PMC4573405_01
A Large prepatellar mass following incisional biopsy. B. Excised gross specimen: gray/brown multinodular, encapsulated, and hemorrhagic mass measuring 55 x43 x 27 mm with negative gross margins. C. Surgical defect following excision. Ruler demonstrates cm increments. D. Final aspect of the wound 2.5 years post-operative.
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On physical exam, there was limited range of motion at the left knee joint; a heterogeneous mass (60 mm x 50 mm x 50 mm) appeared on the anteroinferior aspect of the left knee, which was exquisitely tender with surrounding erythema and warmth (Fig. 1a,b). The mass also demonstrated small areas of ulceration (Fig. 1a). Grossly the specimen demonstrated a gray/brown multinodular, encapsulated, and hemorrhagic mass measuring 55 mm x 43 mm x 27 mm with negative gross margins (Fig. 1).
T1-weighted MR images of a large soft tissue mass of the left subpatellar area (A) in the sagittal plane (TE: 18 ms, TR: 688 ms) and (B) in the coronal plane (TE: 11 ms, TR: 552 ms), measuring 64 mm craniocaudal x 59 mm transverse x 41 mm anterior-posterior mass. This soft tissue mass is lobulated and of low to intermediate strength on T1-weighted images. The lesion does not appear to invade the patellar tendon, bone or joint space.
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MR imaging (Siemens Symphony 1.5T) demonstrated a heterogeneous 64 mm x 59 mm x 41 mm mass, centered in the prepatellar subcutaneous fat, abutting the patellar tendon (Fig. 2). There was intermediate signal strength on T1 (Fig. 2), heterogeneous signal strength on T2 (Fig. 3), and marked signal enhancement with gadolinium (Fig. 4).
T2-weighted MR image with intravenous gadolinium infusion demonstrates marked heterogeneous enhancement of the lesion (TE: 86 ms TR: 4240 ms). This finding in addition to the serpiginous vascular malformations surrounding the lesion is highly suggestive of a glomangioma. The enhancement contrasts with that seen in sarcomas where the outer margins of the lesions enhance to a greater degree.
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There was intermediate signal strength on T1 (Fig. 2), heterogeneous signal strength on T2 (Fig. 3), and marked signal enhancement with gadolinium (Fig. 4).
A. Large dilated vessels with surrounding hemorrhage, normal endothelial cells and glomus cells. B. Large vessels with infiltrating glomus cells. C. Small rounded cells with eosinophilic cytoplasm encircling vessels indicates glomus cells. D. Smooth muscle actin confirmed by immunohistochemistry indicates glomus cells.
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Histopathology demonstrated a monomorphic population of small, round, eosinophilic cells with minimal atypia (Fig. 5). Immunohistochemistry was positive for smooth muscle actin (Fig. 5) and negative for cytokeratin, S-100, and CK-34.