1187

Transrectal Sonography Benign and Malignant Prostatic Lesions

L Deland

D.

2

Leo F. Drolshagen1 Arthur

C. FleiScher1 Hal T. Liddell3 w. Scott McDougal3 Edward M. Karl4 A. Everette James, Jr.1

.

of

..

,.

Using linear-array transrectal prostate sonography, malignant lesions in 43 patients and benign lesions in 74 patients were evaluated. Prostate sonography was sensitive to textural changes produced by both benign and malignant diseases. However, there was considerable overlap in the sonographic appearances of benign and malignant lesions, and there were no sonographic features that reliably predicted malignancy. Hyperechoic areas were present in 58% of the carcinomas, while 19% were purely hypoechoic. Lesions containing hypoechoic foci that were posterior or posterolateral had a high incidence of cancer. The resufts confirm the need to biopsy all suspicious palpable lesions of the prostate.

Transrectal prostatic sonography has been shown to be sensitive to textural changes produced by both benign and malignant disease, but no sonographic feature or features within the gland has been found to be accurate in predicting cancer [1 -7]. Most reports characterizing prostate lesions by transrectal sonography are based on transverse images of the prostate obtained with a radial scanner [1 , 5-7]. As yet, there have been only a few reports of sonographic features using a linear array probe [2-4]. In addition, as previously noted by Rifkin et al. [2], most studies have assumed the sonographically abnormal area to be the histologically abnormal area, without direct evidence that the biopsied area actually corresponded to the abnormal region identified by sonography. Rifkin et al., using a real-time linear array probe, obtained direct sonographichistologic correlation by performing prostate biopsies using sonographic guidance or by correlating images with results of prostatic resection [2]. In their study they noted a moderate degree of overlap between the sonographic features of benign and malignant disease. However, the authors reported certain features to be highly suggestive of benign disease, including (1) purely hypoechoic areas; (2) hyperechoic foci that are more echoic than the capsule and greater than 4 mm thick; and (3) foci with shadowing. Twenty cancers were hyperechoic; the other six had mixed October 22, 1985; accepted vision January 23, 1986. Received

1

Department

ences, Vanderbllt villa, TN 37232. FleiSCher. 2

Present

after re-

of Radiology and Radiological Sdlkiiversity Medical Center, NashAddress

address:

reprint

requests

Materials Department

of Surgery, Center, Nashville, TN 4 Department of Pathology, Medical Center, Nashville, TN Department

Medical

AJR

146:1187-1191,

The purpose of this report who had sonographic-pathlogic

June

vanderbilt

1986

0361 -803X/86/1466--1 187 © American Roentgen Ray Society

and illustrate of prostatic

the findings lesions.

in 1 1 7 patients

and

Methods

of Radiology,

Vanderbilt 37232. 37232.

is to describe correlation

to A. C.

January

Between

Navy Hospital, Corpus Christi, TX 78419. 3

echogenicity.

University University

patients

in whom

guided transperineal the 1 17 patients,

1 984 and

histologic

August

correlation

1 985, was

1 1 7 prostate

subsequently

sonograms obtained,

were

either

performed

on

by sonographically

biopsy (1 01 patients) or transurethral prostatectomy (1 6 patients). Of 43 had a histologic diagnosis of adenocarcinoma. The remaining 74 had

benign disease,

predominantly benign prostatic hyperplasia (BPH). Twelve of the cancer patients subsequently underwent radical prostatectomy. Six additional patients had pelvic lymphadenectomy without prostatectomy, five of whom had positive lymph nodes; one other patient

was

discovered

to have

periprostatic

invasion

at operation.

Overall,

three

patients

1188

BURKS

were found to be stage A; 1 8 patients, stage B; nine patients, stage C; and 1 3 patients, stage 0. Sonography was performed using a Toshiba 5055 5-MHz, longitudinally

oriented,

linear-array

transrectal

probe

designed

Toshiba SAL32A linear-array unit (Tustin, nique was similar to that previously described rectal

examination

was

performed

to identify

the

location

of any

palpable lesions, the probe was inserted and the entire prostate gland imaged by first identifying the anatomic midline, as evidenced by the presence of the prostatic urethra, then rotating the probe clockwise and counterclockwise to image the lateral lobes. Representative freeze-frame images from midline and at 5#{176} to 10#{176} increments laterally were recorded on Polaroid 667 film (Cambridge, MA). We preferred, but did not always

bladder.

