Evaluation of the prostate by magnetic resonance imaging

Magnc?ic Resonance Imaging, Vol. 4, pp. Printed in the USA. All rights resctwd.

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1986

??Original Contribution EVALUATION OF THE PROSTATE BY MAGNETIC RESONANCE IMAGING BRIAN T. LARKIN, M.D., THOMAS H. BERQUIST, M.D. AND DAVID C. UTZ, M.D. Department of Diagnostic Radiology and of Urology, Mayo Clinic and Mayo Foundation, 200 First Street SW, Rochester, Minnesota 55905, USA Forty-sevenmale patieuts wItbsuspected prostatic disease underwentmagnetic resonanceimaging (MRI)of tke pelvis on a Picker resIstbe maguet Ftiag at 0.15 T, 33 kad histologically proved adenocarciuoma, 12 kenIgnprustatic hypertrophy, 1 a transitional cell carcinoma, and 1 a seminoma. Eleven normal subjects also were inckuied in tke study. Tke study attempted to (1) define tke MRI characteristics of the normal prostate, keuign prostatic byperbopby, aad prostatic adenocarcinomp, (2) evaluate various pulse sequencesin imaging the prostate, aud (3) compare MRI lindings with cIiuical, patkologiq and computed tomograpky results. Various pulse sequences, includinginversion recoveryand spin-echo with skort and long TE and TR, were used. MRI was sensitive in detecting intracapsular aad extracapsular prostatic disease. Tke Rndingof inhomogeneoussignal texture tIuouglmut tke gland was a sensitive but nouspe&ic llndingfor adeuucarcinoma.A focal nodule with prolongedT, aad T2relaxation times was tke most specific MRI tlnding for adenocarckuuua.Extracapsular spread of neoplasm was often demonstrated, and kecause of its superior soft-tissue contrast ability, MRI was more accurate tkan computed tomography in delineatingextracapsular extension. Keywords: Prostate adenocarcinoma, Benign prostatic hypertrophy, MRI, Cf, T,, T2 relaxAo~~ timq PII& sequence.

INTRODUCTION Prostatic changes are universal in aging males. Benign prostatic hypertrophy generally has its onset during the fifth decade of life and is present to some degree in nearly all elderly males. It is characterized by a periurethral glandular proliferation which may lead to urinary tract obstruction. Adenocarcinoma is the second most frequent prostatic disease in males and is the third leading cause of death from cancer in males” (25,000 deaths in 1985). Computed tomography (CT) and ultrasound currently have a limited role in the evaluation of the prostate.7-10 CT often can detect extracapsular extention of neoplasm, adenopathy, and bony metastasis; however, it is less effective in detecting neoplasm confined to the prostate gland.’ Ultrasound often can detect intraglandular changes but is limited in demonstrating extracapsular extent. Magnetic resonance imaging (MRI) offers a new potential in demonstrating both the intraglandular and the extraglandular extent of the neoplasm. RECEIVED9/23/H;

PATIENTS AND METHODS Forty-seven males (age range 48-77 years) with suspected prostate disease were referred for MRI. Eleven subjects (age range 26-75 years) with clinically benign prostates also underwent MRI. MRI of the pelvis was performed using a Picker resistive magnet operating at 0.15 T. T,- and T,weighted images were obtained using spin-echo TE 40, TR 500 and TE 60, TR 20002 and inversion recovery T, 500, TE 40, TR 2,000. Images were obtained in the axial plane and supplemented as needed with sagittal and coronal images. CT scans were obtained in 15 patients. In these patients, MRI was compared with CT in terms of detection of lesions and determination of extent of lesions. MRI findings were correlated with pathologic (biopsy/prostatectomy) findings. RESULTS Normal (Benign) Prostate

The normal prostate was characterized by a relatively uniform medium-intensity signal using various

ACCEPTED10/2/85.

H. Berquist, M.D., Department of Diagnostic Radiology, Mayo Clinic and Mayo Foundation, 200 First Street SW, Rochester, Minnesota 55905.

