Fibroma-like perivascular epithelioid cell tumor: a rare case in a long bone
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CASE REPORT
Fibroma-like perivascular epithelioid cell tumor: a rare case in a long bone Sara Ramezanpour 1 & Andrew E. Horvai 2 & Melissa Zimel 3 & Matthew Bucknor 1 & Thomas M. Link 1 Received: 21 July 2020 / Revised: 2 September 2020 / Accepted: 10 September 2020 # ISS 2020
Abstract Fibroma-like perivascular epithelioid cell (PEComa) tumor is an extremely rare family of mesenchymal tumors composed of cells co-expressing melanocytic and myogenic markers. To date, 13 cases of primary bone PEComa have been reported in the literature and five reported fibroma-like PEComas were found in the soft tissues of patients with tuberous sclerosis (TSC). However, no fibroma-like PEComa has been reported in bone, either sporadic or TSC-associated. Here we report the case of a 22-year-old man with known TSC, who presented for evaluation of an asymptomatic mass in his left fibula diaphysis that had been present for 5 years. He had no activity-related pain, numbness, weakness, or limitations in range of motion. Both 3-T MRI and CT demonstrated a tumor originating from the midshaft middiaphyseal fibula. Axial T1-weighted and fat-saturated T2weighted fast spin echo images showed a well-defined lesion in the fibula with extension into the surrounding soft tissues. Whole body bone scan was negative for metastasis using technetium-99m. Renal ultrasound was unremarkable with no evidence of angiomyolipoma. Histopathology demonstrated isolated spindle cells in a dense collagenous matrix. By immunohistochemical staining, tumor cells were positive for HMB-45 and MiTF and partially positive for alpha-smooth muscle actin supporting a diagnosis of fibroma-like PEComa of the midshaft fibula. Although fibroma-like PEComa of bone is very rare, a bone tumor in the setting of TSC should raise suspicion for the diagnosis, in particular if histology demonstrates rare epithelioid cells in a densely fibrotic stroma. Keywords Fibroma-like PEComa . Bone tumor . Tuberous sclerosis
Introduction Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal neoplasm with neoplastic cells demonstrating both * Sara Ramezanpour [email protected] * Thomas M. Link [email protected] Andrew E. Horvai [email protected] 1
Department of Radiology and Biomedical Imaging, University of California, San Francisco, 400 Parnassus Ave, A-367, San Francisco, CA 94143, USA
2
Department of Pathology, University of California, San Francisco, San Francisco, CA, USA
3
Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA, USA
melanocytic and smooth muscle differentiation [1]. PEComas most commonly involve the kidney as angiomyolipomas but can be found in other organs such as the intestinal tract, gynecologic tract, lung, ureter, and falciform ligament as well as somatic soft tissues [2–6]. However, PEComa can rarely occur in the bones, in particular the diaphysis of the long bones [7, 8]. PEComas demonstrate both epithelioid and spindle features microscopically. High mitotic activity, focal necrosis, and cytolo
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