Rhabdomyosarcoma is a malignant tumour with skeletal muscle cell morphology. It is one of the tumours of muscular origin.
This article focuses on a general discussion of rhabdomyosarcomas. For location specific details, please refer to:
- rhabdomyosarcomas of the biliary tract
- rhabdomyosarcomas of the genitourinary tract
- rhabdomyosarcoma of the heart
- rhabdomyosarcomas of the head and neck
- rhabdomyosarcomas of the orbit
Rhabdomyosarcomas are the most common soft tissue tumour in children and account for 5-8% of childhood cancers 6-7, and 19% of all paediatric soft tissue sarcomas 7.
In general, they are found in young patients, less than 45 years of age 6, with ~65% diagnosed in patients under 10 years old 7.
There is a slight male predilection (M:F 1.67:1 7) with Caucasian children affected more often than children of other races.
Clearly, clinical presentation will vary depending on the location of the tumour (see below); however, in general, rhabdomyosarcomas are rapidly growing masses. They cause localised pressure effects on neurovascular structures and have a predilection for infiltrating bones 6. Pathological fractures could therefore occur.
These tumours can occur anywhere, and not necessarily where skeletal muscle is normally found. In children and adolescents, they occur predominantly in the head, neck and pelvis.
Rhabdomyosarcomas are found essentially anywhere in the body 4,7:
- head and neck: ~50% *
- orbit: ~20%
- oropharynx/nasopharynx, palate: ~15%
- sinuses, mastoid, middle ear: ~15%
- genito-urinary: ~25%
- paratesticular: ~20%
- bladder: ~5%
- extremities: ~15%
- other: ~10%
- trunk and thorax: 7%
- gastrointestinal tract: 1%
*: see note on figures/percentages
Rhabdomyosarcomas are thought not to arise from skeletal muscle, but rather to differentiate into a tumour which resembles skeletal muscle 7. This accounts for it arising in locations where no skeletal muscle is present. It is divided into three subtypes 6-7:
- embryonal rhabdomyosarcoma
- alveolar rhabdomyosarcoma: 20%
- pleomorphic rhabdomyosarcoma: 5%
Although the vast majority of cases are sporadic, increased incidence of rhabdomyosarcomas is seen in patients with a variety of syndromes and congenital anomalies, including 7:
- neurofibromatosis type I (NF1)
- Beckwith-Wiedemann syndrome
- Li-Fraumeni syndrome
- Costello syndrome
- maternal use of cocaine and marijuana
Please refer to Rhabdomyosarcoma staging.
Unfortunately, the appearance of the mass itself is non-specific and indistinguishable from other sarcomas. The location and demographics of the patient are most useful in narrowing the differential.
Although entirely non-specific plain films are a useful first step as they can give a quick global view of the region and identify calcifications in the mass, bony involvement and metastases. The mass appears of soft tissue density.
When present in the extremities in children, embryonal rhabdomyosarcomas may cause bowing of the adjacent long bones. This should not be thought of as suggesting slow growth or indolent behaviour 6.
- heterogeneous well-defined irregular mass of low to medium echogenicity
- soft tissue density
- some enhancement with contrast
- adjacent bone destruction is seen in over 20% of cases 6
Signal characteristics include:
- low to intermediate intensity, isointense to adjacent muscle
- areas of haemorrhage are common in alveolar and pleomorphic subtypes
- prominent flow voids may be seen particularly in extremity lesions 7
- T1 C+ (Gd): shows considerable enhancement
Embryonal rhabdomyosarcomas tend to be more homogeneous, whereas alveolar and pleomorphic rhabdomyosarcomas frequently have areas of necrosis 6. The later also has a predilection of ring-like enhancement 6.
Treatment and prognosis
Unfortunately, up to 20% of patients have metastases at the time of diagnosis 7. These are typical to lung and bone marrow.
Treated with combination surgery, chemotherapy, and radiation:
- surgery: resection of the primary tumour, if necessary after down-staging chemoradiotherapy
- chemotherapy: common agents include vincristine, cyclophosphamide, dactinomycin, adriamycin, ifosfamide, VP-16
- radiotherapy: external beam radiation is used in some cases of rhabdomyosarcoma
Survival varies dependent on primary location, histological type, local invasion and metastases. Overall 5-year survival is in the region of 75% 7.
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