British Journal of Radiology (2007) 80, e15-e18
© 2007 British Institute of Radiology
doi: 10.1259/bjr/23845930
MRI findings of prostatic synovial sarcoma
Y-C Cheng, MD1,
J-H Wang, MD1,
S-H Shen, MD1,
Y-H Chang, MD, PhD2,
P C-H Chen, MD3,
C-C Pan, MD3,
S-C Ko, MD4 and
C-Y Chang, MD1
1 Department of Radiology, 2 Division of Urology Department of Surgery, 3 Department of Pathology, Taipei Veterans General Hospital, 4 Taipei Veterans General Hospital-Healthtech Image Center and National Yang-Ming University School of Medicine, Taipei, Taiwan
Correspondence: Jia-Hwia Wang, Department of Radiology, Veterans General Hospital-Taipei, No. 201, Sec 2, Shih-Pai Road, Taipei 112, Taiwan.. E-mail: wangjh{at}vghtpe.gov.tw
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Introduction
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Synovial sarcoma is a malignant mesenchymal tumour that typically arises in the para-articular soft tissues of the lower extremities in young adults. The tumour is believed to arise not from mature synovial tissue, but from primitive mesenchymal cells that have differentiated to resemble synovial cells under light microscopy. It accounts for 7–10% of all sarcomas. To our knowledge, only four reports of synovial sarcoma involving the prostate have been published [1–4]. However, none of these discussed imaging findings. Accordingly, we now present a case of primary synovial sarcoma of the prostate arising in a relatively young patient who had lower urinary tract symptoms and focus on the imaging findings.
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Case report
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A 45-year-old man presented with weak stream, strain and incomplete voiding, urinary frequency and nocturia 1–2 times per night for about 1 month. Physical examination showed an asymmetric bulging elastic mass over the right lobe of the prostate with a smooth surface. The serum prostate specific antigen (PSA) level was 2.91 ng ml–1. He underwent a MRI examination with a clinical 1.5-T whole-body MR system (Magnetom Sonata; Siemens Medical Solutions, Erlangen, Germany). In order to characterize this prostate mass, we applied the following imaging sequences: (1) gradient-echo T1 weighted (repetition time (TR)/echo time (TE), 241/4.2 ms) axial imaging; (2) spin-echo T2 weighted axial (4320/93 ms) and sagittal (2060/87 ms) imaging; (3) fat-suppressed T1 weighted axial (537/11 ms) and sagittal (597/11 ms) imaging with gadolinium contrast (Omniscan; Amersham, Oslo, Norway) administration with a dose of 0.1 mmol kg–1 (body weight). The imaging study depicted a soft tissue mass measuring about 4 cm x 4.5 cm x 5.0 cm in size, which was well defined and pushed the urethra to the left side. The capsule of the prostate gland was bulging but intact. The tumour revealed isointense signals from the peripheral zone of the prostate on T1 weighted imaging (Figure 1
) and slightly increased signal intensity on T2 weighted imaging with mild heterogeneity (Figure 2). Small cystic spaces within the lesion were also depicted. After intravenous gadolinium administration, slightly heterogeneous enhancement was noted (Figure 3). No obvious regional lymphadenopathy or seminal vesicle and rectum invasion was identified. Biopsy for this prostate mass under transrectal ultrasound guidance was performed and reported as a poorly differentiated malignant tumour. The patient underwent a retropubic radical prostatectomy 2 weeks later. Surgical findings depicted a heterogeneously greyish white tumour located in the right lobe of the prostate (Figure 4). No obvious extracapsular extension or bilateral neurovascular bundles invasion were noted. The diagnosis of primary synovial sarcoma was histopathologically confirmed. Also, cytogenetic evaluation was positive for SYT-SSX type 2 of the t(x;18) translocation. The pathological findings of this case were submitted to Histopathology as correspondence [5]. Seven weeks after surgery, the PSA level fell to 0.00 ng ml–1.
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Figure 1. AxialT1 weighted MR image (TR/TE, 241/4.2 ms) of pelvis demonstrates a mass lesion (arrows) of homogeneous isosignal intensity to the peripheral zone of the prostate, mainly at the right side of the prostate.
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Figure 2. (a) Axial T2 weighted MR image (TR/TE, 4320/93 ms) of the pelvis showing a well-circumscribed mass of heterogeneous increased signal intensity to the peripheral zone of the prostate. The urethra (arrow) is pushed to the left side. (b) Sagittal T2 weighted MR image (TR/TE, 2060/87 ms) of the pelvis shows a cystic component (arrowhead) over the superior posterior portion of the tumour. The tumour is well encapsulated and distinguishable from the surrounding organs, including the urinary bladder (UB) and rectum (arrows).
