Section Examination Indications. The role of the pathologist in parathyroid surgery rests largely on identifying the tissue as parathyroid and distinguishing normal parathyroid from abnormal. The incidence of primary hyperparathyroidism is estimated to be as high as 1 in every 1000 persons, with the vast majority of the cases representing adenoma, a smaller percentage comprising hyperplasia, and extremely rare instances of double-adenoma or carcinoma.28 The distinction between hyperplasia and adenoma is not based on pathologic criteria, but on operative findings; optimally, all parathyroids should be identified. Successful operations have been shown to be strongly associated with experience of the surgeon, with cure rates of 95% to 98% after cervical exploration and identification of all parathyroid glands.29 Biopsy of each parathyroid is not necessary and may lead to postoperative hypoparathyroidism. Definitive treatment of primary hyperparathyroidism rests with the removal of all hyperfunctioning tissue. Recently, some authors have espoused the superiority of intraoperative parathyroid hormone assays over frozen section, as the results of these tests inform the operating surgeon when the hyperfunctioning parathyroid tissue has been removed.29,30 These assays have not gained wide acceptance because they are generally only applicable in cas-

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PARATHYROIDS Types of Specimens The surgical pathologist is usually asked to interpret parathyroid tissue from patients with a clinical history of hypercalcemia. Parathyroid tissue may consist of a biopsy for tissue identification or parathyroidectomy. The pathologist is often further requested to distinguish a ‘‘normal’’ from an ‘‘abnormal’’ gland. Gross Examination

Figure 13. Cryostat-prepared section of anaplastic carcinoma, spindle cell type (hematoxylin-eosin, original magnification 3400). Figure 14. Cryostat-prepared section of follicular variant of papillary carcinoma. The lack of obvious nuclear features of papillary carcinoma is a major diagnostic pitfall of frozen sectioning. Intraoperative cytologic imprints are indispensable in evaluation of these lesions (hematoxylin-eosin, original magnification 3200). 1582 Arch Pathol Lab Med—Vol 129, December 2005

Frozen Section of Thyroid and Parathyroid—Anton & Wheeler

es of adenoma and do not decrease operative time, cost, or error. Occasionally, a parathyroid gland may be inadvertently devascularized during thyroid surgery. In these instances, biopsies of possible parathyroid tissue may be submitted to the frozen section laboratory for tissue confirmation before autotransplantation. Pitfalls and Artifacts. Frozen section remains a highly effective procedure to discern parathyroid from nonparathyroid tissue, with accuracy rates of greater than 99%.31 Frozen section artifact, sampling error, and the inability to distinguish parathyroid from a cellular thyroid nodule are the most common sources for an incorrect frozen section interpretation. Intrathyroidal parathyroids are often difficult to discern from thyroid nodules, especially in cases of nodular thyroid disease. Parathyroids must be differentiated from fat, lymph node, and thyroid. Ice crystals formed during the process of tissue freezing can produce clefts in tissue, resembling stromal fat. In these instances, lymphoid tissue may simulate parathyroid and be misinterpreted. Touch imprints of the tissue obtained prior to freezing will demonstrate cohesive epithelial cells, rather than dyshesive lymphocytes, and help avoid a potential pitfall. Thyroid tissue may contain abundant stromal fat. The absence of colloid and recognizing that tissue in the neck may represent parathyroid are key to the correct interpretation, but this is not often possible at frozen evaluation and must await permanent section. Conversely, parathyroid tissue can demonstrate thyroidization, or the presence of microfollicular structures surrounding colloidlike material (Figure 20). The epithelial cells surrounding the luminal colloidlike material often show oncocytic features, resembling thyroid Hu¨rthle cells. In these instances, the frozen section distinction between parathyroid and thyroid tissue should be deferred until diagnostic immunohistochemical stains (thyroglobulin and parathyroid hormone) can be obtained. If a large amount of fat is present in a parathyroid biopsy, then the inability of the frozen section technique to process the sample may result in a false-negative diagnosis. Intraoperative touch preparations are usually able to provide diagnostic tissue in these situations. Histopathology. The basic histologic feature common to all 3 pathologic processes in the parathyroid (hyperplasia, adenoma, and carcinoma) is hypercellularity of the gland. Of the 3, adenomas are by far the most common. However, if the pathologist receives a biopsy from only 1 parathyroid gland for frozen section interpretation, the diagnosis rendered should be ‘‘hypercellular parathyroid tissue.’’ An adenoma can be diagnosed with confidence if only 1 gland is enlarged and hypercellular. Therefore,

