Head and Neck Imaging

Rhabdomyosarcoma, head and neck

malignant tumour of skeletal muscle. This tumour mainly occurs in children. Apart from lymphoma, it is the most common malignant tumour of the head and neck in childhood. Rhabdomyosarcoma is divided into four histological subtypes: embryonal, botryoid, alveolar and pleomorphic; the embryonal and botryoid subtype account for about 90% of primary head and neck lesions. Head and neck rhabdomyosarcoma has three sites of predilection: the orbit, the nasopharynx and paranasal cavities, and the temporal bone.

Orbit

Most lesions originate behind the globe. The bony orbit limits tumour growth, except anteriorly: prooptosis (often rapidly progressive) is a common presenting symptom. The tumour may grow intracranially by posterior extension through the superior orbital fissure or optic canal. Extension into the paranasal sinuses is also possible.

Nasopharynx and paranasal cavities

These tumours are usually large at presentation and nearly always invade neighbouring structures (Fig.1). Otologic symptoms, due to dysfunction of the eustachian tube, are common; other symptoms include nasal obstruction, epistaxis, dysphagia and cranial nerve dysfunction.

Temporal bone

Most commonly, these lesions arise from the mastoid part of the temporal bone. The facial canal is at risk of being invaded, and may serve as a route for perineural tumour spread head and neck (facial nerve palsy (VI:2), Fig. 3). Less commonly, rhabdomyosarcoma arises from the petrous apex (Fig.2); further skull base involvement rapidly produces dysfunction of several cranial nerves.

Other sites

Depending on the location, the rapidly growing mass lesion may produce dysphagia, dyspnoea (larynx, pharynx, oral cavity) or a visible soft tissue mass (scalp, cheek, neck).

Patients with a nasopharyngeal, paranasal or temporal bone rhabdomyosarcoma are at risk of developing meningeal extension, followed by brain involvement and eventually subarachnoidal dissemination to the entire neural axis. Lymphatic spread is rarely seen. Distant metastasis, mainly to the lungs, is detected in about 13% of patients presenting with head and neck rhabdomyosarcoma.

Diagnostic imaging

As the treatment is determined by the local tumour extent and the possible presence of distant disease, imaging should include a CT and/or MRI scan of the primary tumour site and a CT scan of the chest. In patients at risk of developing meningeal extension, a gadolinium-enhanced MR study of the brain should be performed.

Treatment

Surgery is the treatment of choice for small lesions. Larger lesions are often difficult to resect because of anatomical, functional and/or cosmetic restraints in such lesions, irradiation may be the treatment of choice. All patients with head and neck rhabdomyosarcoma receive chemotherapy, as either a post- or presurgical treatment (chemotherapy may convert a large mass into a resectable lesion) or in combination with radiotherapy. Some patients may need a combination of all treatment modalities.

RH

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Fig.2

Six-year-old girl, presenting with right-sided facial nerve paralysis; clinical examination revealed profound sensorineural hearing loss. a, b. Gadolinium-enhanced T1-weighted spin-echo images (a 3 mm caudal to b). Strongly enhancing mass lesion in the right petrous apex (arrow), extending in and over the middle ear cavity (single arrowhead). Large tumoral component (double arrowhead) in the internal auditory canal and bulging into the cerebellopontine angle (presumably perineural spread along facial nerve). The reason for the slight hypersignal within the right labyrinth is unclear (courtesy by Bert De Foer, MD, Antwerp, Belgium).
Rhabdomyosarcoma, head and neck, Fig.1 (a)
Rhabdomyosarcoma, head and neck, Fig.1 (b)
Rhabdomyosarcoma, head and neck, Fig.1 (c)
Rhabdomyosarcoma, head and neck, Fig.2 (a)
Rhabdomyosarcoma, head and neck, Fig.2 (b)