Posterior-fossa tumours

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

The posterior fossa lies below the tentorium and contains structures essential for consciousness, ventilation, swallowing, balance and cerebrospinal-fluid flow. Tumours arise from cerebellum, brainstem, ventricular lining, cranial nerves or meninges, or arrive as metastases. Because the fourth ventricle and aqueduct are nearby and compliance is limited, deterioration from obstructive hydrocephalus can be rapid. The immediate task is therefore to recognise physiology before naming histology.

Cerebellar hemisphere disease tends to produce ipsilateral limb dysmetria and intention tremor; vermian disease produces truncal and gait instability. Brainstem or cerebellopontine-angle involvement can cause diplopia, facial weakness or numbness, hearing loss, dysphagia and long-tract signs. Vomiting may be prominent, particularly in children, and can be mislabelled as gastrointestinal or migraine. Papilloedema supports raised pressure but can be absent early, so drowsiness, repeated vomiting or new cranial-nerve signs must drive urgency.

Age is a major diagnostic boundary rather than a shortcut to one answer. Important childhood posterior-fossa entities include medulloblastoma, pilocytic astrocytoma and ependymoma. NCI PDQ describes posterior-fossa ependymoma commonly around the fourth ventricle and presenting with obstructive hydrocephalus, ataxia, neck pain or cranial-nerve palsies. Medulloblastoma is an embryonal tumour with molecularly defined subgroups and potential CSF dissemination. Adult posterior-fossa lesions include metastasis, meningioma, vestibular schwannoma, haemangioblastoma and adult primary CNS tumours. None can be diagnosed reliably from age and location alone.

Management is organised around stabilisation, high-quality MRI, tissue and molecular diagnosis, and a specialist MDT. Surgical goals differ: a circumscribed cerebellar tumour may be removed safely, whereas a lesion adherent to the floor of the fourth ventricle or infiltrating the brainstem may make aggressive resection neurologically destructive. Neuraxis staging is relevant for entities with CSF dissemination, such as medulloblastoma and ependymoma, but is not a universal test for every adult posterior-fossa mass. Children need paediatric neuro-oncology expertise because radiotherapy, chemotherapy and late neuroendocrine or cognitive effects vary strongly with age.

Key points

The posterior fossa contains cerebellum, brainstem, fourth ventricle and lower cranial nerves; little spare volume means a modest lesion can cause early CSF obstruction or brainstem compromise.
Presentation combines cerebellar signs, cranial-nerve dysfunction and raised-pressure features: gait or truncal ataxia, dysmetria, nystagmus, dysarthria, diplopia, vomiting and headache.
Age changes probability and treatment: childhood medulloblastoma, pilocytic astrocytoma and ependymoma are important entities, whereas adults more often have metastasis and extra-axial or cranial-nerve tumours, but imaging and tissue establish diagnosis.
Use urgent CT for rapid detection of hydrocephalus, haemorrhage and major mass effect in deterioration; obtain contrast MRI brain for anatomical and treatment definition, with neuraxis staging only when the suspected entity requires it.
Emergency CSF diversion and tumour surgery are separate decisions. Stabilise acute hydrocephalus, then plan maximal safe tissue diagnosis or resection around brainstem, peduncles, cranial nerves and tumour biology.
Paediatric adjuvant therapy is entity-, molecular-risk- and age-specific: medulloblastoma commonly uses surgery plus risk-adapted chemotherapy and, in older children, radiotherapy; childhood ependymoma and glioma follow different pathways.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Childhood primary tumours

Medulloblastoma, pilocytic astrocytoma and ependymoma are important paediatric posterior-fossa entities with distinct molecular and therapeutic pathways.

Adult lesions

Metastasis, meningioma, vestibular schwannoma, haemangioblastoma and glial tumours form a different adult differential that requires tissue-aware assessment.

Inherited predisposition

Syndromes such as von Hippel–Lindau can predispose to haemangioblastomas and require family history, genetic counselling and systemic context.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
CSF obstruction
Compression of the fourth ventricle or aqueduct produces upstream ventricular enlargement, raised intracranial pressure and potentially rapid neurological deterioration.
2
Cerebellar network injury
Vermian or hemispheric disease disrupts axial balance, timing, coordination and calibration of voluntary movement across several functional tasks.
3
Brainstem compression
Compact cranial-nerve nuclei, long tracts and cardiorespiratory centres can be affected together, creating disproportionate neurological and physiological risk.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Hydrocephalus and pressureRed flag

Ask about progressive headache, repeated vomiting, drowsiness, transient visual obscurations and diplopia; examine consciousness, pupils, fundi and upgaze. Rapid change requires emergency imaging even if headache is not dramatic.

Midline cerebellar syndrome

Truncal instability, broad-based gait and inability to sit or stand unsupported suggest vermis involvement. In children, regression of walking or reluctance to mobilise may be the clearest clue.