without biopsies from all 4 glands, the pathologist is unable to determine the cellular constituency of the remaining parathyroid glands. A diagnosis of ‘‘hypercellular parathyroid tissue’’ can be further qualified as compatible with an adenoma if the remaining parathyroid glands are small and of normal or low cellularity. Thus, the distinction rests with the operating surgeon and, depending on their surgical judgment, additional biopsies may or may not be submitted to the frozen section laboratory. The parathyroid adenoma on parathyroidectomy consists of hypercellular parathyroid tissue arranged in solid sheets or cords with a trabecular pattern. Occasionally, interspersed adipocytes are seen with the adenoma. Nuclear pleomorphism may be present; however, mitoses, capsular invasion, or vascular invasion mitigate against a benign lesion. Parathyroid carcinomas usually consist of trabeculae of malignant cells separated by thick fibrous bands. The presence of mitotic activity can be appreciated on frozen section and touch imprints and is a feature of parathyroid carcinoma. However, degenerating pyknotic nuclei simulate mitoses on frozen section and a careful search for unequivocal mitoses is required. Extracapsular extension and vascular invasion are also good indicators of malignancy. Nuclear atypia, as mentioned previously, is not a criterion of malignancy and is more likely to be observed in benign adenomas. References 1. Greenlee RT, Murray T, Bolden S, Wingo PA. Cancer statistics, 2000. CA Cancer J Clin. 2000;50:7–33. 2. Mortensen JD, Wollner LB, Bennett WA. Gross and microscopic findings in clinically normal thyroid glands. J Clin Endocrinol Metab. 1955;15:1270–1280. 3. Vander JB, Gaston EA, Dawber TR. The significance of nontoxic thyroid nodules: final report of a 15-year study of the incidence of thyroid malignancy. Ann Intern Med. 1968;69:537–540. 4. Davoudi MM, Yeh KA, Wei JP. Utility of fine-needle aspiration cytology and frozen-section examination in the operative management of thyroid nodules. Am Surg. 1997;63:1084–1090. 5. Gharib H. Fine-needle aspiration biopsy of thyroid nodules: advantages, limitations, and effect. Mayo Clin Proc. 1994;69:44–49. 6. Gephardt GN, Zarbo RJ. Interinstitutional comparison of frozen section consultations: a College of American Pathologists Q-Probes study of 90 538 cases in 461 institutions. Arch Pathol Lab Med. 1996;120:804–809. 7. Hamburger JI, Husain M. Contribution of intraoperative pathology evaluation to surgical management of thyroid nodules. Metab Clin North Am. 1990;19: 509–522. 8. McHenry CR, Raeburn C, Strickland T, Marty JJ. The utility of routine frozen section examination for intraoperative diagnosis of thyroid cancer. Am J Surg. 1996;172:658–661. 9. Emerick GT, Duh QY, Siperstein AE, Burrow GN, Clark OH. Diagnosis, treatment, and outcome of follicular thyroid carcinoma. Cancer. 1993;72:3287– 3295. 10. Chen H, Nicol TL, Udelsman R. Follicular lesions of the thyroid: does frozen section evaluation alter operative management? Ann Surg. 1995;222:101– 106. 11. Mulcahy MM, Cohen JI, Anderson PE, Ditomasso J, Schmidt W. Relative

← Figure 15. An insular carcinoma with a solid cut surface. Thin fibrous strands divide lobules of tumor. Figure 16. Spindle cell variant of anaplastic carcinoma. The elongated nuclei simulate those of a sarcoma (hematoxylin-eosin, original magnification 3200). Figure 17. A parathyroid adenoma with a tan cut surface and lack of encapsulation. Figure 18. Intraoperative cytologic imprint of parathyroid tissue. Chief cells are smaller, reminiscent of thyroid follicular cells, and oxyphil cells demonstrate more abundant cytoplasm (hematoxylin-eosin, original magnification 3400). Figure 19. Numerous chief cells and rare oxyphil cells on intraoperative cytologic imprint. Recognition of areas of cellular cohesion is important in discerning parathyroid cells from lymphocytes (hematoxylin-eosin, original magnification 3400). Figure 20. Cryostat-prepared section of parathyroid tissue arranged in microfollicles surrounding colloidlike material. In some cases, immunohistochemistry is required to definitively assign tissue of origin (hematoxylin-eosin, original magnification 3400). Arch Pathol Lab Med—Vol 129, December 2005

