Renal epithelioid angiomyolipoma in a patient with tuberous sclerosis
His haemodynamic parameters were within normal limits. There was a clinically palpable mass in the left iliac fossa. An abdominal computed tomography (CT) scan showed a massive left retroperitoneal haematoma arising from a 15.0 × 16.2 × 16.3‐cm heterogeneous mass in the lower pole of the left kidney (Fig. 1), likely a renal cell carcinoma (RCC) or angiomyolipoma (AML).
The patient underwent left open radical nephrectomy, performed through a midline incision. A left‐sided mass greater than 20 cm in width was excised along with the left adrenal gland (Fig. 2). No signs of intra‐abdominal metastasis were noted. Histopathology showed features consistent with epithelioid angiomyolipoma (EAML) (Fig. 3).
The patient had an uneventful recovery in the intensive care unit. He had ongoing clinical surveillance but presented 3 years later with worsening dyspnoea secondary to lung metastases, presumed to be EAML.
Renal AML is a typically benign neoplasm consisting of adipose tissue, smooth muscle and thick walled blood vessels in varying proportions.1 Diagnosis is usually incidental on a CT abdomen, although patients may present with vague abdominal pain, a palpable mass, macroscopic haematuria, retroperitoneal haemorrhage, shock or even death. Surgical treatment is advocated for symptomatic patients, or if the tumour is greater than 4 cm in size, or if there is suspicion of malignancy.2
It is difficult to differentiate AML with minimal fat from RCC. Characteristics peculiar to AML with minimal fat include homogeneous enhancement, prolonged enhancement pattern, high tumour attenuation on unenhanced scans and less mean enhancement.3 AML can occur as an isolated renal lesion, or as a part of a hereditary process most commonly related to TSC in up to 50% of cases. However, as many as 90% could be sporadic having no association with TSC. They can occur as small lesions, bilateral or multi‐focal.4 CT‐guided biopsy of the lesion can improve diagnostic accuracy, particularly for small tumours of less than 4 cm in size.5
EAML, a member of a family of mesenchymal tumours known as perivascular epithelioid tumours, is a rare variant of AML, seen in 8% of renal AMLs with pure EAML accounting for less than 1% of total cases.6 EAML is characterized by the presence of polygonal epithelioid cells with densely eosinophilic cytoplasm and varying degrees of nuclear atypia.7 Malignant behaviour has been observed in EAML, which is in stark contrast to the benign biological behaviour of classic AML. In up to 30% of patients, extension into perirenal tissue or inferior vena cava, local recurrence, or nodal, hepatic, pulmonary or spinal metastases can occur,4 also demonstrated by this case report.
The prevalence of EAML may be more than what is reported in the literature as it may be misdiagnosed as RCC. In the study carried out by Eble et al.,7 four out of five cases of EAML were initially diagnosed as carcinoma based upon radiological and histological appearances. Pea et al. studied five tumours and concluded that three had features consistent with EAML.9 Differentials for EAML are RCC, oncocytoma, medullary carcinomas and sarcomatoid RCC. The absence of delicate vascular network and alveolar and tubular architectural pattern differentiates EAML from RCC. Immunohistochemistry markers help facilitate the diagnosis. HMB‐45 antigen, a melanosome‐associated protein, has shown immunoreactivity and has been demonstrated in renal AML. The fact that AML is uniformly positive for melanoma (HMB‐45, melan‐A) and smooth muscle markers (HHF‐35, SMA and Caldesmon) has provided a definitive marker for the diagnosis.