Teaching Case

A 16-year-old girl presents with nonspecific and insidious abdominal symptoms such as discomfort, abdominal pain, and distention. The patient came to the emergency room due to pain in the right hemiabdomen. An ultrasound (US) and Computed Tomography (CT) were performed, depicting a central abdominal mass. She was subsequently referred to our hospital for further evaluation. All tumour markers were negative. Lactate dehydrogenase was elevated (621 UI/L, NV 120–246) without any lysis syndrome biochemical alterations.

The US showed a large, hypoechogenic, well-defined, heterogeneous mass in the centre of the upper abdomen. No evident Doppler signal was observed within the tumour, but prominent vascular structures were seen around it. It also depicted splenomegaly (Figures 1a, 1b and 1c).

The initial contrast-enhanced CT revealed a large intraabdominal polylobulated mass with central hypodense areas of necrosis/cystic degeneration, peripheral solid-enhancing areas, and the presence of aberrant vascularity (Figures 2a, 2b, 2c and 2d). Multiple metastatic implants were found in the peritoneum, mesentery (Figures 2e and 2f), and liver (Figure 2a).

MRI demonstrated a heterogeneous mass, predominantly hypointense in T1W (not shown), and hyperintense in T2W, with marked diffusion restriction, low ADC values, and evident heterogeneous contrast enhancement (Figures 3a, 3b, 3c and 3d).

Due to the patient’s anaemia and abdominal pain, an urgent digital subtraction angiography (DSA) was performed (Figures 4a and 4b), which showed no bleeding.

Also, a staging PET-CT (Figures 6a and 6b) was performed, and it showed high FDG uptake in both the tumour and the metastasis. The tumour biopsy (Figure 5) stated the diagnosis.

After two years of various chemotherapy treatments, follow-up CT showed slight tumour growth; however, the necrotic/cystic centre had become more pronounced. Additionally, several new metastatic implants were observed in the mesentery, liver, and retroperitoneal lymph nodes (Figures 7a and 7b).

Background

Perivascular epithelioid cell tumour (PEC) is a rare mesenchymal neoplasm that includes lymphangioleiomyomatosis, angiomyolipoma, clear cell “sugar” tumour, and other mesenchymal tumours that can arise from any location; Mesenteric PECs are extremely rare, and only a few cases have been described [1–3]. Usually, these tumours can exhibit distinct perivascular epithelioid and spindle cell morphology that express melanocytic and myogenic markers [2–4], and HMB45 is considered the most sensitive melanocytic marker in PEComas [2].

The TFE3 gene is located on Xp11.2, and its translocation often leads to upregulation of TFE3 and subsequent cell proliferation and oncogenesis.

Clinical Perspective

The aetiology of PECs remains unclear [2]. Patients are usually asymptomatic, and eventually, a mass might be detected accidentally during a physical examination or through imaging tests [4]. When symptoms do occur, they are usually nonspecific and include abdominal discomfort, nausea, weight loss, or abdominal pain. Symptoms often relate to the organ or location of the PECs, frequently resulting from a compressive effect [2].

Imaging Perspective

It is important to note that the imaging findings are non-specific. Due to the rarity of these tumours, anatomopathological diagnosis is almost always required [1–5].

In scans, PECs appear as well-defined, hypodense, polylobulated masses of variable size. In non-contrast CT scans, they are usually homogeneous masses. In non-contrast MRI, they tend to be hypointense in T1W and heterogeneously hyperintense in T2W compared to skeletal muscle. Solid areas usually show diffusion restriction. Some types of PECs, such as angiomyolipoma, contain fat [2,5].

PECs usually show heterogeneous arterial and venous enhancement with or without areas of necrosis or cystic degeneration [2,4,5]. Homogeneous enhancement is also described [5].

Calcifications are uncommon with few references to renal PECs [5].

The most frequent sites of metastasis are the lung, liver, and retroperitoneum [5].

Outcome

All gastrointestinal PECs have malignant potential, and close follow-up with imaging is required [2,4].

Due to their rarity, there is no well-established optimal treatment currently. Surgical resection, aiming for complete removal, is the initial choice. Chemotherapy and immunotherapy are treatment options, especially in initially non-resectable cases [2–4].

PEComas are known to harbour TSC2 mutations. A minority of PEComas contain TFE3 gene rearrangements. Also, TFE3 immunoreactivity has been described in younger patients, predominantly women [3], as observed in our case.

Our patient is currently in a Temozolomide and CDK4/6 inhibitors clinical trial.

Teaching Points

• PECs are usually benign, but malignancy or malignant behaviour is common.
• Close follow-up with imaging is essential.
• TFE3-expressing or mutated mesenteric PEComa is rare and more frequent in young women.
• Imaging findings are nonspecific, and a biopsy is almost always necessary.

All patient data have been completely anonymised throughout the entire manuscript and related files.