Aims: We report three cases of skeletal muscle regeneration, of which
two mimicked a small round cell tumour, especially a rhabdomyosarcoma.
Methods and results: One case presented as an intramuscular mass, loc
ated in the right quadriceps of a 12-year-old male; the second patient
was a 25-year-old football player who complained of painful left pero
neus muscles: the third patient was a 22-year-old male who underwent a
n amputation of the right thigh 5 days after right leg amputation due
to limb crush. Histologically, muscle biopsy specimens showed a prolif
eration of small round cells, either infiltrating the striated muscle
in a diffuse manner or growing within and around necrotic myofibres. I
mmunohistochemically and ultrastructurally, the cellular population wa
s composed of two types of cells: phagocytic cells the nuclei of which
occasionally showed a wreathlike arrangement around necrotic myofibre
s resulting in structures resembling Langhans-type multinucleated gian
t cells, and proliferating satellite cells showing enlarged nuclei, pr
ominent nucleoli, mitotic figures, myogenic differentiation and fusion
features in order to form regenerating myotubes. Conclusions: Muscle
regeneration is a benign process that may occasionally mimic a small r
ound cell proliferation resembling a lymphoma or an alveolar rhabdomyo
sarcoma with which it should not be confused.