Medulloblastoma overview

# Overview
Medulloblastoma is a malignant primary brain tumor that originates in either the cerebellum or the posterior cranial fossa. The term medulloblastoma was first used to describe the tumor by Dr. Harvey Cushing, an American neurosurgeon, in 1924. Medulloblastoma may be classified into several subtypes based on the WHO histological classification system (classic vs variant medulloblastoma) and the molecular subtypes classification system (WNT subgroup vs SHH subgroup vs Group 3 medulloblastoma vs Group 4 medulloblastoma). Medulloblastoma arises from the cerebellar stem cells, which are normally involved in the anatomical development of the cerebellum and posterior cranial fossa structures. Medulloblastoma is an invasive and rapidly growing brain tumor which may metastasize to different organs of the body. Genes involved in the pathogenesis of medulloblastoma include CTNNB1 gene, PTCH1 gene, and MLL2 gene. On gross pathology, a pink, solid, and well circumscribed mass is a characteristic finding of medulloblastoma. On microscopic histopathological analysis, round tumor cells, elevated mitotic rate, increased nucleus:cytoplasmic ratio, and Homer-Wright rosettes are characteristic findings of medulloblastoma. Medulloblastoma must be differentiated from other diseases that cause morning headache, recurrent vomiting, nausea, restlessness, and poor feeding among children such as ependymoblastoma, cerebral neuroblastoma, and pineal tumor. Physical examination of patients with medulloblastoma is usually remarkable for strabismus, nystagmus, motor weakness, and ataxia. Common complications of medulloblastoma include hydrocephalus, decerebrate attacks, and cranial nerve palsies. Medulloblastoma is the second most common brain tumor among the pediatric population. Prognosis is generally good, the 5-year survival rate of patients with medulloblastoma is approximately 69%. The staging of medulloblastoma is based on the modified Chang's staging system. Medulloblastoma patients are risk stratified into either standard risk group or high risk group based on the tumor stage, patient's age, and the extent of any previous surgical resection. Brain MRI with gadolinium based contrast is the investigation of choice for the diagnosis of medulloblastoma. On a T1 weighted brain MRI image, medulloblastoma is characterized by a hypointense mass located at the posterior cerebral fossa that may demonstrate calcification and necrosis. According to the risk stratification criterion for medulloblastoma patients, surgery must be followed by the appropriate radiotherapy or chemotherapy management.

# Historical Perspective
The term medulloblastoma was first used to describe the tumor by Dr. Harvey Cushing, an American neurosurgeon, in 1924.

# Classification
Medulloblastoma may be classified into several subtypes based on the WHO histological classification system (classic vs variant medulloblastoma) and the molecular subtypes classification system (WNT subgroup vs SHH subgroup vs Group 3 medulloblastoma vs Group 4 medulloblastoma).

# Pathophysiology
Medulloblastoma arises from the cerebellar stem cells, which are normally involved in the anatomical development of the cerebellum and posterior cranial fossa structures. Medulloblastoma is an invasive and rapidly growing brain tumor which may metastasize to different organs of the body. Genes involved in the pathogenesis of medulloblastoma include CTNNB1 gene, PTCH1 gene, MLL2 gene, SMARCA4 gene, DDX3X gene, CTDNEP1 gene, KDM6A gene, and TBR1 gene. Medullobastomas is associated with a number of syndromes that include Gorlin syndrome and Turcot syndrome. On gross pathology, a pink, solid, and well circumscribed mass is a characteristic finding of medulloblastoma. On microscopic histopathological analysis, round tumor cells, elevated mitotic rate, increased nucleus:cytoplasmic ratio, and Homer-Wright rosettes are characteristic findings of medulloblastoma.

# Causes
There are no established direct causes for medulloblastoma. The development of medulloblastoma is the result of multiple genetic mutations.

# Differentiating Medulloblastoma from other Diseases
Medulloblastoma must be differentiated from other diseases that cause morning headache, recurrent vomiting, nausea, restlessness, and poor feeding among children such as ependymoblastoma, cerebral neuroblastoma, and pineal tumor.

# Epidemiology and Demographics
Medulloblastoma is the second most common brain tumor among the pediatric population. The overall age adjusted incidence rate of medulloblastoma is approximately 0.71 per 100,000 individuals in the United States. The incidence of medulloblastoma decreases with age; the median age at diagnosis is between 5 to 7 years. Males are more commonly affected with medulloblastoma than females. The male to female ratio is approximately 1.44 to 1.

# Risk Factors
There are no established risk factors for medulloblastoma.

# Screening
According to the the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for medulloblastoma.

# Natural History, Complications and Prognosis
If left untreated, patients with medulloblastoma may progress to develop ataxia, nystagmus, and  positional dizziness. Common complications of medulloblastoma include hydrocephalus, decerebrate attacks, and cranial nerve palsies. Prognosis is generally good, the 5-year survival rate of patients with medulloblastoma is approximately 69%.

# Diagnosis

## Staging
The staging of medulloblastoma is based on the modified Chang's staging system. Medulloblastoma patients are risk stratified into either standard risk group or high risk group based on the tumor stage, patient's age, and the extent of any previous surgical resection.

## History and Symptoms
The hallmark of medulloblastoma is morning headache. Other common symptoms of medulloblastoma include recurrent vomiting, restlessness, and frequent falls.

## Physical Examination
Patients with medulloblastoma usually appear restless. Physical examination of patients with medulloblastoma is usually remarkable for strabismus, nystagmus, motor weakness, and ataxia.

## Laboratory Findings
There are no diagnostic lab findings associated with medulloblastoma.

## CT
On head CT scan, medulloblastoma is characterized by a hyperdense mass arising from the cerebellar vermis,  effacement of the fourth ventricle, and dilated ventricles due to  obstructive hydrocephalus.

## MRI
Brain MRI with gadolinium based contrast is the investigation of choice for the diagnosis of medulloblastoma. On a T1 weighted brain MRI image, medulloblastoma is characterized by a hypointense mass located at the posterior cerebral fossa that may demonstrate calcification and necrosis.

## Other Imaging Findings
Magnetic resonance spectroscopy (MR spectroscopy) study for medulloblastoma demonstrates an elevated choline level and a reduced N-acetyl aspartate level. MR spectroscopy study also demonstrates a peak in taurine level.

## Other Diagnostic Studies
Bromodeoxyuridine labeling study may be helpful in the diagnosis of medullblastoma. An elevated bromodeoxyuridine labeling index is suggestive of a rapid growth rate of medulloblastoma.

# Treatment

## Medical Therapy
Risk stratification determines the protocol of management used for medulloblastoma patients. Radiotherapy is the mainstay of treatment for medulloblastoma. Radiotherapy for medulloblastoma must be started within the 6 weeks period following surgery. Adjunctive chemotherapy is also required for the management of certain medulloblastoma patients. Recommended chemotherapeutic regimens used for the management of standard risk medulloblastoma patients include a combination of lomustine AND vincristine AND   cisplatin.

## Surgery
Surgical intervention alone is not recommended as a single therapeutic modality for the management of medulloblastoma. According to the risk stratification criterion for medulloblastoma patients, surgery must be followed by the appropriate radiotherapy or chemotherapy management. Surgical excision of medulloblastoma may be done either via  a posterior fossa craniectomy approach or a suboccipital craniectomy approach. Complications related to surgery may include aseptic meningitis, haematoma formation, and posterior fossa syndrome.