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Textbook/Clinical imaging and interpretation/Pituitary and posterior-fossa imaging
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Pituitary and posterior-fossa imaging

Choose dedicated imaging for sellar and posterior-fossa disease, recognise optic-pathway, brainstem and CSF-flow emergencies, and keep adult pituitary and age-specific posterior-fossa pathways distinct.

27 min full readUK scopeSources checked 13 Sept 2026Clinical review pending
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Small compartments can produce major emergencies

Pituitary haemorrhage can cause acute visual loss and adrenal crisis, while a posterior-fossa lesion can obstruct the fourth ventricle or compress the brainstem before a large supratentorial shift appears.

Action: Stabilise physiology, perform focused visual and neurological assessment, obtain rapid CT when necessary, and involve endocrine, neurosurgical or paediatric teams while arranging the definitive MRI protocol.

Open the sections you need. The overview is shown first.
01Purpose and principlesWhat the assessment is for and the core concepts behind it.

The sella is a small midline compartment below the optic chiasm and beside the cavernous sinuses. Coronal MRI best shows chiasmal proximity and cavernous-sinus relationships; sagittal views show stalk and suprasellar extension. T1 signal, T2 signal, diffusion and enhancement together distinguish adenoma, haemorrhage, cyst and other sellar lesions, though imaging alone rarely supplies the endocrine diagnosis.

The posterior fossa contains cerebellum, brainstem, fourth ventricle and narrow CSF pathways within rigid boundaries. CT rapidly reveals haemorrhage and hydrocephalus, but beam hardening can obscure the brainstem and cerebellum. MRI defines tissue, diffusion and cranial-nerve or foramen-magnum anatomy, although monitoring and scan duration may limit its use in unstable patients.

Age changes the differential. In children, ependymoma, medulloblastoma and low-grade glioma have different typical locations, dissemination patterns and treatment pathways. In adults, metastasis, haemangioblastoma, meningioma, schwannoma, infarction and demyelination are important. Avoid declaring histology from a single sign; describe location, CSF effect, diffusion and enhancement and refer to the specialist MDT.

Key points

  • Use a dedicated sellar MRI protocol with thin coronal and sagittal images to assess pituitary size, haemorrhage, stalk, cavernous sinuses and optic chiasm; a routine brain MRI can miss small lesions.
  • Pituitary apoplexy is treated from the clinical endocrine and visual syndrome: obtain urgent MRI when feasible, use CT as an acute alternative and never delay indicated steroid replacement for imaging.
  • Posterior-fossa interpretation follows the fourth ventricle, cerebellar hemispheres and vermis, brainstem, cisterns and foramen magnum, with special attention to CSF obstruction.
  • MRI provides superior posterior-fossa tissue contrast and diffusion, while CT is faster for acute hydrocephalus, haemorrhage and unstable patients but suffers skull-base artefact.
  • Pituitary incidentalomas need endocrine assessment and formal visual fields when the lesion abuts the optic nerves or chiasm; surveillance is lesion- and patient-specific.
  • Posterior-fossa tumour pathways differ by age and entity; neuraxis MRI may be required for dissemination, but staging must not delay treatment of acute hydrocephalus.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Sellar visual pathwayRed flag

Bitemporal field loss suggests chiasmal compression, while ophthalmoplegia may reflect cavernous-sinus involvement. Document acuity, fields and ocular movements rather than saying vision affected.

Pituitary apoplexy syndromeRed flag

Sudden headache, vomiting, reduced acuity, field loss, ocular palsy, altered consciousness and circulatory disturbance can accompany haemorrhage or infarction in a pituitary lesion.

Posterior-fossa localisationRed flag

Gait or limb ataxia, dysarthria, nystagmus, cranial-nerve deficits and long-tract signs localise to cerebellum or brainstem and can be subtle on CT.

Hydrocephalus patternRed flag

Assess fourth-ventricular distortion, enlargement upstream, transependymal CSF seepage and basal cisterns. Clinical decline converts ventricular enlargement into an emergency.

Foramen-magnum crowding

Tonsillar descent, medullary compression and a syrinx require anatomical description and symptom correlation; measurements alone do not establish causation.

Age and entity boundary

The same posterior-fossa location has different likely diagnoses and staging implications in a young child, adolescent and older adult.

