Rhabdomyosarcoma accounts for 10% to 15% of all childhood solid tumors. The median age at presentation is 5 years. This aggressive tumor may occur in multiple sites and may arise at any anatomical site, even in regions where striated muscle is not normally present. From 35% to 50% of embryonal rhabdomyosarcomas originate in the head and neck. Origin in the pelvic region is also common. One third of tumors arise within striated muscle of the extremities and trunk. Metastatic disease and recurrence often occur. Metastases are found in the lung, lymph nodes, mediastinum, brain, liver, and skeleton. Therapy consists of surgical removal of the tumor, with adjunctive chemotherapy and radiation therapy for patients with gross or microscopic residual disease.

As with most soft tissue tumors, the MR appearance of rhabdomyosarcoma has anecdotally been reported as intermediate signal intensity (equal to muscle) on T1-weighted images and bright signal intensity on T2-weighted images. However, no known MR criteria can reliably distinguish rhabdomyosarcoma from most other soft tissue tumors of childhood. Therefore, the major role of MRI is pretherapeutic and posttherapeutic tumor staging.

The American Joint Committee on Cancer task force on soft tissue sarcomas determined that histologic grade, and tumor size and depth are essential for a meaningful staging system.

Stage (see notes at bottom)    Overall survival

I = low grade(1), superficial(2)            98.79%
a.   Small(3)
b.   Large

II = 81.80%                     
a.   Low grade, large, deep
b.   High grade(4), small, superficial or deep
c.   High grade, large, superficial

III = high grade, large, deep            51.65%

IV = any metastasis or positive lymph node      -------

(1) Low grade = well or moderately differentiated
(2) Superficial = above the uninvolved superficial fascia
(3) Small = < 5cm in greatest dimension
(4) High grade = poorly or undifferentiated
Data from Memorial Sloan Kettering Cancer Center, 1992.