Solitary lesion of the canal of Nuck

A 26-year-old woman presented to our institution with a 3-year history of a slow-growing, painless, mobile vulvar nodule. Physical examination revealed a painless, soft, and mobile nodule in the left groin, extending to the left labia majora, with no inflammatory signs. Ultrasound was requested for further characterization, followed by magnetic resonance (MR).

Ultrasound revealed a solid, homogeneous, and hypoechogenic mass in the subcutaneous tissue of the left labia majora, with a slightly lobulated contour. The lesion presented with hypervascularity on colour Doppler imaging (Fig. 1).

A complementary MR was performed, showing a well-circumscribed subcutaneous lesion in the left labia majora, slightly heterogeneous, with intermediate-to-high T2-weighted signal intensity and low signal intensity on both T1-weighted and T1-fat-suppressed sequences (Fig. 2). On diffusion-weighted sequences, the lesion did not show restriction.

Post-contrast images revealed strong and homogeneous enhancement in the arterial phase, confirming the hypervascular nature of the tumour, which persists during the venous and delayed acquisitions, despite being less expressive (Fig. 3).

The patient was referred for surgical excision. Histopathologic examination confirmed the diagnosis of a solitary fibrous tumour of the canal of Nuck.

The canal of Nuck is the female equivalent of the processus vaginalis in males and is defined as a small evagination of the parietal peritoneum [1]. Typical clinical presentation of the canal of Nuck pathology includes a mass or painless/painful swelling in the groin or labial area.

Solitary fibrous tumours (SFT) are rare slow-growing mesenchymal neoplasms of fibroblastic or myofibroblastic origin, accounting for less than 2% of all soft-tissue tumours [2]. Although more commonly found in the pleura, SFT can virtually arise anywhere in the body [3].  They usually arise in the 5^th and 6^th decades, with equal gender distribution [3]. Clinical presentation includes local pain and palpable mass. Symptoms due to local mass compression are also described, namely neuropathic pain [2]. Nevertheless, SFT may also be asymptomatic.

Pelvic SFTs are rare and generally arise from the pelvic peritoneum, which can explain the pathophysiology of the lesion from our case report [2]. Vulvar SFT is even rarer, and only 25 cases have been reported in the literature [4].

Imaging features can vary widely according to the cellularity, vascularity, and density of the lesion’s stroma [2]. On ultrasound, SFTs classically present as hypoechoic masses. Additional imaging features will directly depend on the lesion specificities [5].

On computed tomography (CT), these tumours typically present as well-circumscribed, hypervascular lesions, sometimes with central non-enhancing areas, related to necrosis or cystic degeneration. Calcifications are rare [2].

At MR imaging, SFT features intermediate signal intensity on T1-weighted images and variable signal intensity on T2-weighted images. T2 signal will correlate with the cellularity, collagen content and lesion degeneration [5]. Hypercellular lesions usually present with intense arterial enhancement that persists in the venous and delayed phases. On the other hand, areas of necrosis and cystic degeneration won’t enhance after paramagnetic contrast administration.

Currently, surgery is the treatment of choice of SFT. The role of radiotherapy and chemotherapy in SFT management is still limited and remains uncertain [3]. Routine follow-up is advised after surgical resection, given the possibility of local recurrence [2].

One year following surgery, the patient maintains periodic surveillance and remains asymptomatic.