Overview
Definition:
Posterior fossa tumors are a group of neoplasms located in the infratentorial compartment of the brain, comprising approximately 30-50% of all pediatric brain tumors
These tumors often arise from structures within the cerebellum, brainstem, or fourth ventricle
Common types include pilocytic astrocytoma, medulloblastoma, ependymoma, and atypical teratoid/rhabdoid tumors (AT/RT).
Epidemiology:
These tumors are the most common solid tumors in children and the second most common group of childhood tumors after leukemias
Incidence peaks between ages 5-9 years
Medulloblastoma is the most frequent malignant posterior fossa tumor, while pilocytic astrocytoma is the most common overall posterior fossa tumor in children
Male predominance is noted for medulloblastoma.
Clinical Significance:
Early recognition of posterior fossa tumors is critical due to their propensity for rapid growth and the potential for significant neurological sequelae
Their location poses risks of obstructing cerebrospinal fluid (CSF) flow, leading to hydrocephalus and increased intracranial pressure (ICP), which can rapidly cause irreversible neurological damage if not addressed promptly
Timely diagnosis and management significantly impact prognosis and functional outcomes.
Clinical Presentation
Symptoms:
Headache, often worse in the morning or with positional changes
Nausea and vomiting, typically projectile and without preceding nausea
Gait disturbance, presenting as ataxia or unsteadiness
Cranial nerve palsies, particularly affecting cranial nerves V, VII, IX, X, XI, and XII, leading to facial weakness, dysphagia, or vocal changes
Lethargy and irritability, especially in younger children
Visual changes, such as diplopia or blurred vision due to papilledema or involvement of visual pathways
Developmental regression or loss of previously acquired milestones.
Signs:
Papilledema on funduscopic examination indicating increased ICP
Ataxia, nystagmus, or dysmetria on neurological examination
Cranial nerve deficits manifesting as facial asymmetry, ptosis, or impaired swallowing
Macrocephaly in infants due to hydrocephalus
Signs of meningeal irritation if leptomeningeal spread has occurred
Poor head control or opisthotonus in infants
Irritability or decreased level of consciousness.
Diagnostic Criteria:
Diagnosis is primarily based on neuroimaging findings, confirmed by histopathological examination of tumor tissue
Clinical suspicion, especially in the presence of a constellation of neurological symptoms and signs, mandates urgent investigation
There are no strict numerical diagnostic criteria, but the presence of a space-occupying lesion in the posterior fossa on MRI with characteristic clinical presentation is highly suggestive.
Diagnostic Approach
History Taking:
Detailed history focusing on the onset, duration, and progression of symptoms
Specific questions about morning headaches, vomiting patterns, and changes in gait or coordination
Inquire about any recent falls or trauma that might be confused with tumor symptoms
Assess for recent behavioral changes, lethargy, or developmental delays
Family history of brain tumors or genetic syndromes should be elicited
Red flags include persistent, worsening headaches, unexplained vomiting, new-onset ataxia, and rapid deterioration in neurological status.
Physical Examination:
Comprehensive neurological examination is paramount
Assess the child's growth parameters and head circumference
Evaluate for papilledema using funduscopy
Test cranial nerves thoroughly, looking for deficits
Assess motor strength, tone, and reflexes
Evaluate cerebellar function through tests like finger-to-nose, heel-to-shin, and rapid alternating movements
Assess gait and coordination
Perform a complete systemic examination to rule out metastatic disease or primary systemic conditions.
Investigations:
Magnetic Resonance Imaging (MRI) of the brain with and without contrast is the investigation of choice, providing excellent detail of posterior fossa structures and tumor characteristics
Computed Tomography (CT) scan may be used in emergent situations for rapid assessment of hydrocephalus or calcification
Cerebrospinal fluid (CSF) analysis may be indicated for tumor markers, cytology (especially for medulloblastoma), and to rule out leptomeningeal spread
Complete blood count, electrolytes, and coagulation profiles are essential pre-operatively
Tumor markers like AFP and beta-hCG are important for germ cell tumors and some types of medulloblastoma.
Differential Diagnosis:
Other posterior fossa masses such as cerebellar abscess, arachnoid cysts, hemangioblastomas, or metastatic lesions
Non-neoplastic causes of increased ICP like pseudotumor cerebri (rare in children)
Congenital anomalies affecting the posterior fossa
Brainstem encephalitis or demyelinating lesions
Abscesses should be considered in cases with fever and rapid onset of symptoms
Arachnoid cysts typically have no contrast enhancement and fluid-signal on MRI.
Management
Initial Management:
Immediate management focuses on relieving increased intracranial pressure
Ventricular or subarachnoid peritoneal shunting may be required to manage hydrocephalus
Steroids (e.g., dexamethasone) can be used to reduce peritumoral edema and alleviate symptoms, but their use should be judicious and closely monitored due to potential side effects.