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Figure 3. Axial fat-suppressed T1 weighted MR image (TR/TE, 537/11 ms) after intravenous gadolinium injection showing mild heterogeneous enhancement of the right prostatic mass (arrows).
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Figure 4. Photograph of a gross specimen demonstrates a heterogeneously greyish white tumour chiefly occupying the right prostate lobe with grossly intact capsule(black arrows).
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Discussion
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Primary prostatic sarcomas are rare tumours which account for less than 0.1% of primary prostate malignancies in adults [6]. The most common histological subtype of prostatic sarcoma is leiomyosarcoma in adults and rhabdomyosarcoma in children [7]. Primary synovial sarcoma occurs in a variety of unusual locations, however, rarely in the genitourinary system; even renal involvement has been reported more often, but is still extremely unusual [3].
Most patients with prostatic sarcoma present with symptoms of bladder outlet obstruction [1, 3, 4, 7]. Our patient complained of weak stream, strain and incomplete voiding, urinary frequency and nocturia 1–2 times per night. The mass effect of the tumour may have been responsible for this symptom.
As compared with the most common malignant tumour of the prostate, adenocarcinoma, prostatic sarcoma occurs in relatively younger patients [7]. According to the previous reports, the age of diagnosis for these patients was 37–63 years [1–4]. The age of our patient (45 years old) was within this range. The PSA level of prostatic adenocarcinoma is often elevated. It was reported that normal serum PSA level was noted in the patients with prostatic sarcoma, which is not surprising given the non-epithelial origin of prostate sarcoma [7]. PSA levels in two previous patients with prostatic synovial sarcoma were 0.5 ng ml–1 and 0.9 ng ml–1 [1, 4]. Our patient had PSA level of 2.91 ng ml–1, which was still within normal range. The PSA level fell to 0.00 ng ml–1 7 weeks after radical prostatectomy. Prostatic sarcoma is often extremely large (7
10 cm) before diagnosis, according to previous reports [7]. Our patient had a slightly smaller tumour (5 cm).
Adenocarcinoma of the prostate typically showed low signal intensity in the hyperintense peripheral zone on T2 weighted MR images and might be enhanced variably after intravenous contrast agent administration [8]. Although the imaging features of synovial sarcoma in prostate was not reported in the literature, in a review of the MRI features of 34 synovial sarcomas of soft tissue in extremities, Jones et al [9] suggested that synovial sarcoma was a relatively large but inhomogeneous lesion which could be clearly differentiated from surrounding tissues. Haemorrhage, fluid–fluid levels and areas of hyperintense, hypointense and isointense signals relative to fat on T2 weighted MR images supported the diagnosis. Both solid and cystic components with haemorrhage and fibrous tissue were responsible for the signal intensity change. Valenzuela et al [10] also evaluated MRI findings of synovial sarcomas in 22 patients, most presenting in the soft tissue of extremities. The most common features were oval and well-defined nodular masses with heterogeneous intermediate signal intensity on T1 weighted images, high signal intensity on T2 weighted images and with heterogeneous contrast enhancement. A cystic component was seen in 77% and intratumoural haemorrhage in 73% of cases. One-third of synovial sarcomas demonstrated calcification of the tumour [11]. In contrast, in the less typical regions, such as chest, synovial sarcoma revealed an image of well-defined margin with heterogeneous contrast enhancement and no calcification [12]. Over head and neck regions, most synovial sarcomas were homogeneous with smooth margins and presented isointense on T1 weighted images and isointense or hypointense on T2 weighted images. Only one case (1/8) showed calcification [13]. No cystic part was mentioned. In our case, the synovial sarcoma behaved as a well-demarcated lesion with isointensity to the peripheral zone of the prostate on T1 weighted images; slightly increased signal intensity on T2 weighted images and slightly heterogeneous enhancement and cystic component. No obvious haemorrhage or fluid–fluid level appearance were observed.
Due to the rarity of synovial sarcoma involving the prostate, definitive treatment protocol have not been clearly established. It appears that aggressive resection should be the rule. However, the prognosis is poor for patients with prostate sarcoma treated with surgery alone [6]. The role of chemotherapy and/or radiation therapy for prostatic synovial sarcoma remains unknown.
In conclusion, although the imaging findings of primary synovial sarcoma of the prostate are not unique and pathological study is the only way to make a definite diagnosis, the MRI features of prostatic synovial sarcoma are different from the characteristic findings of prostatic adenocarcinoma. If a relatively young man presents with a large and well-demarcated tumour in the prostate and a normal PSA level, synovial sarcoma may be included in the differential diagnosis, especially when the imaging features show increased signal intensity on T2 weighted image and mild heterogeneous contrast enhancement on MRI.
Received for publication September 8, 2005.
Revision received January 25, 2006.
Accepted for publication February 7, 2006.
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References
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Introduction
Case report
