Peripheral primitive neuroectodermal tumour (PNET) of the vulva

Clinical History

A 36-year-old woman with no significant past medical history presented with a painless vulvar mass. At physical examination, a mass of elastic consistency and a smooth surface was found in the vulva, between urethra and vagina.

Imaging Findings

US examination revealed a solid and vascularized mass with oval morphology and well-defined margins.
MR pelvic images evinced a mass measuring 2.4 x 3 x 2.7 cm, located in the vulva. A precise tumour origin was difficult to locate due to its position between the lower third of the urethra and the anterior wall of the vagina. For this reason endovaginal contrast was used. The mass was isointense on T1W images, hyperintense on T2W images, and demonstrated low ADC values. Dynamic contrast-enhanced images showed a mass with homogeneous and early enhancement, a peripheral ring, and a curve type II (enhancement kinetics). Neither peritoneal lesions nor pelvis lymphadenopathy was detected.

Discussion

Histology following tumour excision reported a primitive neuroectodermal tumour (PNET) of the vulva. 18F-FDG PET/TC was performed with no evidence of distant disease.

PNETs represent a group of aggressive tumours with low incidence and are composed of small and round cells with neuroectodermal origin. These tumours can be subdivided into: PNET from the central nervous system and peripheral PNET (pPNET). pPNET may originate in the peripheral nerves or soft tissues, and it has been considered a member of Ewing’s sarcoma family of tumours because of its similar chromosomal translocations [1].

The most commonly reported locations include the paravertebral region, lower extremities, and chest wall, among others [2]. The feminine genital tract is a very uncommon origin and only a small number of reports have described vulvar lesions [3-8].
pPNETs affect particularly the first three decades of life, with no gender differences. Clinical presentation is variable depending on the location of the tumour. Pain or tenderness are common although most of the cases reported in the vulva were painless lesions [2].

pPNETs show nonspecific imaging features. At ultrasonography they are most frequently hypoechoic with an increased blood flow. Anechoic areas depicting necrosis or haemorrhage may also be present.
MR, CT, and PET/CT play complementary roles in assessing the local tumour resectability and the presence of metastatic disease, as well as evaluating response to treatment [2, 9].
However, MR is the modality of choice to characterize tumours in the perineum and pinpointing its location and relations with neighbouring structures, because of its better spatial resolution [10]. It can also provide additional useful information such as the tumour malignancy grade through the diffusion images or contrast enhancement pattern. MRI findings are variable since either a mass with well-defined margins or an infiltrative growth have been described. Calcification, haemorrhage and necrosis may also be present, and a prominent contrast enhancement is usually seen in both CT and MR [2]. Nevertheless, tumours smaller than 3 cm as in our case may not show the above features.

Treatment is usually a combination of surgical resection and chemotherapy that may be supplemented with radiotherapy. Although numerous factors have been associated with a bad prognosis: the tumour size, the type of cytogenetic aberration, the metastatic disease at presentation, an early recurrence …[2], a relatively favourable outcome has been observed for pPNET arising in superficial sites, probably related to a smaller size, superficial location, or complete surgical removal of the cases [11].

Differential Diagnosis List

Final Diagnosis

Peripheral primitive neuroectodermal tumour (PNET) of the vulva

URL:	https://www.eurorad.org/case/14045
DOI:	10.1594/EURORAD/CASE.14045
ISSN:	1563-4086