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TITLE: Scrotal PNET in an Adult Patient: Radiologic-Pathologic Correlation.

AUTHORS:

Mª Gabriela Tirapu-de-Sagrario, Sandra Baleato-González, Elena Pintos-Martínez and Roberto García-Figueiras

KEY WORDS:

Neuroectodermal Tumors, Scrotum, Sarcoma, Groin, Inguinal Canal

INTRODUCTION

We report a, histologically confirmed, rare case of a peripheral primitive neuroectodermal tumor (pPNET) originating from the scrotal sac in an adult patient. This report emphasizes the important role of pathology examination to reach final diagnosis on the basis of immunohistochemistry and electronic microscopy findings. Outcome depends upon the localization and staging of the tumour, age of the patient, histologic classification, extent of surgical resection and time to treatment.

CASE REPORT

An 84-year-old man was admitted to our hospital with an inguinoscrotal, irreducible, painless mass with a hard consistency, which had progressed over the last six months. There was no presence of urinary or intestinal symptoms. Alpha-Fetoprotein, beta-HCG and LDH values were found to be normal. The patient was subsequently referred to the Urology Departament and he underwent a pelvic MRI. It confirmed a 12x11x19 cm solid mass, which demonstrated central areas of necrosis and subtle amounts of haemorrhage (Figure 1). This mass demonstrated marked and heterogeneous enhancement after intravenous gadolinium administration as well as evidence of internal vascular flow. Both testes showed a normal morphology and signal on T2-weighted sequences (Figure 1). Surgical excision was performed by the Urology Service and they reported that the spermatic cord, femoral vessels and testes were displaced but not infiltrated by the mass (Figure 2A). Despite the fact that a sarcoma was the suggested diagnosis on imaging, this case exhibited microscopic pathology features of a rare pPNET tumor in an unexpected location. The presence of neurosecretory granules in the electron microscopy (Figure 3) and the EWS-FLI1 traslocation confirmed the diagnosis.

DISCUSSION

pPNET is an uncommon tumor that belongs to the Ewing’s Sarcoma family of tumors (1-4). It is an aggressive neoplasm, with large size at presentation, which metastasizes rapidly and predominantly affects children and adolescents (1,3,5).The most common locations are: the chest wall, paraspinal area in the chest, abdomen and pelvis (7,8). Ellinger J, et al (1), performed a MEDLINE search identifying renal, bladder, prostate, ureter and seminal cord PNETs, Hari S et al (3) and Kim MS et al (9) also described kidney and retroperitoneum cases and even an uterus case was described by Peres E et al (10) but, to our knowledge, this is the first pPNET case which originated in the scrotal sac, independent of any organ. This tumor is extremely rare in adults and the clinical findings (large painful mass) do not help to distinguish a benign from a malignant tumor (11). At the presentation most of them grow as scrotal masses rather than inguinal masses because they usually originate just below the external inguinal ring (12).

PNET tumor shows no specific imaging features, but radiological studies are useful to rule out other possible etiologies, to define the location of the tumor and its morphological characteristics as well as its distance extension (1,3,4). In order to diagnose PNET, and differentiate it from other tumors of the Ewing family, we need to demonstrate the expression of some neural markers on the inmunohistochemical stains, including neurofilament, NSE, Leu-7, vimentin, S-100, CD-56, chromogranin and synaptophysin (2). A definitive finding is the EWS-FLI1 traslocation and the presence of neurosecretory granules in electron microscopy (7,8).

In conclusion, we present a histologically confirmed case of an extratesticular peripheral scrotal PNET, which possibly originated from a remnant of neuroectodermic cells of the neural crest. In a case like this one, with a huge genital mass, ultrasound and MRI are very useful modalities to assess the location of the mass, its dependency on any other organ and the tumoral internal structure. These will help us to suggest a possible differential diagnosis however the definitive diagnosis requires histopathological and immunohistochemical examination.

REFERENCES

1. Ellinger J, Bastian PJ, Hauser S, et al. Primitive Neuroectodermal Tumor: Rare, highly aggressive differential diagnosis in Urologic Malignancies. J Urol 2006; 68(2):257-262
2. Gurung P,Attar K andPeters J. Primitive neuroectodermal tumorof thespermatic cord. Int J Urol.2010 Jul;17(7):679-80.
3. Hari S,Jain TP,Thulkar S, et al. Imagingfeaturesofperipheral primitive neuroectodermal tumours. Br J Radiol.2008 Dec;81(972):975-83.
4. Javery O,Krajewski K,O’Regan K,el al. A to Z of extraskeletal Ewing sarcoma family of tumors in adults: imaging features of primary disease, metastatic patterns, and treatment responses. AJR Am J Roentgenol.2011 Dec;197(6):W1015-22.
5. Ibarburen C, Haberman JJ, Zerhouni EA. Peripheral primitive neuroectodermal tumors. CT and MRI Assessment. Eur J Radiol. 1996 Feb;21(3):225-32.
6. Fontaine C,Schots R,Braeckman J, et al. Long-term survival in an adult metastatic renal peripheral primitive neuroectodermal tumor (PPNET) with multimodality treatment including high-dose chemotherapy. Ann Oncol.1997 Jul;8(7):691-4.
7. Khong P.L, Chan G.C.F, Shek T.W.H, et al. Imaging of Peripheral PNET: Common and uncommon locations. Clinical Radiology. 2002;57:272-277
8. Hoffer FA, Gianturco LE, Fletcher JA, et al. Percutaneous Biopsy of Peripheral Primitive Neuroectodermal Tumors and Ewing’s Sarcomas for Cytogenetic Analysis. AJR. 1994;162:1141-1142
9. Kim MS, Kim B, Park CS, et al. Radiologic Findings of Peripheral Primitive Neuroectodermal Tumor Arising in the Retroperitoneum. AJR. 2006; 186:1125-1132.
10. Peres E, Mattoo TK, Poulik J, et al. Primitive Neuroectodermal Tumor (PNET) of the Uterus in a Renal Allograft Patient: A Case Report. Pediatr Blood Cancer. 2005;44:283-285.
11. Lioe TF and Biggart JD. Tumours of the Spermatic Cord and Paratesticular Tissue. A Clinicopathological Study. British Journal of Urology. 1993; 71:600-606
12. Rodríguez D and Olumi AF. Management of spermatic cord tumors: a rare urologic malignancy. Ther Av Urol. 2012: 4(6): 325-334

FIGURE LEGENDS

Figure 1

A) Axial T2 TSE shows a large heterogenous inguinoscrotal mass that displaces the penis (void arrows) but apparently not infiltrates it. B) Axial T1 after intravenous contrast – Maximum relative enhancement. It shows central hypoperfusion (black arrows), which is hyperintense on T2 sequences, probably due to necrosis or hemorrhage, and a solid hypervascularized periphery (white arrows).

Figure 2

A) Surgical photograph shows the spermatic cord (white arrows), which is displaced but not affected by the large mass. B) A long axis section of the mass. It’s observed an heterogenous tumor of mottled appearance with partially embossed, clear brownish areas, which are the solid ones (black asterisks). It also has extensive necrotic and hemorrhagic component (white asterisks).

Figure 3

Electronic Microscopy. The presence of neuroendocrine granules (white circles) of various sizes (from 80 to 120 nm) in the cytoplasm of the tumor cells is confirmed. This finding demonstrates the neuroendocrine differentiation of the neuroectodermal tumor.