Soft tissue tumors - Adult type rhabdomyoma

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Soft tissue tumors

Skeletal muscle

Adult type rhabdomyoma

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 21 February 2013, last major update November 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Definition
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● Benign tumor of mature skeletal muscle
● Extracardiac rhabdomyomas are divided into fetal, adult (below) and genital histologic types (eMedicine)
● Extracardiac tumors are not associated with tuberous sclerosis
● Some cases may be due to degeneration and regeneration, and not be neoplastic (Am J Surg Pathol 1989;13:791), but see Head Neck 2006;28:275

Clinical description
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● Very rare
● Usually head and neck, particularly oral cavity
● Median age 60 years, 75% male (Hum Pathol 1993;24:608)
● May be multifocal (25%)

Case reports
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● 43 year old man with midline swelling in upper neck (Acta Cytol 2010;54:968)
● Elderly woman with multifocal oral tumor (Arch Pathol Lab Med 1983;107:638)
● 13 cm tumor in extremity (Hum Pathol 2000;31:1074)
● Parapharyngeal tumor (Dysphagia 2008;23:202)

Treatment
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● Excision is curative, but may recur if incompletely excised

Gross description
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● Median 3 cm, circumscribed, soft, tan-red-brown
● Nodular or lobulated

Micro description
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● Well circumscribed, not encapsulated, sheets of large, well differentiated skeletal muscle cells
● Cells are round or polygonal with abundant eosinophilic fibrillar or granular cytoplasm with frequent cross striations and intracytoplasmic rod-like inclusions
● Nuclei are small, round and vesicular, may have prominent nucleoli
● May have spider cells with vacuolated cytoplasm (cells resemble spider webs)
● Variable glycogen and lipid
● No mitotic activity, no atypia

Micro images
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Large closely packed polygonal cells up to 150 microns

Cells have abundant eosinophilic and granular cytoplasm, often with peripheral vacuoles, giving a spiderweb appearance to some cells, nuclei are round with vesicular chromatin and prominent nucleoli

Distinct well demarcated lobules of polygonal cells	Large closely packed polygonal cells up to 150 microns	Haphazardly arranged crystalline material resembling sarcomeric bands	Crystalline material resembles rods
Various images
Actin+	Desmin+

Cytology description
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● Fragments of tumor cells, which are large, polygonal cells
● Cytoplasm is eosinophilic and finely granular, may resemble granular cell tumor, which is S100+, muscle markers- (Diagn Cytopathol 2009;37:483)
● Eccentrically placed nuclei
● Cross striations and inclusions are not conspicuous (Acta Cytol 2010;54:968)

Cytology images
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Parapharyngeal mass

Cohesive syncytial group of cells with abundant cytoplasm (200X Diff- Quick)

Bland round to oval nuclei with smooth borders (1000X OIL Diff- Quick)

Myoglobin immunostain- Strongly positive neoplastic cells (400X Cell block)

Desmin immunostain- Strongly/diffusely positive neoplastic cells (400X Cell block)

Positive stains
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● Muscle specific actin, desmin and myoglobin (100%)
● PAS+, diastase sensitive (detects glycogen)
● PTAH and Masson trichrome highlight cross striations and rod-like inclusions

Negative stains
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● Keratin, EMA, CD68, S100 (or weak)

Electron microscopy description
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● Myofilaments, Z bands, glycogen granules

Differential diagnosis
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● Alveolar soft part sarcoma
● Crystal storing histiocytosis
● Granular cell tumor: no skeletal muscle differentiation, no glycogen, smaller cells have poorly defined cell borders, often overlying pseudoepitheliomatous hyperplasia, S100+
● Hibernoma: no skeletal muscle differentiation, no glycogen
● Paraganglioma: NSE+, synaptophysin+, chromogranin+
● Well differentiated rhabdomyosarcoma

End of Soft tissue tumors > Skeletal muscle > Adult type rhabdomyoma

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