Rhabdomyosarkom des Zungengrunds

Rhabdomyosarkom Radiopaedia • CC-by-nc-sa 3.0 • de

Rhabdomyosarcoma (RMS) is a malignant tumor with skeletal muscle cell morphology. It is one of the tumors of muscular origin.

This article focuses on a general discussion of rhabdomyosarcomas. For location specific details, please refer to:

Epidemiology

Rhabdomyosarcomas are the most common soft tissue tumor in children and account for 5-8% of childhood cancers, and 19% of all pediatric soft tissue sarcomas .

In general, they are found in young patients, less than 45 years of age , with ~65% diagnosed in patients under 10 years old .

There is a slight male predilection (M:F 1.67:1 ) with Caucasian children affected more often than children of other races.

Clinical presentation

Clearly, clinical presentation will vary depending on the location of a tumor (see below); however, in general, rhabdomyosarcomas are rapidly growing masses. They cause localized pressure effects on neurovascular structures and have a predilection for infiltrating bones . Pathological fractures could therefore occur.

These tumors can occur anywhere, and not necessarily where the skeletal muscle is normally found. In children and adolescents, they occur predominantly in the head, neck and pelvis.

Distribution

Rhabdomyosarcomas are found essentially anywhere in the body :

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

Pathology

Rhabdomyosarcomas are thought not to arise from skeletal muscle, but rather to differentiate into a tumor which resembles skeletal muscle . This accounts for it arising in locations where no skeletal muscle is present. It is divided into three subtypes :

embryonal rhabdomyosarcoma

spindle cell rhabdomyosarcoma: 50-66%
botryoid rhabdomyosarcoma: 5-10% (best prognosis)
anaplastic rhabdomyosarcoma

alveolar rhabdomyosarcoma: 20%

pleomorphic rhabdomyosarcoma: 5%

Associations

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 :

Staging

Please refer to Rhabdomyosarcoma staging.

Radiographic features

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.

Plain radiograph

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 behavior .

Ultrasound

heterogeneous well-defined irregular mass of low to medium echogenicity

CT

soft tissue density
some enhancement with contrast
adjacent bone destruction is seen in over 20% of cases

MRI

Signal characteristics include:

T1
- low to intermediate intensity, isointense to adjacent muscle
- areas of hemorrhage are common in alveolar and pleomorphic subtypes
T2
- hyperintense
- prominent flow voids may be seen particularly in extremity lesions
T1 C+ (Gd): shows considerable enhancement

Embryonal rhabdomyosarcomas tend to be more homogeneous, whereas alveolar and pleomorphic rhabdomyosarcomas frequently have areas of necrosis . The latter is associated with ring-like enhancement .

Treatment and prognosis

Unfortunately, up to 20% of patients have metastases at the time of diagnosis . These are typical to lung and bone marrow.

Treated with combination surgery, chemotherapy, and radiation:

surgery: resection of a primary tumor, 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 approximately 75% .