Tumours of the skull base

MALIGNANT

CARCINOMA

Carcinoma of the nasopharynx, paranasal sinuses or ear may extend intracranially either by direct erosion or through the skull foramina. It frequently penetrates the dura (in contrast to metastatic carcinoma of the spine) and may involve almost any cranial nerve. Symptoms of nasopharyngeal or sinus disease are often associated with facial pain and numbness. Spread to the CSF pathways leads to carcinomatous meningitis and may cause multiple cranial nerve palsies. Skull X-ray, CT scan and MR I scan will demonstrate a lesion involving the skull base. CT scanning most clearly shows the bone involvement. Treatment is usually restricted to retropharyngeal biopsy plus radiotherapy.

CHORDOMA

Rare tumours of notochordal cell rests arising predominantly in the sphenoido-occipital (clivus) and sacrococcygeal regions. Although growth begins in the midline, they often expand asymmetrically into the intracranial cavity. Chordomas may present at any age, but the incidence peaks in the 4th decade. They are locally invasive and rarely metastasise.

Clinical: most patients develop nasal obstruction. Cranial nerve palsies usually follow and depend on the exact tumour site. Skull X-ray shows a soft tissue mass with an osteolytic lesion of the sphenoid, basi-occiput or petrous apex. CT scan confirms the presence of a partly calcified mass causing marked bone destruction and extending into the nasopharyngeal space.

MRl scan more clearly demonstrates the structural relationships. Management: the tumour site prevents complete removal. Usually extensive debulking (sometimes through the transoral route) is combined with radiotherapy. Most patients die within 10 years of the initial presentation.

BENIGN

GLOMUS JUGULARE TUMOUR (syn: chemodectoma, paraganglioma)

Rare tumour arising from chemoreceptor cells in the jugular bulb or from similar cells in the middle ear mucosa. This tumour extensively erodes the jugular foramen and petrous bone; many patients present with cranial nerve palsies, especially IX-XII. Chemodectomas occasionally arise at other sites and metastasis may occur. X-ray and CT scan demonstrate an osteolytic lesion expanding the jugular foramen. MRl shows the anatomical relationships.

Angiography reveals a vascular tumour, usually only filling from the external carotid artery, but occasionally from vertebral branches.

Management: tumour vascularity makes excision difficult. Selective embolisation may considerably reduce the operative risks or provide an alternative treatment. The value of radiotherapy is uncertain.

OSTEOMA

Rare tumours, usually occurring in the frontal sinus and eroding into the orbit, nasal cavity or anterior fossa. If sinus drainage becomes obstructed, a mucocele develops, often with infected contents. These lesions require excision, cither through an ethmoidal approach or through a frontal craniotomy.

Chordoma -sites of intracranial origin

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