require,

One hundred

that

the patient

and one patients

transperineal

biopsy

of the

Trucut biopsy

needle

(Travenol,

be scanned

with

had sonographically

prostate

with

performed

Morrow,

guided

a 16-gauge

GA).

genicity

was

predominant

Isoechoic hypoechoic

diffuse different disease,

or cysts and (6) presence estimated

relative

echogenicity

lesions

could

rim or “halo,”

enlargement,

to normal,

of the peripheral

be identified surrounding

of prostatic which

was

generally

the

gland.

either by a surrounding

or focal asymmetry.

thin

June 1986

Features in the Benign and Malignant

Groups M (N

characteristic

=

125)

(N

No. of sites (%)

=

43)

No. of sites (%)

Echogenicity Hyperechoic Isoechoic

38 (30) [55]

5 (1 2) [58J

40 (32)[56J

2 (5)[51]

Hypoechoic

11 (8) [24J 36 (28) 7 (6)

8 (19) [58] 28 (65) 1 (2) 1 1 (25) 8(19) 8 (19)

Mixed Hyper/Hypo/lso

17 (14)

Hyper/Iso

Hyper/Hypo Hype/Iso

6 (5) 6 (5)

Margin Well defined Poorly defined

81 (65) 43 (35)

9 (22) 34 (78)

89 (71) 36 (29)

1 5(35) 28 (65)

Homogeneity Homogeneous

Inhomogeneous Halo

19(14)

Dilated glands or cysts

11

3(7)

(8)b

4 (9)

24 (32)b 15 (2O)b

16(37) 9 (21)

Calculi foci (4 mm and with shadowing)

Echogenic

calculi. Echo-

zone of the prostate hyper-

1 : Sonographic

TABLE

a full

The area of the biopsy or transurethral resection of the prostate was correlated with the histologic diagnosis of either malignancy or benignancy and the lesion was characterized with regard to the following sonographic features: (1) echogenicity, (2) definition of the margins, (3) textural homogeneity, (4) presence or absence of a thin hypoechoic rim or “halo” around the abnormal focus, (5) presence of

dilated glands

AJR:i46,

AL.

for use with

CA). Scanning tech[2, 3]. After a digital

the

ET

m brackets

a

echogenicity

is obtaned

by adding

the components

of the

lesions. For example, 30% of the benign lesions we essentily

mixed

purely hyper-

echoic whereas 55% contan hyperechoty. b is relative to 74 rather than 125.

or hypo-echogenicity,

One hundred

and three

benign sites were analyzed in the 74 patients with benign and only the malignant site was analyzed in the 43 patients

with malignancy. No attempt was made to prospectively presence or absence of cancer.

predict the

In order to obtain direct sonographic-pathologic correlation, specimen sonograms were performed on six consecutive radical prostatectomy specimens containing cancer. Specimens were immersed in saline and scanned with a 7.5-MHz real-time sector probe (Diasonics 400 DRF, Milpitas, CA), and images were recorded on a multiformat camera. The specimens were imaged in both transverse and longi-

tudinal planes. The prostate gland was systematically sectioned for comparison with the images so as to map out the exact extent of the cancer.

Results This prostate gland in all of the patients had some alteration from normal homogeneous, low-level echogenicity [2]. Table 1 summarizes the sonographic features for the lesions. There was considerable overlap of sonographic charactenstics of benign and malignant lesions. Mixed echogenicity, which could be almost any combination of hyper-, hypo-, and iso-echogenicity, was the most common pattern in cancer (65%), but represented only 28% of the benign conditions. This is indirectly reflected in the greater homogeneity seen in BPH lesions. Hyperechogenicity was present in 55% of benign lesions and 58% of malignant lesions when considering the components of the mixed lesions. However, hypoechogenicity was much less frequent in benign disease (24%) than in malignant disease (58%). There was also a notable difference in the location of the hypoechoic lesions between the benign and malignant groups. In the cancer group, most (58%) were posterior or posterolateral, with the

rest (42%) being anterosupenor. Only 1 8% of the hypoechoic lesions in the benign group were posterior or posterolateral. Overall, lesion margins were definable in 65% of the benign group, whereas only 22% were definable in the malignant group. The margin of the lesion within the gland was analyzed. The best definition of a lesion was obtained in nodules surrounded by a thin hypoechoic rim or “halo”; however, this was seen in only a minority of the lesions. Margins of a lesion, when

