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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other

Adult type rhabdomyoma

Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.

Revised: 22 July 2009, last major update July 2009

Copyright: (c) 2002-2009, 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

● 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

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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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● 13 cm tumor in extremity (Hum Path 2000;31:1074)

● Elderly woman with multifocal oral tumor (Archives 1983;107:638)

● Parapharyngeal tumor (Dysphagia 2008;23:202)

Treatment and prognosis

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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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Distinct well demarcated lobules                  Large closely packed polygonal cells

of 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

Cells usually have haphazardly                      Crystalline material

arranged crystalline material                         resembles rods

resembling sarcomeric bands

Other images: large closely packed polygonal cells up to 150 microns #1;  #2;  actin+;  desmin+

Cytology description

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● Cytoplasm is eosinophilic and finely granular, may resemble granular cell tumor, which is S100+, muscle markers- (Diagn Cytopathol 2009;37:483)

Cytology images

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Parapharyngeal mass

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

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● Myofilaments, Z bands, glycogen granules

Differential diagnosis

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● 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

● Well differentiated rhabdomyosarcoma

● Crystal storing histiocytosis
● Alveolar soft part sarcoma

References

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● eMedicine

End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Adult type rhabdomyoma

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