Red flags requiring action

  • Sudden headache with visual loss, ophthalmoplegia, altered consciousness, hypotension or hyponatraemia suggests pituitary apoplexy and requires urgent endocrine and neurosurgical assessment.
  • Drowsiness, repeated vomiting, bradycardia, cranial-nerve dysfunction or worsening ataxia with a posterior-fossa lesion may indicate brainstem compression or obstructive hydrocephalus.
  • A child under 12 with headache plus morning waking, vomiting, ataxia, altered consciousness or squint needs same-day neurological assessment under NG127.
  • Do not perform lumbar puncture when posterior-fossa mass effect, obstructive hydrocephalus or neurological deterioration creates a herniation risk.
  • A normal or non-diagnostic CT does not exclude small sellar lesions, pituitary infarction or subtle posterior-fossa disease; persistent localising signs require MRI.
03Method and interpretationA systematic approach to the test and its findings.
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.

  1. 01
    Dedicated pituitary MRIFirst step
    Why
    Characterise sellar and suprasellar anatomy, optic-chiasm contact, cavernous-sinus involvement and haemorrhage or infarction.
    Interpretation and limitations
    Use thin coronal and sagittal pre- and post-contrast sequences with T2 and susceptibility or diffusion as indicated. Dynamic contrast is selective, not universal.
  2. 02
    Urgent non-contrast CT head
    Why
    Detect acute haemorrhage, hydrocephalus and major mass effect quickly when the patient is unstable or MRI is not immediately available.
    Interpretation and limitations
    CT may miss pituitary infarction and small posterior-fossa lesions because of limited soft-tissue contrast and skull-base artefact; a negative scan may require MRI.
  3. 03
    MRI brain with posterior-fossa sequences
    Why
    Define the lesion origin, brainstem and cerebellar involvement, diffusion, enhancement and CSF pathways.
    Interpretation and limitations
    Include thin axial sequences and contrast when tumour or inflammation is suspected. Diffusion restriction narrows but does not prove tumour type.
  4. 04
    MRI spine for neuraxis staging
    Why
    Detect leptomeningeal or drop metastases in selected posterior-fossa tumour entities.
    Interpretation and limitations
    Perform through the specialist paediatric or neuro-oncology pathway when the patient is stable; acute hydrocephalus and decompression take priority.
  5. 05
    Formal visual fields and acuity
    Why
    Quantify optic-nerve or chiasmal dysfunction and establish a baseline for intervention.
    Interpretation and limitations
    Required when a pituitary lesion abuts or compresses the optic nerves or chiasm; bedside confrontation is insufficient for stable surveillance decisions.
  6. 06
    Pituitary endocrine assessment
    Why
    Detect hormone hypersecretion and hypopituitarism, including urgent adrenal insufficiency.
    Interpretation and limitations
    Take emergency blood samples before steroids if this causes no delay, but treat suspected adrenal crisis immediately; imaging does not measure hormonal function.
04Clinical next stepsHow the result changes management or prompts escalation.
01Worked emergency pathwaySudden visual loss with a sellar lesionFirst stepAn adult presents with acute severe headache, ophthalmoplegia, visual deterioration and haemodynamic disturbance.
  1. 1Treat possible pituitary apoplexy as an endocrine emergency, obtain urgent safety and pituitary bloods if this will not delay treatment, and give indicated glucocorticoid replacement.
  2. 2Arrange urgent dedicated pituitary MRI as the investigation of choice, using CT when MRI is not immediately feasible, and contact endocrine and neurosurgical specialists.
  3. 3Use visual severity, consciousness, endocrine state and imaging to decide urgent surgery versus closely supervised conservative care.
02Stable incidental pathwayPituitary lesion found unexpectedlyA stable adult has an incidental sellar lesion and no acute apoplexy features.
  1. 1Assess hypersecretion and hypopituitarism and obtain dedicated pituitary MRI if the first imaging was not a sellar protocol.
  2. 2Arrange formal visual fields when the lesion abuts the optic nerves or chiasm.
  3. 3Set endocrine, imaging and visual surveillance from lesion size, proximity, growth and patient context rather than one universal interval.
03Paediatric posterior pathwayAtaxia with obstructive hydrocephalusA child has progressive cerebellar signs, vomiting and ventricular enlargement from a fourth-ventricular mass.
  1. 1Involve paediatric neurosurgery immediately, stabilise the pressure emergency and do not perform lumbar puncture.
  2. 2Use urgent CT to define hydrocephalus if needed, then contrast MRI brain when safe for lesion characterisation.
  3. 3Complete neuraxis staging and entity-specific MDT planning after immediate CSF-flow and brainstem threats are controlled.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
  • In suspected apoplexy, repeat visual acuity, fields, ocular movements, consciousness, blood pressure, sodium and glucose while endocrine and neurosurgical plans develop.
  • For acute posterior-fossa disease, monitor GCS, pupils, cranial nerves, gait or limb signs and vomiting; deterioration requires immediate hydrocephalus reassessment.
  • During pituitary surveillance, align MRI with endocrine and formal visual review, documenting growth in comparable planes and any new chiasmal contact.
  • After posterior-fossa treatment, track CSF diversion, neurological recovery and neuraxis findings through the entity-specific paediatric or adult MDT.
  • Ensure urgent imaging findings are directly acknowledged by the responsible specialist team and that final pathology can revise the radiological differential.
06Special situationsVariants, exceptions and circumstances that change the usual approach.