Surgical Management:
Surgical resection is the cornerstone of treatment for most posterior fossa tumors
The goal is maximal safe resection, aiming for gross total removal whenever possible, which is often curative for benign tumors like pilocytic astrocytoma and significantly improves prognosis for malignant tumors
Approaches include suboccipital craniotomy, retrosigmoid approach, or telovelar approach, depending on the tumor location and surgeon preference
Resection aims to debulk the tumor, relieve CSF obstruction, and obtain tissue for definitive histopathological diagnosis.
Medical Management:
Chemotherapy is a critical component of adjuvant or neoadjuvant therapy for malignant posterior fossa tumors, particularly medulloblastoma and ependymoma, and for residual disease after surgery
Specific chemotherapy regimens are tailored to tumor histology, grade, molecular subtype, and patient age
Radiation therapy is also a crucial modality, especially for malignant tumors, often delivered to the posterior fossa and sometimes craniospinal axis.
Supportive Care:
Comprehensive supportive care includes vigilant neurological monitoring, pain management, nutritional support, and physical, occupational, and speech therapy
Management of treatment-related side effects like nausea, vomiting, mucositis, and myelosuppression is essential
Psychological support for the child and family is vital throughout the treatment journey
Regular follow-up with neuro-oncology teams is mandatory.
Complications
Early Complications:
Cerebrospinal fluid leak
Infection (meningitis, wound infection, shunt infection)
Hemorrhage into the tumor or surgical bed
Postoperative hydrocephalus requiring shunting
Cranial nerve palsies persisting after surgery
Cerebellar mutism (a specific syndrome characterized by apathy, mutism, and emotional lability).]
Late Complications:
Recurrence or progression of the tumor
Long-term neurological deficits including motor, sensory, or cognitive impairments
Endocrine dysfunction due to pituitary stalk or hypothalamic involvement
Hearing loss, especially after radiation therapy
Secondary malignancies due to chemotherapy or radiation
Growth retardation
Impact on academic performance and social functioning.
Prevention Strategies:
Meticulous surgical technique to minimize cranial nerve injury and achieve safe resection
Prophylactic antibiotics if indicated
Judicious use of steroids to minimize edema and subsequent complications
Early recognition and management of hydrocephalus
Careful planning of radiation therapy fields to spare critical structures
Comprehensive rehabilitation services to address long-term deficits.
Prognosis
Factors Affecting Prognosis:
Tumor histology (benign vs
malignant)
Histological grade
Extent of surgical resection (gross total resection is favorable)
Presence of metastases
Molecular markers (e.g., for medulloblastoma subtypes)
Age at diagnosis (younger children can have poorer outcomes for some tumors)
Response to chemotherapy and radiation therapy.
Outcomes:
Prognosis varies significantly by tumor type
Benign tumors like pilocytic astrocytoma with gross total resection have excellent long-term survival rates (over 90%)
Malignant tumors like medulloblastoma have a 5-year survival rate ranging from 50-80% depending on risk stratification
Ependymomas have a 5-year survival of about 60-70%
Outcomes are improving with advancements in surgical techniques, radiation delivery, and targeted therapies.
Follow Up:
Long-term follow-up is essential, typically involving regular clinical assessments, neurological examinations, and serial neuroimaging (MRI) for many years post-treatment to monitor for tumor recurrence or late treatment effects
Endocrine assessments, audiology evaluations, and neurocognitive assessments are also part of the comprehensive follow-up plan.
Key Points
Exam Focus:
Posterior fossa tumors are the most common primary brain tumors in children
Early signs of increased intracranial pressure (headache, vomiting, papilledema) are crucial red flags
Hydrocephalus is a common complication due to obstruction of CSF pathways, often leading to macrocephaly in infants and vomiting/headache in older children
Medulloblastoma is the most common malignant posterior fossa tumor
pilocytic astrocytoma is the most common benign one
MRI with contrast is the gold standard for diagnosis.
Clinical Pearls:
Always consider a posterior fossa tumor in a child presenting with unexplained, persistent vomiting or progressive ataxia
A subtle morning headache that improves through the day, especially when associated with vomiting, is highly suspicious
Never dismiss parental concerns about changes in their child's behavior or development – they are often the first to notice subtle signs
Differentiating symptoms of increased ICP from other conditions like gastroenteritis or migraines requires vigilance.
Common Mistakes:
Attributing symptoms of increased ICP to common childhood illnesses without adequate investigation
Delaying neuroimaging in children with persistent neurological signs
Underestimating the severity of symptoms like recurrent vomiting or progressive gait disturbance
Failing to perform a complete neurological examination, including funduscopy, in a child with concerning symptoms
Not considering leptomeningeal spread in the differential diagnosis for medulloblastoma.