Presented at the meeting of the Society for Magnetic Resonance Imaging, San Diego, March 22-26, 1985. Address correspondence and reprint requests to Thomas 53

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Magnetic Resonance Imaging 0 Volume 4, Number 1, 1986

IR and SE sequences (Fig. 1). Distinct fascial planes separated the normal-size prostate from the bladder, seminal vesicles, levator ani, and rectum.5 Anteriorly, the retropubic fat in the space of Retzius clearly separated the prostate from the symphysis pubis. Because of the excellent soft-tissue contrast, MRI usually can delineate the periprostatic fibrovascular connective tissue that lies between the microscopic true prostatic capsule (which is not seen with MRI) from the levator ani muscle.’ This fibrovascular stroma could be identified in most of our subjects with a benign prostate. With increasing Tz-weighted sequences, such as increasing TE from 30 to 60 ms and TR from 500 to 2000 ms, an increase in signal intensity was noted in the prostate and seminal vesicles, making accurate delineation of these structures from the surrounding fat more difficult (Fig. 2). Benign Prostatic Hypertrophy In all 12 patients with histologically confirmed benign prostatic hypertrophy, MRI showed gland

Fig. 2. (A) Inversion recovery T,-weighted image (TI 500, TE 40, TR 2,000). Left seminal vesicle (arrow) is well demonstrated and separated from surrounding structures by distinct fascial planes. (B) Spin-echo T,-weighted image in the same patient at the same level (TE 30, TR 2000). Seminal vesicles give a higher signal intensity and are difficult to differentiate from the surrounding fat.

enlargement with preservation of the periprostatic fascial planes (Fig. 3). In the 12 patients, a significant finding was that signal intensity of the prostate parenchyma varied from relatively homogeneous to markedly inhomogeneous (Fig. 4). An inhomogeneous signal texture from the prostate parenchyma was noted in 5 of the 12 patients. A focal intraparenchymal nodule of prolonged T, and T2 relaxation times was not found in any of the 12 patients with benign prostatic hypertrophy.

Fig. 1. (A) Axial spin-echo scan through a clinically normal prostate (TE 40, TR 500). Prostate parenchyma gives a relatively homogeneous signal intensity. Note the high-intensity retropubic fat and low-intensity air within the rectum, obterator internus, and levator ani muscles. (B) Sagittal spin-echo scan through the normal prostate (TE 40, TR 500).

Prostatic Adenocarcinoma Two MRI findings were frequently observed within the prostate parenchyma in patients with histologically proved adenocarcinoma: (1) a diffuse, relatively inhomogeneous signal intensity throughout the gland, and (2) focal nodules of prolonged T, and T, relaxation times. A diffuse inhomogeneous signal intensity was the most frequent abnormal MRI finding in patients with proved adenocarcinoma, being seen in 31 of the 33 patients (Fig. 5). As mentioned, an indistinguishable inhomogeneous pattern was also observed in 5 of the 12 patients with benign prostatic hypertrophy, rendering parenchymal inhomogeneity a nonspecific finding (assuming no false-negative results on biopsy).

Evaluation of the prostate ?? BRIANT. LARKINETAL.

Fig. 3. (A) Axial spin-echo scan in a patient with benign prostatic hypertrophy (TE 40, TR 500). Prostate is enlarged and has a relatively uniform homogeneous signal intensity. (B) Sagittal inversion recovery scan in another patient with benign prostatic hypertrophy (TI 500, TE 40, TR 2000). Enlarged, homogeneous prostate is clearly differentiated from the surrounding pelvic structures by distinct fascia1 planes. p, prostate, sv, seminal vesicle, b, bladder, r, rectum, s, symphysis pubis, and urrow, retropubic fat.

Fig. 4. Sagittal spin-echo scans in two different patients with benign prostatic hypertrophy. (A) Enlarged, relatively homogeneous prostate (TE 40, TR 500). (B) Markedly enlarged prostate which, unlike that in (A), has a relatively inhomogeneous parenchymal signal intensity (TE 40, TR 500).

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Fig. 5. Axial spin-echo scan in 6%year-old man demonstrates a relatively inhomogeneous parenchyma1 signal intensity (TE 40, TR 500). Rectal exami-

nation had indicated a likely stage C carcinoma. Note the tumor extension into the higher intensity periprostatic fibrovascular tissue on the right (urrows), confirming the clinical impression of extracapsular extension.

The other commonly observed abnormal MRI finding was a focal intraparenchymal nodule of prolonged T, and T2 relaxation times (Fig. 6), being observed in 16 of the 33 patients with adenocarcinoma. This finding appears to be the most specific for intraglandular adenocarcinoma. MRI evidence of neoplastic invasion of the periprostatic fibrovascular connective tissue was demonstrated in 12 of the 33 patients (Figs. $7, and 8). This finding consisted of segmental interruption of the high-intensity periprostatic fibrovascular tissue, usually by relatively inhomogeneous lower-intensity neoplastic tissue, seen on both T,- and T,-weighted images.