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accuracy of fine-needle aspiration and frozen section in the diagnosis of welldifferentiated thyroid cancer. Laryngoscope. 1998;108:494–496. 12. Udelsman R, Westra WH, Donovan PI, Sohn TA, Cameron JL. Randomized prospective evaluation of frozen-section analysis for follicular neoplasms of the thyroid. Ann Surg. 2001;233:716–722. 13. Rosai J, Carcangiu ML, DeLellis RA. Follicular carcinoma. In: Rosai J, Sobin LH, eds. Tumors of the Thyroid Gland. Washington, DC: Armed Forces Institute of Pathology; 1990:50. Atlas of Tumor Pathology; 3rd series, fascicle 5. 14. Ramzy I. Thyroid and parathyroid glands. In: Ramzy I, ed. Clinical Cytopathology and Aspiration Biopsy. 2nd ed. New York, NY: McGraw-Hill Publishing Co; 2001:375. 15. Hamburger JI, Hamburger SW. Declining role of frozen section in surgical planning for thyroid nodules. Surgery. 1985;98:307–312. 16. McHenry CR, Rosen IB, Walfish PG, Bedard Y. Influence of fine-needle aspiration biopsy and frozen section examination on the management of thyroid cancer. Am J Surg. 1993;166:353–356. 17. Boyd LA, Earnhardt RC, Dunn JT, Frierson HF, Hanks JB. Preoperative evaluation and predictive value of fine-needle aspiration and frozen section of thyroid nodules. J Am Coll Surg. 1998;187:494–502. 18. Chang HY, Lin JD, Chen JF, et al. Correlation of fine needle aspiration cytology and frozen section biopsies in the diagnosis of thyroid nodules. J Clin Pathol. 1997;50:1005–1009. 19. DeMay RM. Frozen section of thyroid? Just say no. Am J Clin Pathol. 1998; 110:423–424. 20. Bugis SP, Young JEM, Archibald SD, Chen VSM. Diagnostic accuracy of fine needle aspiration biopsy versus frozen section in solitary thyroid nodules. Am J Surg. 1986;152:411–416. 21. Layfield LJ, Mohrmann RL, Kopald KH, Giuliano AE. Use of aspiration

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cytology and frozen section examination for management of benign and malignant thyroid nodules. Cancer. 1991;68:130–134. 22. Shaha A, Gleich L, DiMaio T, Jaffe BM. Accuracy and pitfalls of frozen section during thyroid surgery. J Surg Oncol. 1990;44:84–92. 23. Kingston GW, Bugis SP, Davis N. Role of frozen section and clinical parameters in distinguishing benign from malignant follicular neoplasms of the thyroid. Am J Surg. 1992;164:603–605. 24. Neale ML, Delbridge L, Reeve TS, Poole AG. The value of frozen section examination in planning surgery for follicular thyroid neoplasms. Aust N Z J Surg. 1993;63:610–613. 25. Kraemer BB. Frozen section diagnosis and the thyroid. Semin Pathol. 1987; 4:169–189. 26. Brennan MD, Bergstrahl EK, van Heerden JA, McConahey WM. Follicular thyroid cancer treated at the Mayo Clinic, 1946 through 1970: initial manifestations, pathologic findings, therapy, and outcome. Mayo Clin Proc. 1991;66:11– 22. 27. Chen H, Nicol TL, Zeiger MA, et al. Hurthle cell neoplasms of the thyroid: are there factors predictive of malignancy? Ann Surg. 1998;227:542–548. 28. Summers GW. Parathyroid exploration: a review of 125 cases. Arch Otolaryngol Head Neck Surg. 1991;117:1237–1241. 29. Starr FL, DeCresce R, Prinz RA. Use of intraoperative parathyroid hormone measurement does not improve success of bilateral neck exploration for hyperparathyroidism. Arch Surg. 2001;136:536–542. 30. Perrier ND, Ituarte P, Kikuchi S, et al. Intraoperative parathyroid aspiration and parathyroid hormone assay as an alternative to frozen section for tissue identification. World J Surg. 2000;24:1319–1322. 31. Westra WH, Pritchett DD, Udelsman R. Intraoperative confirmation of parathyroid tissue during parathyroid exploration: a retrospective evaluation of the frozen section. Am J Surg Pathol. 1998;22:538–544.

Frozen Section of Thyroid and Parathyroid—Anton & Wheeler