A quite rare prostatic tumour

Clinical History

A 28-year-old Caucasian man complaining of right testicular pain for the past 4 months, associated with progressive tenesmus and anal pain, presented for medical evaluation.
Digital rectal examination revealed a firm, painful, lobulated mass along the anterior wall of the anorectum.
The patient’s serum prostate-specific antigen level was 0.48 ng/mL.

Imaging Findings

A pelvic Magnetic Resonance (MR) was performed, revealing a 62 x 60 x 70 mm solid heterogeneous mass, with irregular borders replacing the prostate gland, involving both the levator ani muscles and extending to the posterior and left peri-rectal fat, with close contact with the internal obturator muscle (without clear invasion) and possible adherence to the anterior anorectal wall. The urethra was deviated to the right but the tumour did not invade other organs.
This lesion was isointense to muscle on T1, with intermediate signal on T2 and peripheral contrast enhancement with central necrotic areas. It revealed restricted diffusion with low signal on the ADC map favouring an elevated cellularity lesion.
Additionally, there were enlarged necrotic lymph nodes in the pelvis: one pre-sacral adherent and invading the left rectal wall; one obturator and the other at the left iliac bifurcation.
A prostate biopsy revealed sheets of uniform small round blue cells.

Discussion

Primary prostate sarcoma results from the mesenchymal components of the prostate stroma and accounts for less than 0.1% of primary prostate tumours [1].
Ewing’s sarcoma (ES) and peripheral neuroectodermal tumour (PNET) are “small round blue cell tumours”, presenting in adolescents and young adults aged 10-20 years, with a slight male preponderance [2].
PNET/ES are reported to occur in various organs, however, to our knowledge there are fewer than 10 cases described in the prostate [3-5].
The majority of cases share the cytogenetic translocation t(11;22) (q24;q12), with occasional variations, and the term, “PNET/ES” is currently favoured for this tumour family [6, 7].
From the literature case description these patients frequently present with symptoms of dysuria or pelvic discomfort, as the present case. The mass effect of the tumour over the urethra or the rectal wall probably causes the symptoms [4].
The PSA levels are relatively low in comparison with prostatic adenocarcinoma [1, 4, 5].
These tumours are frequently large at diagnosis, some presenting with lymph node and/or lung metastasis [2, 4-6].
The few case reports in the literature describing the MR findings of PNET/ES emphasize heterogeneously enhancing large multinodular masses centred on the prostate, with internal non-enhancing areas of necrosis and/or haemorrhage, as presented in this case. As in other prostate sarcomas our case of PNET/ES showed marked high signal intensity at DWI with very low ADC values. The imaging features shown reflect the high cellularity and aggressiveness of this tumour [4, 5, 8].
PNET/ES does not resemble prostatic adenocarcinoma on MR, and this technique may play a role differentiating these two types of tumour. MR is also helpful in localizing and delineating the extent of the disease, nevertheless, final diagnosis of PNET/ES requires immunohistochemical study: the positive expression of CD99, a cell-surface glycoprotein involved in cell adhesion, plays a crucial role in distinguishing PNET/ES from other rare entities such as lymphoma, rhabdomyosarcoma and other neuroendocrine cancers [7].
Data on long-term follow-up are limited, but it seems that radical surgery and chemotherapy may be needed to treat Ewing’s sarcoma/PNET. Some patients have also been submitted to external radiotherapy. However, the prognosis is very poor, with most patients being disease-free no more than 24 months after treatment [4].

Differential Diagnosis List

Final Diagnosis

Prostate gland primary Ewing's sarcoma/peripheral neuroectodermal tumour

URL:	https://www.eurorad.org/case/11600
DOI:	10.1594/EURORAD/CASE.11600
ISSN:	1563-4086