Fig. 7. (A) Inversion recovery scan in 55-year-old man with a suspicious prostate on rectal examination demonstrates an inhomogeneous signal intensity, with tumor extension into the periprostatic fibrovascular tissue on the right (right arrow) (TI 500, TE 40, TR 2000). Also note the metastasis in

the left femoral head (lef arrow). (B) Computed tomographic scan at the same level. The superior soft-tissue contrast ability of MRI allows a more accurate delineation of intracapsular and extracapsular neoplasm.

Evidence of seminal vesicle invasion was observed in 7 of the 33 patients (Fig. 9). Findings included gland enlargement, focal areas of prolonged relaxation, and loss of normal fascial planes. MRI was superior to CT in the detection of seminal vesicle involvement. Five of the 33 patients had MRI evidence of adenopathy (Fig. lo), and 5 had MRI evidence of bony metastasis (Fig. 7). MRI and CT were comparable in demonstrating adenopathy and bony metastasis.

Fig. 6. Inversion recovery scan in 66-year-old man demonstrates a well-defined low-intensity (prolonged T2 relaxation) area in the posterior left lobe, consistent with carcinoma (Tl 500, TE 40, TR 2000). Rectal examination indicated a likely benign nodule in the right lobe. Prostatectomy revealed a 4.0 by 2.5 by 2.0 cm grade 2 adenocarcinema in the posterior left lobe.

DISCUSSION Current imaging modalities (CT and ultrasound) have definite shortcomings in the detection and staging of prostatic adenocarcinoma. Our experience with MRI of the prostate is similar to the experience of other authors in that neoplasm confined to the gland can be detected.‘*“” Previous reports indicate that an

Evaluation

of the prostate 0 BRIANT. LARKINETAL.

Fig. 8. A 57-year-old man with likely extracapsular spread of neoplasm on the left on rectal examination. (A) MRI demonstrates an inhomogeneous parenchymal signal texture and tumor invastion of the higher intensity periprostatic fibrovascular tissue on the left (TE 60, TR 2000) (arrows). (B) Computed tomographic scan at the same level.

Fig. 9. Sagittal spin-echo scan shows greatly enlarged seminal vesicle from neoplastic invasion from the prostate (arrows), with loss of the tissue plane between prostate and seminal vesicle (TE 40, TR 500).

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inhomogeneous parenchymal signal intensity may be an accurate finding for adenocarcinoma. In our experience, a relative inhomogeneous signal intensity was observed in nearly all patients with proved adenocarcinoma; however, the same was also observed in 5 of the 12 patients with benign prostatic hypertrophy, rendering it a nonspecific finding. Our most specific finding for adenocarcinoma was a focal nodule of prolonged T, and T2 relaxation times, which was seen in 16 of the 33 patients with adenocarcinoma. This finding was not observed in any patients with benign prostatic hypertrophy or in any normal subjects. The superior soft-tissue contrast of MRI over CT allowed a more accurate delineation of neoplastic extension into the periprostatic fibrovascular tissue and seminal vesicles. The possibility of more accurate staging of prostatic adenocarcinoma eventually may be the most valuable contribution of MRI in the evaluation of the prostate. In our study, the sensitivity of MRI in detecting lymph node and bony metastasis was similar to that of CT. More experience must be accumulated before the role of MRI in the evaluation of the prostate becomes clearly defined. Types of patients in which MRI may have a potential role include (1) those with known prostatic adenocarcinoma in whom MRI may be the superior imaging modality for the accurate delineation of local extension and staging, allowing a more confident selection of the appropriate therapeutic modality, (2) those with a clinically indeterminate prostate nodule because MRI may aid in the decision to pursue a biopsy, (3) those with negative biopsy findings who clinically are suspected of having a neoplasm, and (4) those with occult neoplasms.

Fig. IO. (A) Inversion time scan demonstrates pronounced right-sided pelvic adenopathy in patient with grade 3 adenocarcinoma of the prostate (TI 500, TE 40, TR 2000). (B) Spin-echo scan at the same level (TE 60, TR 2000). Higher signal intensity of the adenopathy on this T,-weighted image makes differentiation of it from surrounding fat difficult.

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