A Rare Case of Adult Rhabdomyosarcoma.

BACKGROUND: Rhabdomyosarcoma is a rare, soft tissue malignancy, diagnosed particularly in adults. It commonly metastasizes to the bone marrow. We present a rare case of an adult rhabdomyosarcoma which illustrates the importance of magnetic resonance imaging in identifying early changes in the internal bone structure.

CASE REPORT: A 50-year-old male presented with acute urinary retention. The patient initially had a CT scan of the lumbar spine which only revealed a protrusion of the L5-S1 intervertebral disc and no apparent cause for the patient's symptoms. One week later, an MRI was performed which showed extensive bone marrow metastases throughout the lumbar spine and a soft tissue mass in the lower sacral region. The bony metastases were not evident on the CT scan and the soft tissue mass was out of the coverage area of the CT. Subsequent biopsy of the soft tissue mass was performed and histopathology concluded the tissue to be a rhabdomyosarcoma. Unfortunately, the patient died one week after diagnosis.

CONCLUSIONS: Although adult rhabdomyosarcomas are very rare, this case highlights the advantage of MRI over CT in identifying early changes in the internal bone structure. Therefore, CT should not be relied upon to exclude bony metastases, particularly in the setting of primary cancer with a known tendency to metastasize to the bone marrow.