definable,

were

usually

delineated

by a change

in ech-

ogenicity. Decisions concerning the extent of a lesion were subjective and varied significantly from one observer to another. To a large extent, the homogeneity of a lesion paralleled the delineation of a lesion; the more inhomogeneous, the more indistinct were the margins. Eighty-nine percent of benign lesions were homogeneous, whereas only 20% of malignant lesions were homogeneous. A thin hypoechoic rim or “halo,” a feature not previously described in prostate nodules, was observed in 1 9 of the benign nodules. To be considered a halo, the rim had to be completely circumferential (Fig. 1). Three malignant nodules were

encountered

with

what

could

be considered

a halo,

although one had a much thicker rim than that typical of those encountered in benign lesions. Dilated prostatic glands or cysts are frequently seen microscopically. On sonography, these were identified in 1 2 of the 74 patients with benign disease and in four of the 43 patients with cancer. Even in the glands with cancer, the dilated glands were

in benign

a malignant Punctate,

areas;

however,

one cyst was

focus and contained bloody fluid. brightly echogenic foci, presumably

definitely

within

correspond-

TRANSRECTAL

AJR:146, June 1986

SONOGRAPHY

OF

PROSTATIC

LESIONS

1189

Fig. 2.-Sonogram showing thick, echogenic focus (open arrows) with shadowing possibly due to calcification. Surrounding hypoechoic area (closed arrows) was cancer. Sagittal plane. SP = symphisis publs, B = bladder.

Fig. 1 .-Sonogram ing slightly hyperechoic =

seminal

showing thin hypoechoic rim or “halo” (arrows) surroundBPH nodule. Sagittal plane. SP = symphisis pubis, SV

vesicle.

ing to corpora amylacea deposits or areas of calcification, were frequently seen in both benign and malignant lesions. We specifically analyzed for the presence or absence of thick (>4 mm), brightly echogenic (equal to or greater than the surrounding periprostatic tissue) foci with and without shadowing. In the cancer group, only those foci within or in close proximity to the cancer were included (Fig. 2). Because of the frequent difficulty in defining the extent of the cancer, it was often difficult to ascertain whether the foci were actually within or just adjacent to the cancer. Sixteen (37%) glands in the cancer group had thick, brightly echogenic foci, nine of which had shadowing. Twenty-four (32%) were identified in the benign group, 1 5 of which had shadowing. The foci may well be due to benign material, but they are certainly not an indication that the adjacent or surrounding glandular tissue is benign.

Benign

Prostatic

Hyperplasia

(BPH)

Typically in hyperplasia there was symmetric enlargement of the gland and the gland assumed a more rounded configuration than normal. In the majority of cases, discrete nodules could be identified, some with a “nodule within a nodule” appearance. Nodule echogenicity was most frequently hyperechoic or isoechoic and was least often hypoechoic. Inhomogeneous nodules were not uncommon. Distinction between the hyperplastic central periurethral glands and the compressed peripheral glands was often possible. The peripheral

zone usually had lower echogenicity relative to the centrally located BPH, but some also have greater echogenicity (Fig. 3). Prostatic calculi, identified as bright echogenic foci that were either solitary or clustered, were frequent. These were located anywhere within the gland, but were uncommon in the posterior peripheral gland. They were usually located in two areas: (1) arranged in an arc or ring around BPH nodules, usually between the central and peripheral gland, and (2) periurethral. Prostate margins were generally smooth.

Carcinoma BPH frequently coexisted with cancer; thus the size of the gland ranged from small to markedly enlarged. Most cancers (72%) were located posteriorly or posterolaterally. Diffuse cancers (21 %) usually had a significant posterior component. The remaining cancers were anterosuperior. Cancer foci most often had mixed echogenicity, frequently with a significant hypoechoic component (Fig. 4). When the hypoechoic component of a lesion was within the peripheral zone of the gland (posterior or lateral), it was highly suggestive of cancer. Purely hypoechoic lesions were not uncommon and, when posterior or posterolateral, were highly suggestive of cancer. Asymmetry of the gland was usually not apparent with the linear array

probe,

were

as frequent

benign

but

was

helpful

when

in the gland

with

identified.

cancer

Prostatic

as in those

calculi

with

disease.

