Soft tissue

Skeletal muscle

Rhabdomyoma



Last author update: 1 November 2012
Last staff update: 26 January 2023

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PubMed Search: Rhabdomyoma

Vijay Shankar, M.D.
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Cite this page: Shankar V. Rhabdomyoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueadultrhabdomyoma.html. Accessed January 30th, 2023.
Adult type rhabdomyoma
Definition / general

Clinical features
  • 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

Treatment
  • Excision is curative but may recur if incompletely excised

Clinical images

Contributed by Mark R. Wick, M.D.

Base of tongue, CT



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

Gross images

Contributed by Mark R. Wick, M.D.

Base of tongue



Microscopic (histologic) description
  • 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

Microscopic (histologic) images

Contributed by Mark R. Wick, M.D. and AFIP

Abundant eosinophilic and granular cytoplasm

Distinct well demarcated lobules of polygonal cells

Large closely packed polygonal cells

Haphazardly arranged crystalline material


Crystalline material resembles rods

Various images



Cytology description
  • 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

Images hosted on other servers:

Loose aggregates of cells

Bland round to oval nuclei

Spindle cells



Positive stains

Negative stains

Electron microscopy description
  • Myofilaments, Z bands, glycogen granules

Differential diagnosis
Fetal type rhabdomyoma
Definition / general
  • Rare benign tumor of immature skeletal muscle differentiation, usually in the head and neck
  • Retroauricular in ages 0 - 3 years

Epidemiology

Sites
  • Usually head and neck; post auricular region is the most common site

Case reports

Treatment

Gross description
  • Median 3 - 5 cm
  • Solitary, well circumscribed mass of soft tissue or mucosa
  • Gray-white-tan-pink, soft with glistening cut surface

Microscopic (histologic) description
  • Circumscribed but not encapsulated
  • Myxoid:
    • Bundles or fascicles of immature slender skeletal muscle with delicate cytoplasmic cross striations and thin tapering eosinophilic processes, resembling myotubules at week 7 - 12 of gestation
    • Also undifferentiated round / oval or spindled mesenchymal cells
    • Stroma is myxoid or fibromyxoid
    • Skeletal muscle cells mature towards periphery, may have pseudocambium layer of plasma cells and lymphocytes under mucosal epithelium
  • Cellular:
    • Bundles or fascicles of cells in parallel or plexiform patterns
    • Sparse collagenous or myxoid stroma
    • Cells have variable skeletal muscle differentiation ranging from immature cells of myxoid pattern (but in larger numbers) to ganglion cell-like rhabdomyoblasts with prominent nucleoli or strap cells with abundant basophilic or eosinophilic cytoplasm and prominent cross striations
    • Infiltration of skeletal muscle may make margins difficult to determine
    • Variable glycogen containing vacuoles
    • No / rare mitotic figures

Microscopic (histologic) images

Contributed by Mark R. Wick, M.D. and AFIP
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Immature muscle cells and mesenchymal cells

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Undifferentiated round mesenchymal cells


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Bipolar immature skeletal muscle cells

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Mucosal tumors

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Tumor cells are arranged in fascicles with less stroma

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Immature skeletal muscle cells

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Ganglion cell-like rhabdomyoblasts


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Strap cells

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Ganglion cell-like rhabdomyoblasts

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Base of tongue, juvenile


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Cellular variant

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Various images



Cytology description

Positive stains

Negative stains

Electron microscopy description
  • Hypertrophied Z band material, thick and thin filaments, numerous mitochondria, some with inclusions

Differential diagnosis
Genital type rhabdomyoma
Definition / general
  • Rare benign tumor with skeletal muscle differentiation in vagina, vulva, cervix and rarely urethra, usually seen in middle aged women

Epidemiology
  • Rarely occurs in men in the paratesticular region, epididymis or in the tunica vaginalis of the testis or prostate
  • Mean age is 42 years

Case reports

Treatment
  • Local excision is curative

Gross description
  • Well circumscribed, solitary, up to 3 cm
  • Resembles polyp
  • Covered by smooth mucosa

Microscopic (histologic) description
  • Submucosal, polypoid, well circumscribed, no capsule
  • Haphazard strap-like or round striated muscle fibers in fibrous stroma with dilated vessels
  • Cells have abundant eosinophilic cytoplasm with glycogen, cross striations, longitudinal myofibrils
  • Nucleus is round, vesicular, central and uniform
  • May have binucleated or multinucleated cells
  • No / rare mitotic figures, no cambium layer, no spider cells, no spindle cells or rhabdomyoblasts, no necrosis, no nuclear pleomorphism

Microscopic (histologic) images

AFIP images
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Submucosal proliferation of haphazard skeletal muscle cells



Positive stains

Negative stains

Differential diagnosis
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