Brain Stem Gliomas

Background: Brainstem gliomas are tumors that occur in the region of the brain referred to as the brain stem, which is the area between the aqueduct of Sylvius and the fourth ventricle. Although various systems are used to classify these tumors, the authors have divided brainstem gliomas into 3 distinct anatomic locations—diffuse intrinsic pontine, tectal, and cervicomedullary. Intrinsic pontine gliomas carry a grave prognosis. Longer survival is associated with the tectal and cervicomedullary gliomas. Tumors also are characterized on the basis of site of origin, focality, direction and extent of tumor growth, degree of brainstem enlargement, degree of exophytic growth, and presence or absence of cysts, necrosis, hemorrhage, and hydrocephalus.

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Pathophysiology: These tumors have a predilection to originate from the left side. Most are located in the pons; however, medulla and midbrain may be involved as well. Brainstem gliomas are highly aggressive brain tumors. Anatomic location determines the pathophysiological manifestation of the tumor. With tectal lesions, hydrocephalus may occur as a result of fourth ventricular compression. With pontine and cervicomedullary lesions, cranial nerve or long tract signs are observed commonly.

Frequency:

In the US: Brainstem gliomas have been reported to make up 2.4% of all intracranial tumors in adults and 9.4% of intracranial tumors in children. Brainstem gliomas account for approximately 10-20% of all childhood brain tumors. The incidence in adults is lower than that in children younger than 16 years. A tendency for brainstem gliomas to follow a more indolent course in adults than in children has been noted; in adults, these tumors are more likely to be low grade and remain localized. Mortality/Morbidity:

Morbidity is due to the location of the space-occupying lesion and compression of surrounding structures; because these structures regulate basic body functions of blood pressure, respiration, and swallowing as well as motor and sensory functions, compression can produce substantial neurological disability. Sudden death can result from increased intracranial pressure and subsequent cerebral herniation. This may be a consequence either of edema induced by the tumor or of hemorrhage into the neoplasm. Race: CNS tumors vary in incidence by age, sex, ethnic group, and country, and also over time. How much of this variation is due to artifactual influences or etiologic differences has been the subject of many debates.

Sex: Some reports have suggested a slight male preponderance, whereas others have failed to observe any sex predilection.

Age:

Bimodal age distribution has been noted, with a peak incidence in the latter half of the first decade of life and a second peak in the fourth decade. Approximately three fourths of patients are younger than 20 years. Neoplasms of the brain stem have been identified in children younger than 1 year.

History:

Common presenting symptoms include double vision, weakness, unsteady gait, difficulty in swallowing, dysarthria, headache, drowsiness, nausea, and vomiting. Rarely, behavioral changes or seizures may be seen in children. Older children may have deterioration of handwriting and speech. Pontine lesions usually present with any or all of the above signs and symptoms, depending on location and extension. Midbrain and lower brainstem/upper spinal cord signs and symptoms may be seen with extension of the neoplasm to involve these structures. In infants and children presenting with failure to thrive, pontine glioma should be considered in the differential diagnosis. Tectal lesions typically present with headache, nausea, and vomiting. Hydrocephalus is a common presentation, especially for tumors in periaqueductal or fourth ventricle outflow locations, because these regions have less tolerance of growth and higher risk of obstructive hydrocephalus. Cervicomedullary lesions usually present with dysphagia, unsteadiness, nasal speech, vomiting, and weakness. Physical:

Common clinical findings can be summarized as constituting a triad of cranial nerve deficits, long tract signs, and ataxia (of trunk and limbs). Papilledema may be seen. Sixth and seventh cranial nerves are involved commonly. Facial sensory loss and a primary position, upbeating nystagmus may be seen. Involvement of cranial nerve III or IV suggests a mesencephalic component. Tectal lesions may present with diplopia reflecting an internuclear ophthalmoplegia, indicating involvement of the medial longitudinal fasciculus. Parinaud syndrome also may be seen, with paralysis of upward gaze and accommodation, light-near dissociation (loss of pupillary reflex to light with preservation of pupilloconstriction in response to convergence), eyelid retraction, and convergence-retraction nystagmus. Cervicomedullary lesions may present with sensory loss of the face (involvement of the trigeminal nucleus), dysphagia and/or dysphonia from lower cranial nerve involvement (commonly IX and X), long tract signs, and ataxia. Downbeating nystagmus and oculomyoclonus often are seen with medullary involvement. Causes:

Although no familial tendency is prominent overall, an increased incidence of brainstem glioma has been observed consistently in patients with neurofibromatosis (up to 14% in some reports). Thus far, no genetic or molecular markers have been recognized for brainstem gliomas. In children irradiated for tinea capitis, an increased incidence of CNS tumors, especially meningiomas, gliomas, and nerve sheath tumors, has been reported. No specific reference is made in these reports to tumors of the brain stem. Radiotherapy-induced neoplasms tend to be more aggressive in their natural history than their de novo counterparts.