Chiasmatic and Hypothalamic Gliomas

Abstract

Chiasmatic and hypothalamic gliomas are childhood tumors, 75 % occurring in the first decade of life, and equally in boys and girls. In children, low-grade astrocytoma is the more frequent type of lesion, and 10–70 % of patients have neurofibromatosis type 1 (NF1). Visual loss with optic atrophy and growth delay are the most common signs. Intracranial hypertension syndrome with hydrocephalus in relation to obstruction of the foramina of Monro is seen in large tumors. Diencephalic syndrome characterized by emaciation, locomotor hyperactivity, euphoria, and alertness can be observed in children younger than 3 years. Optic glioma associated with NF1 is frequently asymptomatic. The precise origin of chiasmatic or hypothalamic gliomas is often impossible to determine mainly in the largest tumors. In patients with NF1, the most common site of involvement is the optic nerve, and the tumor is smaller than in non-NF1 patients. In patients without NF1, the optic chiasm and hypothalamus are the most frequent sites of involvement. The prognosis is variable: half of the tumors of NF1 patients remain stable compared with only 5 % of those of non-NF1 patients. Spontaneous regression can occur, especially in patients with NF1. Optic and hypothalamic gliomas appear as rounded or lobulated solid suprasellar masses hypointense on T1WI and hyperintense on T2WI (Figs. 30.1 and 30.2). Cystic components are much more frequent in patients without NF1. After gadolinium injection, enhancement is variable and often heterogeneous. Nonenhancement of the optic glioma is frequent in NF1 (Fig. 30.3). The enhancement pattern is often variable over time, without any clinical consequences. In the largest tumors, a posterior extension along the optic tracts to the lateral geniculate bodies is usual (Fig. 30.4). Suprasellar extension compressing the third ventricle and foramen of Monro may be responsible for hydrocephalus (Fig. 30.5). Involvement of the intraorbital optic nerve produces an enlargement and tortuosity of the nerve. Two different patterns can be observed. In some cases, the optic nerve is diffusely infiltrated and appears hypointense on T1WI and hyperintense on T2WI, with quite homogeneous enhancement after gadolinium injection. In other cases there is an infiltration of the subarachnoid spaces, sparing the optic nerve itself, with hyperintensity on T2WI and a rim of enhancement around the unaffected nerve. This pattern must be distinguished from the nontumoral enlargement of the subarachnoid spaces with no enhancement, which is frequently observed, particularly in patients with NF1. Optic-hypothalamic gliomas show a profile of choline, N-acetyl aspartate (NAA), and creatine with a choline/NAA ratio of approximately 2.5. At initial MR spectroscopy, aggressive optic or thalamic gliomas have a significantly lower myoinositol peak than the stable tumors. A decrease in myoinositol occurs before clinical and radiological deterioration. Increased permeability on perfusion imaging is suggestive of aggressive tumor. The differential diagnosis of contrast-enhancing hypothalamic glioma includes, in adults, papillary craniopharyngioma, lymphoma, and metastasis; and in children, adamantinous craniopharyngioma and germinoma. In the case of nonenhancing suprasellar mass, a hamartoma of the tuber cinereum can be evoked.