Rhabdomyoma

 Adult, fetal, and genital types






Etiology/Pathogenesis




• No association with tuberous sclerosis (unlike cardiac type)

• Some fetal rhabdomyomas associated with nevoid basal cell carcinoma syndrome (Gorlin syndrome)


Clinical Issues




• Fetal type: Usually infants and children

• Adult and genital types: Most common in adults

• Genital type shows strong female predilection

• Adult and fetal types most common in head and neck region

• Genital lesions mostly in vagina, occasionally vulva or cervix

• Excellent prognosis after complete excision


Macroscopic




• Median: ~ 3 cm


Microscopic




• No significant atypia or necrosis; mitoses usually absent
• Fetal rhabdomyoma

image Classic (immature) type: Bland spindle cells in abundant myxoid stroma

image Intermediate (juvenile) type: Increased cellularity with more skeletal muscle differentiation

• Adult rhabdomyoma
image Large polygonal cells with eosinophilic cytoplasm

image Intracytoplasmic cross striations or rod-like inclusions

• Genital rhabdomyoma
image Hypocellular proliferation of bland spindle cells and mature rhabdomyoblastic elements

image Lacks cellular, subepithelial cambium layer


Ancillary Tests




• Desmin (+), myogenin (+), MYOD1(+)


Top Differential Diagnoses




• Carcinoma or melanoma

• Granular cell tumor

• Hibernoma

image
Adult Rhabdomyoma
High magnification shows adult rhabdomyoma composed of large polygonal cells with copious eosinophilic cytoplasm (varying in staining intensity) and small round nuclei with uniform nucleoli.


image
Fetal Rhabdomyoma
Intermediate magnification shows fetal rhabdomyoma of classic (immature) type. Slender spindle cells form loosely organized fascicles in myxoid stroma. Note the absence of pleomorphism and necrosis.

image
Desmin Expression in Rhabdomyoma
Desmin stain in an adult rhabdomyoma shows strong, diffuse positivity throughout the lesion. This is a typical finding in rhabdomyoma and can also highlight cross striations.

image
Myogenin Expression in Rhabdomyoma
Positive myogenin in an adult rhabdomyoma shows immunoreactivity in the nuclei of many of the lesional cells. This is diagnostic of skeletal muscle differentiation. Cytoplasmic staining is sometimes seen, but it is nonspecific. MYOD1 is also useful, although less sensitive.


TERMINOLOGY


Definitions




• Benign tumor with skeletal muscle differentiation

• Extracardiac rhabdomyoma includes adult, fetal, and genital types


ETIOLOGY/PATHOGENESIS


Developmental Anomaly




• No association with tuberous sclerosis (unlike cardiac type)
• Some fetal rhabdomyomas associated with nevoid basal cell carcinoma syndrome (Gorlin syndrome)

image PTCH1 gene mutations


CLINICAL ISSUES


Epidemiology




• Incidence
image Rare

• Age
image Fetal type
– Infants and children (particularly in 1st year of life)

image Adult and genital types
– Most common in adults (mean: 50 years)

• Sex
image Adult and fetal types: Male predilection

image Genital type: Strong female predilection


Site




• Rarely cutaneous lesion
• Adult and fetal types are most common in head and neck region

image Larynx, oropharynx, mouth, neck

• Genital lesions are subepithelial
image Mostly in vagina, occasionally in vulva or cervix

image Rarely in paratesticular region or epididymis

Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Rhabdomyoma

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