It is the most common subtype of rhabdomyoma even
though it remains relatively rare.
Age: Adult rhabdomyomas occur at a mean age of approximately
50 years although there is a wide age range.
have a predilection for the head and neck region.
The most common sites
lesions are the larynx, pharynx, and the floor of the mouth.
Unusual sites include the orbit, stomach,
It is a circumscribed mass (usually less
than 10 cm) whose surface may be coarsely bosselated.
These lesions have a brick-red colour. Occasionally the mass may be multinodular.
There are large
polygonal cells arranged in solid sheets. The most characteristic features
is the deeply eosinophilic cytoplasm.
The cytoplasm may be finely
granular or vacuolated owing to the presence of glycogen.
So-called "spider cells" are formed by thin strands of cytoplasm
separating peripherally placed vacuoles.
In some cases
vacuolization is so prominent so as to produce a microcystic pattern.
The nuclei tend to be small
and round, and located both peripherally and centrally.
Nuclear pleomorphism, hyperchromatism and mitotic figures are generally absent.
cytoplasm often contains cross striations.
In some cells, striations are separated from
each other at regular intervals
perpendicular to the long axis of the cell imitating mature skeletal
muscle, while in others striations are of irregular thickness and
haphazardly placed within the cell.
Histochemical staining with Masson's trichrome or PTAH (phosphotungstic acid hematoxylin)
highlights the cross striations.
Cell vacuoles are
PAS-positive and diastase sensitive.
Cells react with myogenic markers, muscle specific actin,
desmin, smooth muscle actin, myoglobin, as well as vimentin
and occasionally S-100 protein.
Reactivity for cytokeratin,
epithelial membrane antigen, glial fibrillary acidic protein and
generally not found.
Differential diagnosis of Adult Rhabdomyoma:
Granular cell tumour;
Alveolar soft part sarcoma;Paraganglioma;
Malignant melanoma ;