Angiomyomatous hamartoma (AMH) of the lymph node is characterized by partial replacement of normal nodal parenchyma by disorganized blood vessels and smooth muscle cells with or without adipose tissue within a fibrous stroma. Inguinal and femoral lymph nodes are commonly involved, 1-3 while popliteal lymph node involvement is uncommon. 4,5 We report a rare case of AMH of the popliteal lymph node in a young patient with a clinical diagnosis of Baker’s cyst. An 18-year-old male presented with pain and swelling in the left popliteal fossa lasting 3 years. The swelling slowly increased in size. There was no history of any trauma, fever, tuberculosis, weight loss, or chronic illness. A clinical diagnosis of Baker’s cyst was made without any imaging studies. The lesion was operated on under local anesthesia. The swelling persisted, however, and physical examination revealed a 1.5 cm-sized, mildly tender, non-reducible, firm mass in the left popliteal fossa. An magnetic resonance imaging (MRI) scan revealed a 1.5 ×1.0-cm soft tissue mass close to the popliteal blood vessels without encasing them (Fig. 1A, B). No cyst was seen. The radiological differential diagnoses offered were benign neoplasm and pseudotumor. The left popliteal fossa was explored again and a firm, soft tissue mass loosely adherent to the popliteal blood vessels was identified and excised. The postoperative period was uneventful. Hematoxylin and eosin–stained sections revealed a lymph node with partial replacement of the parenchyma from the hilum to the cortex by fibrous tissue containing several ir regular blood vessels of varying sizes, interspersed with spindle cells and smooth muscle cells (Fig. 2A, B). Mature adipose tissue infiltration was seen in a small area near the hilum of the lymph node (Fig. 2C). The capsule was thickened. The subcapsular and medullary sinuses were obliterated. Cortical lymphoid tissue showed variable atrophy. Immunohistochemistry with a primary antibody against smooth muscle actin (SMA; 1:400, Thermo Scientific, Waltham, MA, USA) demonstrated smooth muscle cells in the blood vessel walls and in the stromal tissue (Fig. 2D, E). The rich vascularity of the lesion was highlighted by CD34 antibodies (1:100, Diagnostic BioSystems, Pleasanton, CA, USA) (Fig. 2F). A diagnosis of AMH of the lymph node was made.
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