In Vitro Study

of Prostatic

Carcinomas

Pathologic analysis of the six prostatectomy specimens demonstrated good correlation between the location of the bulk of the tumor in the specimen with the abnormality on the sonogram. Pathologically, the tumor was usually slightly more extensive than predicted by sonography because of micro-

1190

BURKS

showing BPH, all in sagittal plane. SP = symphisis vesicle. A, WelI.defined, fairly homogeneous, hyperechoic nodule (arrows). B, Central BPH (dashed line). Lesion is composed of multiple nodules that are both hyperechoic and have a nodule-within-a-nodule appearance. Dilated glands are evident at the superiormargin(arrowheads). Peripheral Fig. 3.-Sonograms

pubis, sv

=

seminai

ET

AJR:146, June 1986

AL.

arrows) has slightly greater echogenicity than adjacent central BPH. C, Homogeneous central BPH. Peripheral zone is slightly less echogenic. Small echogenic foci are present (arrowheads), presumably caused by corpora

zone (straight

am.

compensation

or recording medium accounted for the hypoof these carcinomas observed in vivo.

echoic appearance Discussion

Our results expand the spectrum of sonographic appearances of carcinoma beyond those described by Rifkin et al., who reported no hypoechoic cancers and indicated thick, brightly echogenic foci and shadowing to be highly suggestive of benignancy [2]. In our series, hypoechogenicity was a frequent

finding

in cancer

(58%).

If a hypoechoic

lesion

was

posterior

or posterolateral in the peripheral zone, the most common site for cancer to develop, it was highly suggestive of cancer [8], but if it was elsewhere, such as central, it was more likely to represent benign disease. Purely hypoechoic

cancers

were

not uncommon.

Others

have

reported

hypoech-

oic cancers, but they used either transabdominal sonography or a radial scanner and they lacked direct sonographic histologic correlation [5, 9]. In addition, we found that thick, brightly echogenic foci with or without shadowing within or adjacent to a lesion did not exclude cancer. Because of the infiltrating nature of prostate carcinoma, a carcinoma may encompass calculi or develop in close proximity to calculi. Prostate carcinoma may also produce corpora amylacea. Fig. 4.-Carcinoma with mixed echogenicity. Lesion is posterior. There is a hyperechoic area (closed arrows) within a large hypoechoic area (open arrows). Exact extent ofcancer is difficult to define. SP = symphisis publs, B = bladder.

scopic infiltration at the periphery. All of the the six specimens had a hypoechoic area on sonogram (5 MHz) and the in vitro sonogram 5). This finding suggests that it is unlikely

cancers within both the in vivo (7.5 MHz) (Fig. that faulty gain

Our results,

using

linear-array

transducers,

indicate

consid-

erable overlap in the sonographic features between benign and malignant disease; however, some investigators, using radial scanners, have reported a high degree of accuracy. Brooman et al. [1 ] reported 96% overall accuracy, and Harada et al. [5] reported 89% overall accuracy. Rifkin, in a comparison of linear array and radial scanners, found the radial scanner to more clearly define asymmetry and capsular ex-

MR:146,

June 1986

TRANSRECTAL

SONOGRAPHY

Fig. 5.-A, Purely hypoechoic cancer. Sagittal plane. Small tumor is in the peripheral zone posteriotiy (arrows). There is central BPH. SP = symphisis pubis, SV = seminal vesicle. B, Specimen sonogram of same prostate as in 5A but in a transverse orientation using a 7.5-MHz sector probe with a water-path offset, scanned from its posterior aspect. Prostate margins are identified by

tension [1 0], a finding that is supported by our experience with specimen sonograms. Asymmetry in our series was easily detected on specimen sonograms performed in the transverse plane, but was difficult to discern on longitudinally oriented images. Although a technique for precise needle placement in the prostate for biopsy has been described for radial scanners [1 1], the longitudinal orientation and real-time capability of the linear-array probe make it more versatile in biopsy guidance. Prostate biopsy guidance is perhaps the most significant role of transrectal sonography at its present stage of development [10, 12].

In summary, although certain sonographic features may be more suggestive of benign or malignant disease, there are no specific features for either. Thus biopsy of all suspicious palpable lesions of the prostate gland is required. ACKNOWLEDGMENTS

The authors thank the Toshiba Corporation for the use of the equipment that made this study possible. We also thank Monica Harper for preparation of the manuscript and John Bobbitt for photographic assistance. We appreciate the efforts of the urology staff and house staff for referral of the patients. Drs. Linza Killion and Randall Falk are especially thanked for their contributions to this study. REFERENCES

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OF

PROSTATIC

LESIONS

open arrows. Hypoechoic gross specimen obtained

cancer

1191

(closed arrows). C, Corresponding transverse plane and sectioned at approximately the same level as the sonogram. The cancer(straight arrows) is located in the peripheral zone. lkethra (curved arrow) and hyperplastic central tissue is identified

in the

are demonstrated.

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1981;32:669-676

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evaluation

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Real-time ultrasound-guided prostatic biopsy using a new transrectal linear-array probe. Radiology 1983;146:547-548