Brain Stem Gliomas overview

# Overview
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. In the era preceding modern imaging, all brainstem gliomas were regarded as a solitary pathological entity with poor prognosis. In the late 1960s, Matson suggested that all brainstem tumors were malignant and were deemed inoperable regardless of their histopathological characteristics or location.This assertion was questioned shortly thereafter by Pool, who was one of the first to report tumor resection in the brainstem, which in the case described was inside the aqueduct. In 1980, Hoffman et. described the dorsally exophytic group of brainstem gliomas as a distinct subgroup, and reported that these lesions were surgically curable with aggressive resection. Brainstem gliomas may be classified into four subtypes: diffuse, focal, dorsal exophytic, and cervicomedullary. Brainstem gliomas may arise from glial cells of the brainstem, a majority of these tumors are found in the pons. Other areas include tectal area and medulla. Genetic mutations in histone genes, activin A receptor gene, tyrosine kinase mutations and TP53 mutations have been implicated in the development of brain stem gliomas. Brainstem gliomas must be differentiated from other brain tumors presenting as headache, visual disturbances, dizziness, paralysis, paresis, pyramidal signs, nausea, vomiting and weight loss. The differentials include medulloblastomas, craniopharyngiomas, ependymoma, pinealoma, meningioma, hemangioblastoma, tuberculous infection, toxoplasmosis and brain metastases. The incidence of brainstem gliomas is estimated to be 0.05 - 0.1 cases per 100,000 individuals in USA. A bimodal distribution by age is noted with peak incidences rates in children and older adults. Brainstem gliomas are commonly found in individuals suffering from Li-Fraumeni syndrome, neurofibromatosis type 1 (NF1), nevoid basal cell carcinoma syndrome, tuberous sclerosis and Turcot syndrome. If left untreated, patients with brainstem gliomas may progress to develop increased intracranial pressure and cerebral herniation. Common complications of brainstem gliomas include loss of motor and sensory functions and loss of regulation of basic body functions like blood pressure, swallowing and respiration. Prognosis is generally good for dorsal exophytic and cervicomedullary brainstem gliomas, and diffuse subtype has the worst prognosis with treatment. The hallmark of brainstem gliomas is the classic triad of ataxia, long tract signs and cranial nerve palsies. Common symptoms include hemiparesis or hemiplegia, unilateral facial nerve palsy, ataxia, vision defect, hearing loss, morning headache or headache that goes away after vomiting, nausea and vomiting, drowsiness, fatigue, and behavioral changes. Less common symptoms include seizure, trouble learning in school, and deterioration of handwriting and speech. Common physical examination findings of diffuse brainstem gliomas include cranial nerve deficit, pyramidal tract signs, and ataxia whereas that of focal gliomas are diplopia, ophthalmoplegia, Parinaud syndrome, loss of accommodation, and light-near dissociation. The presence of facial sensory loss, dysphagia, and dysphonia on physical examination is diagnostic of cervicomedullary brainstem gliomas. On MRI brain, diffuse brainstem glioma is characterized by decreased intensity on T1, heterogenously increased on T2. Focal brainstem glioma is characterized by iso- to hypointense to grey matter on T1, and hyperintense to grey matter on T2. The optimal therapy for brainstem gliomas depends on the subtype and whether it is newly diagnosed or a recurrent tumor. Patients with diffuse brainstem gliomas are treated with radiotherapy and chemotherapy, whereas patients with focal brainstem gliomas are treated with surgical resection with or without radiation therapy and chemotherapy. Surgical intervention is not recommended for the management of diffuse brainstem gliomas. Surgery with or without radiotherapy and chemotherapy is the mainstay of treatment for focal, dorsal exophytic and cervicomedullary brainstem gliomas.

# Historical prospective
In the era preceding modern imaging, all brainstem gliomas were regarded as a solitary pathological entity with poor prognosis. In the late 1960s, Matson suggested that all brainstem tumors were malignant and were deemed inoperable regardless of their histopathological characteristics or location.This assertion was questioned shortly thereafter by Pool, who was one of the first to report tumor resection in the brainstem, which in the case described was inside the aqueduct. In 1980, Hoffman et. described the dorsally exophytic group of brainstem gliomas as a distinct subgroup, and reported that these lesions were surgically curable with aggressive resection. Over the past 3 decades, the treatment of brainstem gliomas has notably progressed as a result of the gradual advancements in microsurgical techniques, sophisticated imaging technology and, most importantly, the availability of MRI. These modalities have revealed that brainstem gliomas are a heterogeneous group of tumors.