Cerebellar hemisphere syndrome

Look for ipsilateral dysmetria, intention tremor, dysdiadochokinesia, rebound and scanning dysarthria. Weakness alone is not the defining deficit, although long-tract compression can coexist.

Brainstem and cranial nervesRed flag

Assess eye movements, facial sensation and movement, hearing, palate, voice, tongue, swallowing and limb reflexes. Multiple cranial neuropathies with long-tract signs indicate a compact brainstem process.

Childhood presentation

Use collateral history for morning vomiting, irritability, developmental regression, falls, school change and head tilt. A child’s examination and tumour spectrum differ from those of adults and need a paediatric pathway.

Adult pattern

Review known cancer, hearing trajectory, von Hippel–Lindau features and extra-axial imaging clues, while keeping metastasis, schwannoma, meningioma, haemangioblastoma and primary glial disease open until specialist review.

Red flags requiring action

Declining consciousness, abnormal pupils, respiratory irregularity or rapidly progressive weakness with a posterior-fossa lesion indicates a pressure emergency.
Repeated or early-morning vomiting, worsening headache, papilloedema or impaired upgaze can reflect obstructive hydrocephalus rather than a primary gastrointestinal disorder.
New truncal or gait ataxia, dysmetria, nystagmus, dysarthria or cranial-nerve palsy localises to cerebellar or brainstem networks and requires timely imaging.
A child with newly abnormal cerebellar or other central neurological function follows a very urgent paediatric assessment pathway; adult tumour epidemiology and treatment must not be copied across.
Sudden severe headache or abrupt deficit raises haemorrhage, infarction or acute CSF obstruction in addition to tumour progression.
Neck stiffness with headache and vomiting can occur with posterior-fossa pathology but also infection or subarachnoid haemorrhage; lumbar puncture is unsafe until mass effect has been assessed.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Serial neurological and brainstem examinationFirst step
Why
Track consciousness, pupils, ocular movements, lower cranial nerves, long-tract signs, limb coordination, sitting and gait.
Interpretation and limitations
Trend matters more than a single score. New drowsiness, pupil change, dysphagia or respiratory abnormality signifies deterioration even if limb power remains preserved.
02
Urgent non-contrast CT head
Why
Rapidly detect hydrocephalus, haemorrhage, fourth-ventricle effacement and major posterior-fossa mass effect in an acutely deteriorating patient.
Interpretation and limitations
CT is fast but suffers bone artefact and can miss small or infiltrative posterior-fossa lesions. A negative CT does not end assessment when neurological findings persist; MRI is needed when safe.
03
Contrast-enhanced MRI brain
Why
Define tumour compartment, relation to fourth ventricle, brainstem, cranial nerves and vessels, and features guiding safe biopsy or resection.
Interpretation and limitations
Diffusion, enhancement, perfusion and spectroscopy may narrow the differential but do not substitute for integrated pathology. Surgical planning must account for eloquent adherence rather than pursue radiological completeness at any cost.
04
MRI spine for entity-specific neuraxis staging
Why
Detect CSF dissemination when medulloblastoma, ependymoma or another seeding-prone tumour is suspected.
Interpretation and limitations
NCI PDQ supports whole brain and spine assessment in childhood ependymoma and neuraxis staging in medulloblastoma. This is not a blanket requirement for every adult posterior-fossa lesion.
05
Histology and molecular classification
Why
Establish the current tumour entity and risk features needed for prognosis and adjuvant treatment.
Interpretation and limitations
Location-based labels such as “posterior-fossa tumour” are incomplete. Molecular subgrouping is central in medulloblastoma and ependymoma and paediatric-type gliomas differ biologically from adult tumours.
06
Baseline hearing, vision, swallowing and endocrine assessment
Why
Document functions vulnerable to tumour and treatment and guide rehabilitation and surveillance.
Interpretation and limitations
The selected assessments depend on anatomy and proposed therapy. Cranial irradiation and some systemic treatments create long-term hearing, endocrine and neurocognitive risks in children.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Posterior-circulation stroke

Abrupt vertigo, ataxia or cranial neuropathy demands a stroke pathway; tumour usually evolves more progressively but can bleed.

Inflammation or demyelination

Brainstem and cerebellar inflammatory lesions may enhance and mimic tumour, requiring clinical, imaging and sometimes tissue correlation.

Abscess

Fever may be absent; diffusion, infection source and systemic context guide urgent antimicrobial and surgical assessment.

Vestibular disorder

Peripheral vertigo usually lacks long-tract signs, severe truncal ataxia and multiple cranial neuropathies found in central posterior-fossa disease.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Emergency pathwayPosterior-fossa mass with acute hydrocephalusFirst stepA child or adult with ataxia and vomiting becomes drowsy and imaging shows ventricular enlargement above a fourth-ventricle mass.

