HMB-45 negative angiomyolipoma of the orbit: a case report and review of the literature

An 80-year-old woman had a 2-year history of progressive fullness in the left upper eyelid. External examination revealed 3 mm of relative proptosis of the left eye and a nontender palpable firm mass in the left superonasal orbit (Fig. 1a). The remainder of the ocular examination was within normal limit. Past medical history was otherwise unremarkable. Computed tomographic scan demonstrated a circumscribed, heterogeneous orbital mass displacing the left globe laterally (Fig. 1b, c and d). Surgical removal of the tumor was performed through anterior orbitotomy in an en bloc fashion. At the time of surgery, the 1.8 × 1.8 × 1.3 cm yellowish mass was encapsulated and solid (Fig. 2a). Histologically, the orbital mass was composed of mature adipocytes, intermingled with spindle or oval-shaped cells with eosinophilic cytoplasm, accompanied by thick-walled blood vessels (Fig. 2b). Immunohistochemically, tumor cells were positive for CD34 and HHF-35 (Fig. 2c and d), but negative for cytokeratin, HMB-45 and Melan-A. These findings confirmed the diagnosis of angiomyolipoma. Systemic check-up was unremarkable. No recurrence was noted at 2-year follow-up.

Primary orbital angiomyolipoma is a rare entity of orbital tumor. Until now, only 4 cases of ocular perivascular epithelioid cell tumor (PEComa) have been reported, and all had positive melanocytic markers [2‐4]. All reported 4 cases of ocular PEComas were female and their tumor location was eyelid (2 cases), ciliary body (1 case), and orbit (1 case) respectively. PEComas often share overlapping histopathological features with epithelioid cells along a perivascular distribution and characteristic immunohistochemistry with coexpression of myoid and melanocytic markers (HMB-45 /or Melan-A) [5]. Current case is unique in that the tumor lacked reactivity for melanin-associated antigens HMB-45 and Melan-A, which is similar to some angiomyolipomas from skin, head and neck [6‐9]. The HMB-45 negativity may be explained by the rarity of the epithelioid cells in these cases, and the HMB-45 positivity is often weaker or absent in spindle cells [9]. In addition, these angiomyolipomas are usually relative small, contrary to what happens to kidney and liver tumors, which are often large. However, because of the small number of reported cases, whether these HMB-negative angiomyolipoma is a new variant of PEComas require further investigation. Differential diagnosis should include giant cell angiofibroma which is a highly vascular tumor comprising a spindle-cell proliferation with numerous multinucleated giant cells and pseudovascular spaces, and immunohistochemically positive for CD34, CD99, and vimentin [10].

Approximately one third of renal angiomyolipomas occur in patients with tuberous sclerosis. However, this association has been rarely reported in extrarenal angiomyolipoma, including of ocular angiomyolipoma. Because most angiomyolipomas contain varied amounts of adipose tissue, image features of fat attenuation at unenhanced CT may help in diagnosis. Although most angiomyolipomas show a benign course, some reports have suggested that histologically atypical angiomyolipomas are potentially malignancy. Therefore, wide excision and regular follow-up are warranted.