# Classification
Brainstem gliomas may be classified into four subtypes: diffuse, focal, dorsal exophytic, and cervicomedullary.

# Pathophysiology
Brainstem gliomas may arise from glial cells of the brainstem, a majority of these tumors are found in the pons. Other areas include tectal area and medulla. Genetic mutations in histone genes, activin A receptor gene, tyrosine kinase mutations and TP53 mutations have been implicated in the development of brain stem gliomas. On gross pathology, brainstem gliomas can be classified into four subtypes: diffuse, focal, dorsal exophytic and cervicomedullary. Each of the four subtypes has its distinct microscopic pathology.

# Differentiating Brain Stem Gliomas From Other Diseases
Brainstem gliomas must be differentiated from other brain tumors presenting as headache, visual disturbances, dizziness, paralysis, paresis, pyramidal signs, nausea, vomiting and weight loss. The differentials include medulloblastomas, craniopharyngiomas, ependymoma, pinealoma, meningioma, hemangioblastoma, tuberculous infection, toxoplasmosis and brain metastases.

# Epidemiology and Demographics
The incidence of brainstem gliomas is estimated to be 0.05 - 0.1 cases per 100,000 individuals in USA. A bimodal distribution by age is noted with peak incidences rates in children and older adults. The prevalence and incidence of brainstem gliomas do not vary by either race or gender

# Risk Factors
Brainstem gliomas are commonly found in individuals suffering from Li-Fraumeni syndrome, neurofibromatosis type 1 (NF1), nevoid basal cell carcinoma syndrome, tuberous sclerosis and Turcot syndrome.

# Screening
Screening for brainstem gliomas is not recommended.

# Natural history, complications and prognosis
If left untreated, patients with brainstem gliomas may progress to develop increased intracranial pressure and cerebral herniation. Common complications of brainstem gliomas include loss of motor and sensory functions and loss of regulation of basic body functions like blood pressure, swallowing and respiration. Prognosis is generally good for dorsal exophytic and cervicomedullary brainstem gliomas, and diffuse subtype has the worst prognosis with treatment.

# Diagnosis

## History and symptoms
The hallmark of brainstem gliomas is the classic triad of ataxia, long tract signs and cranial nerve palsies. Common symptoms include hemiparesis or hemiplegia, unilateral facial nerve palsy, ataxia, vision defect, hearing loss, morning headache or headache that goes away after vomiting, nausea and vomiting, drowsiness, fatigue, and behavioral changes. Less common symptoms include seizure, trouble learning in school, and deterioration of handwriting and speech.

## Physical exam
Common physical examination findings of diffuse brainstem gliomas include cranial nerve deficit, pyramidal tract signs, and ataxia whereas that of focal gliomas are diplopia, ophthalmoplegia, Parinaud syndrome, loss of accommodation, and light-near dissociation. The presence of facial sensory loss, dysphagia, and dysphonia on physical examination is diagnostic of cervicomedullary brainstem gliomas.

## Laboratory findings
There are no diagnostic lab findings associated with brainstem gliomas.

## X-ray
There are no x-ray findings associated with brainstem gliomas.

## CT scan
Head CT scan may be helpful in the diagnosis of brainstem gliomas. CT scan findings of brainstem gliomas vary according to the different subtypes.

## MRI
On MRI brain, diffuse brainstem glioma is characterized by decreased intensity on T1, heterogenously increased on T2. Focal brainstem glioma is characterized by iso- to hypointense to grey matter on T1, and hyperintense to grey matter on T2.

## Echocardiography or ultrasound
There are no echocardiography or ultrasound findings associated with brainstem gliomas.

## Other imaging findings
On angiography, brainstem gliomas is characterized by anterior displacement of basilar artery.

## Other diagnostic studies
Biopsy may be indicated for brain stem tumors that are not diffuse and intrinsic or when there is diagnostic uncertainty based on imaging findings.

# Treatment

## Medical therapy
The optimal therapy for brainstem gliomas depends on the subtype and whether it is newly diagnosed or a recurrent tumor. Patients with diffuse brainstem gliomas are treated with radiotherapy and chemotherapy, whereas patients with focal brainstem gliomas are treated with surgical resection with or without radiation therapy and chemotherapy.

## Surgery
Surgical intervention is not recommended for the management of diffuse brainstem gliomas. Surgery with or without radiotherapy and chemotherapy is the mainstay of treatment for focal, dorsal exophytic and cervicomedullary brainstem gliomas.