1Call the age-appropriate neurosurgical, anaesthetic and critical-care teams, stabilise airway and circulation, repeat consciousness, pupils and brainstem observations, and avoid lumbar puncture.
2DefinitiveObtain immediate CT if not already performed and proceed to specialist MRI only when physiologically safe; neurosurgery decides whether urgent CSF diversion, tumour decompression or both are required. This shared anatomical emergency response does not erase the need for age- and entity-specific definitive oncological treatment.
3After pressure is controlled, complete contrast MRI and plan maximal safe tissue diagnosis or resection with neuro-oncology, balancing tumour control against brainstem and cranial-nerve injury.
4Use current integrated pathology and age-specific staging to select adjuvant therapy; do not apply an adult metastasis or glioma regimen to a child.
5Monitor hydrocephalus, cranial nerves, swallowing, gait and treatment effects, with paediatric rehabilitation and late-effects planning when applicable.

02Paediatric tumour pathwayStable child with a posterior-fossa massMRI shows a cerebellar or fourth-ventricle tumour without current cardiorespiratory deterioration.

1Refer to a paediatric neuroscience and neuro-oncology centre, document hydrocephalus and neurological baseline, and review the imaging before any procedure.
2Obtain maximal safe tissue diagnosis or resection; operative ambition is constrained by brainstem, peduncle, lower cranial-nerve and fourth-ventricle-floor relationships.
3Classify the tumour molecularly and complete neuraxis staging when the entity warrants it, then use age- and risk-adapted therapy rather than a generic posterior-fossa protocol.
4Plan rehabilitation, hearing, endocrine, growth and neurocognitive surveillance from diagnosis because late effects can be treatment-defining.

03Adult tumour pathwayStable adult posterior-fossa lesionAn adult has progressive unilateral limb ataxia and a contrast-enhancing cerebellar lesion without acute hydrocephalus.

1Characterise neurological function, cancer history and systemic fitness and obtain complete contrast MRI.
2Discuss through the adult neuro-oncology MDT whether systemic staging, resection, biopsy or surveillance best establishes diagnosis and preserves function.
3Select surgery, radiotherapy, systemic treatment or supportive care from the final entity, anatomy, extracranial disease, performance and patient priorities.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Acute hydrocephalus

Rapid ventricular enlargement can cause drowsiness, cardiorespiratory compromise and herniation and may need immediate specialist CSF diversion.

Bulbar dysfunction

Lower cranial-nerve injury causes aspiration, weak cough, impaired airway protection and substantial nutritional and respiratory compromise.

Posterior-fossa syndrome

Children can develop postoperative mutism or affective, behavioural and cognitive disturbance after cerebellar surgery, requiring specialist rehabilitation.

Long-term treatment effects

Radiotherapy and systemic therapy can affect cognition, hearing, endocrine function, growth, vascular health and secondary-tumour risk over years.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat consciousness, pupils, ocular movements, swallowing, limb coordination and gait whenever symptoms change; posterior-fossa deterioration can be abrupt.
Track ventricular size and clinical hydrocephalus after diversion or resection rather than assuming tumour treatment has permanently restored CSF flow.
Use entity- and age-specific MRI surveillance, including neuraxis imaging only when indicated by tumour biology or symptoms.
Assess hearing, endocrine, growth, cognition, education and psychosocial function during paediatric survivorship, especially after craniospinal or posterior-fossa therapy.
Reassess swallowing, aspiration risk, cranial neuropathies and mobility early so rehabilitation and nutritional support are not postponed until oncological treatment ends.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Vomiting can localise

Persistent vomiting plus gait change or cranial-nerve findings may reflect fourth-ventricle obstruction even without a focal limb weakness.

CT has a blind spot

Posterior-fossa beam-hardening artefact reduces CT sensitivity. CT is excellent for rapid hydrocephalus triage, but persistent localising findings require MRI.

Diversion is not diagnosis

Relieving hydrocephalus treats pressure but neither identifies the tumour nor removes the long-term risk of recurrent obstruction.

Maximal means safe

A small residual adherent to the fourth-ventricle floor may be preferable to permanent lower cranial-nerve or brainstem injury.

Age changes biology

The same radiological compartment contains different molecular entities across childhood and adulthood, so treatment evidence must follow the actual population.

11Common pitfallsFrequent interpretation and management errors.

01
Calling repeated vomiting gastrointestinal when gait, eye movement or alertness is changing.
02
Performing lumbar puncture before excluding obstructive hydrocephalus and posterior-fossa mass effect.
03
Letting a negative emergency CT overrule persistent cerebellar or brainstem signs.
04
Assuming all childhood posterior-fossa tumours are medulloblastoma or all adult lesions are metastases.
05
Equating complete radiological resection with good surgery when brainstem or cranial-nerve function would be sacrificed.

Find your next topic