Extracardiac adult‐type rhabdomyoma—Report of two cases in dogs

Abstract

This report describes the cytologic, histopathologic, and immunohistochemical features of adult‐type rhabdomyoma located within the subcutaneous tissue in a 14‐year‐old female Border Collie (thigh) and a 13‐year‐old male Mongrel (flank). In both cases, fine‐needle aspiration biopsy revealed cluster‐forming, epithelial‐like polygonal cells with abundant foamy cytoplasm, and moderate to marked anisocytosis and anisokaryosis; therefore, an epithelial tumor was suspected. After surgical excision, tumors underwent histopathologic examination with additional immunohistochemistry. Both tumors were well‐demarcated and located within the subcutaneous tissue in the vicinity of the cutaneous muscle. The tumor mass consisted of densely packed round or polygonal cells with distinct vacuolation of the cytoplasm. Tumor cells expressed vimentin, desmin, and NSE and were cytokeratin and α‐SMA negative. Based on histologic features and immunophenotyping, adult‐type rhabdomyoma was diagnosed in both cases. This study highlights that the cytologic features of rhabdomyoma can be misleading and may suggest an epithelial tumor.

Fetal rhabdomyoma in a Thoroughbred filly

“…This form of fetal neoplasm is predominantly localised in the head and neck regions (Hansen & Katenkamp, 2005 ; Walsh & Hurt, 2008 ); however, it can occur in a variety of anatomical locations, including the extremities, mediastinum and perianal region (Valdez et al., 2006 ; Walsh & Hurt, 2008 ). Extracardiac examples of rhabdomyoma in the small animal literature include neoplasms located in the larynx, tongue, subcutis of the pinna, extremities and abdomen (Dunbar et al., 2012 ; Meyerholz et al., 2004 ; O'Hara et al., 2001 ; Padźior‐Czapula et al., 2023 ; Reams Rivera & Carlton, 1992 ; Roth, 1990 ).…”

“…Scale bars: A-D = 1 mm.2008). Extracardiac examples of rhabdomyoma in the small animal literature include neoplasms located in the larynx, tongue, subcutis of the pinna, extremities and abdomen(Dunbar et al, 2012;Meyerholz et al, 2004;O'Hara et al, 2001;Padźior-Czapula et al, 2023;Reams Rivera…”