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Clinical Problem Solving: Pathology
June 20, 2011

Pathology Quiz Case 1: Diagnosis

Author Affiliations


Arch Otolaryngol Head Neck Surg. 2011;137(6):638-639. doi:10.1001/archoto.2011.71-b

Rhabdomyosarcoma is a soft-tissue tumor that primarily occurs in children and adolescents, usually appearing before the age of 20 years. Histologically, the rhabdomyoblast is the diagnostic cell in all types of rhabdomyosarcoma. This cell contains eccentric eosinophilic granular cytoplasm with both thin and thick filaments. There are 3 histologic variants of rhabdomyosarcoma: embryonal, alveolar, and pleomorphic. Embryonal rhabdomyosarcoma appears similar to developing embryonic muscle tissue. However, the histologic pattern of embryonal rhabdomyosarcoma is variable, with varying degrees of differentiation.1Common features include differing levels of cellularity across the tumor, primitive round or spindle-shaped cells, cross-striations in 50% to 60% of cases, and a matrix consisting of scant collagen and myxoid stroma.1Genetically, there is frequently a loss of heterozygosity at the short arm of chromosome 11 (11p15.5) or trisomy 8.1In contrast, alveolar rhabdomyosarcoma tends to have either a more uniform cellular distribution or a regular pattern of spaces devoid of cells that resemble alveoli.1The alveolar subtype also has distinct cytogenetic abnormalities, consisting of breaks in the PAX3or PAX7genes and in the FKHRgene on chromosome 2. These breaks result in fusion genes that encode an abnormal transcription factor, and detection of these fusion genes can aid in the diagnosis of the alveolar subtype. Pleomorphic rhabdomyosarcoma, which is more common in adults, consists of pleomorphic rhabdomyoblasts that are large and atypical.1Mutations of p53are also noted in some instances of rhabdomyosarcoma.1

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