A routine brain MRI can miss

Thicker slices and non-sellar planes reduce sensitivity for small pituitary lesions; protocol selection is part of the diagnostic test.

CT is fast but limited

Its speed makes CT valuable for hydrocephalus and haemorrhage, while dense skull-base bone degrades assessment of pituitary and posterior-fossa tissue.

Chiasmal contact changes assessment

An incidental lesion abutting the optic apparatus needs formal field testing even if the patient has not volunteered visual symptoms.

Diffusion narrows a differential

Restricted diffusion can occur in hypercellular tumour, abscess and infarction; location and enhancement remain necessary for interpretation.

Staging follows stabilisation

Neuraxis imaging is important for selected childhood tumours, but a drowsy child with obstructive hydrocephalus first needs safe pressure control.

07Common pitfallsFrequent interpretation and management errors.
  1. 01

    Using a normal routine CT to exclude pituitary apoplexy or a subtle brainstem and cerebellar lesion.

  2. 02

    Waiting for MRI confirmation before treating clinically suspected adrenal crisis in pituitary apoplexy.

  3. 03

    Describing a posterior-fossa mass without its fourth-ventricular, cisternal and brainstem effects.

  4. 04

    Performing lumbar puncture for staging while acute hydrocephalus or posterior-fossa mass effect remains present.

  5. 05

    Applying adult incidentaloma surveillance intervals to a symptomatic lesion, pregnancy or a child without specialist reassessment.

Practice

Two practice questions

Question 1 of 20 correct
Clinical imaging and interpretationOriginal SBA

Imaging suspected pituitary apoplexy

An adult develops sudden severe headache, vomiting, diplopia and reduced visual acuity with hypotension and hyponatraemia. Which imaging strategy is most appropriate while emergency endocrine care proceeds?

Sources and review status6 sources · checked 13 Sept 2026 · clinical review pending
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 13 Sept 2026; clinical approval remains outstanding.

  • Society for Endocrinology emergency guidance on pituitary apoplexyPublished September 2016; presentation, differential, endocrine sampling, MRI, steroid criteria, transfer and follow-up sections read. Adult emergency guidance, not a chronic incidentaloma or paediatric protocol. Applied specifically to Pituitary and posterior-fossa imaging.
  • Endocrine Society pituitary incidentaloma guidelinePublished April 2011; baseline endocrine assessment, dedicated MRI, visual fields, surveillance and surgical-referral recommendations read from the official body. Older stable-incidentaloma guidance; intervals were not generalised to symptomatic, pregnant or paediatric patients. Applied specifically to Pituitary and posterior-fossa imaging.
  • NICE NG99 brain tumours recommendationsPublished 11 July 2018 and last updated 29 January 2021; adult structural MRI, specialist MDT and care recommendations read. Covers people over 16 and does not provide a universal posterior-fossa or pituitary-lesion algorithm. Applied specifically to Pituitary and posterior-fossa imaging.
  • NICE NG127 suspected neurological conditions in childrenPublished 1 May 2019; headache, cerebellar dysfunction and raised-pressure recognition recommendations for under-16s read, current body checked 13 September 2026. It guides referral rather than specifying tumour treatment. Applied specifically to Pituitary and posterior-fossa imaging.
  • NCI childhood ependymoma PDQ, health professional versionUpdated 6 January 2025; anatomy, clinical features, diagnostic evaluation, staging and treatment overview read. Peer-reviewed US government summary, not a formal UK guideline and not transferable to adults or other posterior-fossa histologies. Applied specifically to Pituitary and posterior-fossa imaging.
  • ENLS Intracranial Hypertension and Herniation Protocol version 6.0Updated September 2024; communication, diagnosis, Tier Zero and Tier One sections read for urgent CT and imaging-confirmed obstructive hydrocephalus. Multi-aetiology consensus, not a paediatric tumour outcomes guideline. Applied specifically to Pituitary and posterior-fossa imaging.
Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom