Cerebellum & Cerebellar Disorders
Learning objectives
- LO 1Find the cerebellum's lobes, fissures, longitudinal zones and peduncles on a specimen, and pair each of the four deep nuclei with the strip of cortex that feeds it.
- LO 2Name the three layers of cerebellar cortex and the five neuron types that live in them, including which ones excite and which inhibit.
- LO 3Sort the cerebellum's inputs by where they start (spinal cord, brainstem, cerebral cortex) and say what information each one delivers.
- LO 4List the cerebellum’s major exit routes and trace its two big circuits (the spinal loop and the cerebral loop) step by step: Purkinje cell → deep nucleus → brainstem, cord or motor-cortex target.
- LO 5Use the two midline crossings (cerebellum → thalamus → cortex, then corticospinal) to explain why cerebellar signs appear on the same side as the lesion.
- LO 6Predict what anterior-, posterior- and flocculonodular-lobe lesions look like at the bedside, and use that to localize the lesion in the "failed sobriety test" case.
MAPBig picture
- ~10% of brain volume → >50% of its neurons (mostly granule cells)
- Cortex decides what → cerebellum decides how (how far, how fast, how smooth, when to stop)
- Compares plan (cortex via pons) vs actual movement (cord, vestibular, olive) → corrects now (feedback) → predicts next time (feedforward)
- Inputs → cortex → Purkinje (−) → deep nuclei (+) → brainstem / thalamus
- Vermis → fastigial · paravermis → interposed · lateral hemisphere → dentate
- Flocculonodular lobe → vestibular nuclei
- Output crosses → descending tracts cross back → ipsilateral signs
- Lesion → no paralysis, no numbness → missed targets · sway · scanning speech (looks drunk)
LO 1Gross anatomy & deep nucleiLobes, fissures, zones, peduncles, and which strip of cortex feeds which nucleus
Q1. Where is the cerebellum, and what is it made of?
- Sits in the posterior cranial fossa, dorsal to the pons and medulla, and forms the roof (posterior wall) of the 4th ventricle.
- Like the cerebrum: outer gray matter cortex folded into thin leaves (folia, the "branches") over an inner white matter core (the "trunk"; together = arbor vitae, "tree of life").
- Buried in that white matter: the deep cerebellar nuclei, just above the roof of the 4th ventricle.
- Attached to the brainstem by three pairs of peduncles (superior, middle, inferior).
CheckWhy might a swollen cerebellum (hemorrhage, big tumor) cause hydrocephalus?
Q2. How is it divided into lobes (the transverse cuts)?
| Lobe | Boundary | Body map / role |
|---|---|---|
| Anterior | Above the primary fissure | Trunk + proximal limbs → posture, gait, tone |
| Posterior | Between primary and posterolateral fissures (largest lobe) | Bigger map of distal limbs → fine, skilled coordination; also cognition |
| Flocculonodular | Below the posterolateral fissure: nodulus (midline) + 2 flocculi | Balance + eye movements (vestibular) |
- Anterior + posterior = corpus cerebelli.
- Horizontal fissure: within the posterior lobe, separates superior from inferior surface.
- Tonsils: inferior, medial parts of the posterior lobe, right above the foramen magnum.
CheckWhich fissure isolates the "balance" part of the cerebellum, and which part of it lies in the midline?
Q3. How is it divided from medial to lateral (the longitudinal strips), and which deep nucleus serves each strip?
This is the organizing principle of the whole topic: medial cortex → medial nucleus → medial (axial) motor systems; lateral cortex → lateral nucleus → limb and planning systems.
| Cortical zone | Functional division | Deep nucleus | Controls |
|---|---|---|---|
| Lateral hemisphere | Cerebrocerebellum | Dentate | Planning, timing, sequencing of skilled distal movement; cognition |
| Paravermis (intermediate) | Spinocerebellum | Interposed (emboliform + globose) | Ongoing execution of distal limb movement |
| Vermis | Spinocerebellum | Fastigial | Axial/proximal muscles: posture, gait, tone |
| Flocculonodular lobe | Vestibulocerebellum | Vestibular nuclei | Balance, eye movements (VOR, gaze holding) |
- All four deep nuclei sit in the white matter; dentate = largest, most lateral.
- The deep nuclei are the only true efferent pathway out of the cerebellum (flocculonodular Purkinje cells reach the vestibular nuclei directly) → lesion them and the cortex cannot "talk" to the rest of the brain.
CheckPurkinje cells in the paravermis are damaged. Which deep nucleus loses its inhibitory input?
Memory tool — deep nuclei
"Don't Eat Greasy Food" = Dentate, Emboliform, Globose, Fastigial, from lateral → medial. Fastigial is closest to the Fourth ventricle roof (midline). E + G = "interposed" because they are placed between dentate and fastigial.
Step 1 trap
The dentate nucleus (cerebellum) and the inferior olivary nucleus (medulla) both look like a crumpled, wavy bag of gray matter on sections. Check the location: olive = ventral medulla beside the pyramid; dentate = cerebellar white matter.
Q4. What are the three peduncles, and which way does traffic flow in each?
| Peduncle | Connects to | Direction | Main fibers |
|---|---|---|---|
| Superior (SCP) brachium conjunctivum | Midbrain | Mainly OUT | Dentate + interposed → red nucleus and VL/VA thalamus (crossing in the caudal midbrain). Input exception: ventral spinocerebellar tract. |
| Middle (MCP) brachium pontis | Pons | IN only (largest) | Pontocerebellar fibers from the contralateral pontine nuclei (relaying cerebral cortex) |
| Inferior (ICP) restiform body | Medulla | Mostly IN | Dorsal spinocerebellar, cuneocerebellar, olivocerebellar (climbing fibers), vestibular, reticular. Out: cerebellum → vestibular nuclei and reticular formation (fastigial + flocculonodular) |
CheckAn MS plaque sits only in the left MCP. Which information can no longer reach the left cerebellar hemisphere?
Step 1 HY — peduncles
- SCP = main output (S = "Sends"). MCP = pontine input (largest). ICP = cord, olive and vestibular input.
- Inputs reach the cerebellum by MCP + ICP; outputs leave by SCP (and ICP for vestibular/reticular targets).
Memory tool — peduncles
SCP = Sends out. MCP = from the Metencephalon (pons), the cortex's "mail slot". ICP = Input from the cord, olive and inner ear.
Buzzwords
ApplyLO 1 application questions
A1A neurosurgeon reports a tumor "arising from the nodulus." Which functional division and deep-nucleus equivalent are involved, and what signs do you expect?
A2A lesion confined to the most medial deep nucleus would mostly affect which muscles?
A3On a horizontal section you see a large, wavy gray band lateral in the cerebellar white matter. Name it and its cortical input.
A4Why can a small stroke cause only truncal signs, or only nystagmus, or only one-limb dysmetria?
LO 2Cerebellar cortex: layers & neuronsThree layers, five cell types, one output
Q1. What are the three layers of cerebellar cortex?
| Layer (surface → deep) | Contents |
|---|---|
| 1. Molecular | Stellate (−) and basket (−) cells; Purkinje dendrites; parallel fibers. Few cells → pale pink. |
| 2. Purkinje | One row of large Purkinje cell bodies (−) |
| 3. Granular | Huge numbers of granule cells (+) and Golgi cells (−); mossy fibers end here. Dark blue (tiny nuclei). |
Below the granular layer is white matter, then the deep nuclei.
CheckWhich layer would you see as a dense sea of tiny dark nuclei on H&E?
Memory tool — layers
Surface to depth: "MPG" — Molecular, Purkinje, Granular (like miles per gallon). Neurons by layer: "Stella and her Basket in the Molecule; Golgi and the Granules down below."
Q2. What are the five neurons, and which ones excite?
| Neuron | Layer | Sign | Job |
|---|---|---|---|
| Granule cell | Granular | + (glutamate) | Receives mossy fibers; axon rises and splits into parallel fibers that cross many Purkinje dendrites. The only excitatory neuron of the cerebellar cortex. |
| Golgi cell | Granular | − | Inhibits granule cells (gain control of mossy input) |
| Purkinje cell | Purkinje | − (GABA) | Integrates everything; the only neuron that projects out of the cerebellar cortex → deep nuclei (and vestibular nuclei). Largest neurons in the CNS. |
| Stellate cell | Molecular | − | Inhibits Purkinje dendrites |
| Basket cell | Molecular | − | Wraps and inhibits Purkinje cell bodies (lateral inhibition, sharpens the signal) |
CheckOf the five cortical neuron types, how many are inhibitory?
Q3. How is the circuit wired, from input to output?
CheckIf Purkinje cells degenerate, does deep-nucleus firing go up or down? What happens to movement?
Step 1 HY
- Purkinje cells: GABAergic, inhibitory, sole output of the cerebellar cortex, target the deep nuclei (and vestibular nuclei).
- Deep nuclei: excitatory output to the brainstem and thalamus.
- Alcohol potentiates GABA-A transmission and hits the cerebellum first → ataxia, slurred speech, dysmetria, nystagmus (the roadside sobriety test is a cerebellar exam). Chronic use → anterior vermis degeneration (wide-based gait, arms relatively spared).
Step 1 trap
Mossy fibers do NOT synapse on Purkinje cells. They synapse on granule cells, whose parallel fibers then contact Purkinje dendrites. Only climbing fibers synapse directly on Purkinje cells. Also: the Purkinje cell is inhibitory, but the cerebellum's final output (deep nuclei) is excitatory.
Buzzwords
Image drill · Michigan SecondLook
1 · Name the arrowed cell, its transmitter and its target. (tap for answer)
It is the only output of the cerebellar cortex and it is GABAergic (inhibitory).
ApplyLO 2 application questions
A1A drug selectively blocks GABA-A receptors on deep-nucleus neurons. Which synapse is affected?
A2After several drinks, a man has a wide-based gait, slurred speech and misses his nose. Explain at the synaptic level.
A3A pathologist sees loss of the large neurons forming a single row between the pale and the dark layers. Which cells, and what is lost functionally?
LO 3Afferents: what goes inSpinal cord, brainstem and cerebral cortex inputs, and what each carries
Q1. What information does the cerebellum need, and why?
Its job is to blend the cortical plan with constantly changing information and execute it fast. To compare plan vs reality it needs:
Interoceptive (inside the body)
- Body position (non-conscious proprioception: spindles, GTOs)
- Head position (vestibular)
- Muscle tone
Exteroceptive (outside world)
- Vision
- Hearing
- Touch
Plus the plan itself from the cerebral cortex. The cerebellum's own functions: timing of movement, maintaining posture/position in space, maintaining muscle tone, and timing and sequencing of language, attention and working memory.
CheckReaching for a cup requires five things. Name them.
Q2. Mossy fibers vs climbing fibers: what is the difference?
| Mossy fibers | Climbing fibers | |
|---|---|---|
| Source | Every input except the inferior olive: pontine nuclei, spinal cord, vestibular nuclei, reticular formation | Inferior olivary nucleus only |
| Peduncle | MCP (pontine), ICP (spinal, vestibular), SCP (ventral spinocerebellar) | ICP (olivocerebellar) |
| Ends on | Granule cells in the granular layer (→ parallel fibers → many Purkinje cells) | Climb to the molecular layer and wrap the dendrites of one Purkinje cell (1:1) |
| Transmitter | Excitatory, glutamate | Excitatory, aspartate |
| Collaterals | Both send excitatory collaterals directly to the deep nuclei | |
| Meaning | Ongoing context (where everything is now) | Error / teaching signal for motor learning |
CheckA tracer injected into the pontine nuclei labels terminals in which cerebellar layer?
Memory tool
Climbing fibers climb from the Olive ("a vine climbing an olive tree") and grip one Purkinje cell like a vine on one trunk. Mossy fibers are the moss covering everything else.
Step 1 trap
Olivocerebellar (climbing) fibers enter through the inferior cerebellar peduncle, not the middle one. Only pontocerebellar fibers use the MCP.
Q3. Which pathways bring information in, and what does each carry?
| Source | Pathway | Information | Destination |
|---|---|---|---|
| Spinal cord | Dorsal (posterior) spinocerebellar | Position and tone of individual muscles of the legs / lower body | Spinocerebellum (ICP) |
| Ventral (anterior) spinocerebellar | Muscle groups of the legs / lower body (whole-limb activity) | Spinocerebellum (SCP) | |
| Cuneocerebellar | Muscles of the arms / upper body | Spinocerebellum (ICP) | |
| Brainstem | Olivocerebellar | Flexor-reflex afferents relayed via the inferior olive (climbing fibers) | Vermal + paravermal areas |
| Reticulocerebellar | Muscle tone, posture and balance | Vermal + paravermal areas | |
| Vestibulocerebellar | Head position, posture and balance | Vestibulocerebellum + paravermal areas | |
| Cerebral cortex | Corticopontine → pontocerebellar | Motor plan (motor/premotor, plus prefrontal/parietal) | Contralateral lateral hemisphere (MCP) |
CheckWhich spinal pathway carries upper-limb proprioception to the cerebellum, and what is its relay nucleus?
Step 1 HY
- Cortex reaches the cerebellum only through relays: cortex → ipsilateral pontine nuclei → cross → contralateral MCP. There is no direct cortex–cerebellum connection.
- Spinocerebellar tracts carry non-conscious proprioception (no thalamic relay, no awareness). Conscious proprioception travels in the dorsal columns (DCML).
- Friedreich ataxia damages spinocerebellar tracts and dorsal columns, so ataxia comes with a positive Romberg.
Buzzwords
ApplyLO 3 application questions
A1Damage to the right inferior olive would remove climbing-fiber input from which side of the cerebellum?
A2A patient loses vibration and position sense in the legs and sways only when he closes his eyes. Is this a cerebellar input problem?
A3Predict the main effect of losing all mossy-fiber input but keeping climbing fibers.
LO 4Efferents & the two loopsFrom deep nucleus to cord, brainstem and motor cortex
Q1. What are the major efferent tracts?
| Tract | From → to | Purpose |
|---|---|---|
| Dentatorubrothalamic | Dentate → SCP (crosses) → red nucleus and VL/VA thalamus → motor/premotor cortex | Planning and coordination of voluntary movement |
| Cerebello-olivary | Cerebellum (deep nuclei) → inferior olive | Closes the learning loop (olive sends climbing fibers back) |
| Cerebellovestibular | Flocculonodular lobe (and fastigial) → vestibular nuclei (via ICP) | Balance, axial posture, eye movements |
Overall purpose of the efferents: coordination, planning and execution of movement.
Q2. Where does the cerebellum sit in the motor hierarchy?
- Cerebrocerebellum = planning (before the movement). Spinocerebellum = execution + feedback (during the movement).
- The cerebellum talks directly only to the brainstem and thalamus; it influences cortex and cord through them.
Q3. Trace the cerebrocerebellar and spinocerebellar loops.
Cerebrocerebellum (lateral hemisphere → dentate)
- In: motor/premotor cortex → pontine nuclei → contralateral MCP → lateral hemisphere. Extra input from the inferior olive (ICP).
- Out: dentate → SCP → crosses in the midbrain →
- Reticular formation: tone and coordination
- Red nucleus: motor refinement
- VL thalamus → motor/premotor cortex (area 6)
- Inferior olive: feedback loop for motor learning
- Role: planning, programming and timing of complex skilled movement (e.g., feeling around for an object you cannot see); motor learning.
- Dorsal dentate → primary motor + premotor cortex (motor). Ventral dentate → prefrontal + posterior parietal cortex (non-motor/cognitive).
Spinocerebellum (vermis + paravermis)
- In: spinocerebellar tracts (plus trigeminal; vermis also gets visual, auditory, vestibular input).
- Vermis → fastigial → vestibular nuclei + reticular formation (vestibulospinal, reticulospinal = medial systems), also VA/VL → trunk motor cortex, and inferior olive → axial/proximal muscles, posture, balance.
- Paravermis → interposed → SCP → contralateral red nucleus (rubrospinal = lateral system) and VA/VL → distal limb coordination.
- Role: modulates ongoing movement using proprioceptive feedback.
Vestibulocerebellum (flocculonodular lobe ↔ vestibular nuclei, all via ICP)
- Descending: modulates the vestibulospinal tract → axial/proximal muscles, posture, balance.
- Ascending: modulates vestibulo-ocular pathways via the MLF to CN III, IV, VI → eye movements.
- Lesion → nystagmus, truncal ataxia, postural instability.
- Feedback control: compares planned vs executed movement → can only correct using recent past activity
- Motor: overshoot when reaching
- Cognitive: perseverating on a topic
- Feedforward control: uses past experience to predict (associative learning)
- Other people's motion: walking through a crowd
- Speech: anticipating a punchline
CheckMatch each task to a division: (1) keeping your balance on a rocking boat, (2) a pianist planning a fast run, (3) adjusting your stride on uneven ground.
Step 1 HY
- Output pathway to cortex: deep nuclei → SCP → (decussation) → contralateral VL thalamus → motor cortex.
- Medial = axial (fastigial, vestibulospinal/reticulospinal), lateral = limb (interposed → rubrospinal; dentate → thalamus → corticospinal).
- Deep brain stimulation for disabling cerebellar/essential tremor targets the VL (Vim) thalamus, the relay for dentatothalamic fibers, not the cerebellar nuclei.
Step 1 trap
"The cerebellum projects to motor cortex" is true only via the thalamus. If an answer choice offers a direct cerebellum → cortex projection, or says the cerebellum projects directly to spinal motor neurons, it is wrong. Its influence on the cord is always through brainstem tracts or cortex.
Memory tool
Think of the cerebellum as a sports coach: the cerebrocerebellum draws up the play before the snap, the spinocerebellum shouts corrections during the play, and the vestibulocerebellum keeps the players on their feet. The inferior olive is the video review that teaches next time.
ApplyLO 4 application questions
A1A patient with a disabling cerebellar intention tremor improves after deep brain stimulation. Where was the electrode most likely placed?
A2Why do cerebellar patients overshoot a target, then correct back and forth?
A3A lesion of the SCP just before its decussation would interrupt output from which nuclei?
A4A patient with a posterior-lobe lesion names only 6 animals in 60 seconds and has trouble with planning. Which output channel explains this?
LO 5Why cerebellar signs are ipsilateralTwo crossings cancel out
Q1. Where are the two crossings?
The inputs obey the same rule: spinal tracts describing the right body reach the right cerebellum (dorsal spinocerebellar/cuneocerebellar stay ipsilateral; ventral spinocerebellar crosses twice), and the left cortex talks to the right cerebellum through the crossed pontocerebellar fibers. So: right cerebellum = right body.
CheckA left cerebellar hemisphere stroke. Which arm shows the intention tremor, and which motor cortex is "receiving bad timing"?
Step 1 HY — laterality
- Cerebellar hemisphere lesion → ipsilateral limb ataxia; patient falls/veers toward the side of the lesion.
- Cerebral cortex lesion → contralateral weakness. Cerebellar lesion → ipsilateral incoordination without true weakness.
- Midline (vermis) lesion → bilateral, mostly truncal signs.
Step 1 trap
A lesion of the SCP after its decussation (or of the VL thalamus / red nucleus) gives contralateral ataxia relative to that lesion, because you are past the first crossing. Likewise, a lesion of the pons/MCP causes ataxia ipsilateral to the MCP, but the pontine nuclei themselves relay the contralateral cortex. Always ask: "which side of which crossing?"
Memory tool
"Two wrongs make a right": two crossings → the right cerebellum runs the right side. Or: the cerebellum is the "same-side syndrome."
Image drill · Michigan SecondLook
1 · Find the lesion. Which side will the ataxia be on? (tap for answer)
Expect LEFT-sided (ipsilateral) limb ataxia, dysmetria, dysdiadochokinesia and intention tremor.
Secondary prevention: aspirin + risk-factor control (HTN, diabetes, lipids, smoking, alcohol).
ApplyLO 5 application questions
A1A lacunar infarct destroys the left VL thalamus. On which side would cerebellar-type incoordination appear, if any?
A2A patient veers to the left when walking and has dysmetria of the left arm and leg. Where is the lesion?
A3A midline vermis tumor: unilateral or bilateral signs?
LO 6Lesions, syndromes & the casePredict the deficit, localize the lesion
Q1. What are the cerebellar signs and how do you test them?
| Sign | What it looks like / test | Main structure | Division |
|---|---|---|---|
| Ataxia | Poor coordination and accuracy; unsteady, wide-based gait; can't walk heel-to-toe (tandem) | Deep nuclei / vermis (fastigial) for gait | Spinocerebellum |
| Dysmetria | Wrong range, direction or force: over/undershoots on finger-to-nose, heel-to-shin | Dentate | Cerebrocerebellum |
| Dysdiadochokinesia | Can't do rapid alternating movements (pronation/supination, hand flipping) | Dentate (+ interposed) | Cerebrocerebellum |
| Intention tremor | Absent at rest; appears with movement and worsens as the target is approached | Dentate and its outflow (SCP) | Cerebrocerebellum |
| Hypotonia | Floppy limbs, ↓ resistance to passive movement; pendular knee jerk | Cerebellar cortex or deep nuclei | Spino-/cerebrocerebellum |
| Dysarthria | Scanning / staccato speech: irregular rhythm, syllables chopped and evenly stressed | Lateral hemispheres | Cerebrocerebellum |
| Nystagmus | Rhythmic eye oscillation (gaze-evoked, worse looking toward the lesion), vertigo, imbalance | Flocculonodular lobe | Vestibulocerebellum |
| Rebound | Arm flies back when the examiner suddenly releases resistance (failure to "check") | Hemisphere | Spino-/cerebrocerebellum |
CheckHow do you tell cerebellar intention tremor from Parkinson tremor at the bedside?
Memory tool — DANISH
Dysdiadochokinesia, Ataxia, Nystagmus, Intention tremor, Scanning (slurred) speech, Hypotonia (and heel-to-shin / finger-to-nose dysmetria).
Step 1 HY — Romberg
- Romberg sign tests conscious proprioception (dorsal columns): stable with eyes open, falls with eyes closed = positive.
- Cerebellar ataxia is unsteady even with eyes open and is not dramatically worsened by eye closure, so Romberg is classically negative (or cannot be done). Vision cannot replace a cerebellum.
- Positive Romberg + ataxia: B12 deficiency, tabes dorsalis, Friedreich ataxia, sensory neuropathy.
Step 1 trap
Dysdiadochokinesia + ataxia → think cerebellum, not basal ganglia. Basal ganglia disease gives resting tremor, rigidity, bradykinesia or involuntary movements (chorea, hemiballismus), not dysmetria. Cerebellar patients have normal strength, sensation and reflexes (reflexes may be pendular, never hyperreflexic).
Q2. What do anterior, posterior and flocculonodular lobe lesions look like?
Anterior lobe syndrome spinocerebellum
Lower-limb and gait ataxia ("walks as though drunk"), truncal ataxia from vermis involvement (unsteady even when the trunk is supported), only slight upper-limb ataxia. Classic cause: chronic alcohol (anterior-superior vermis).
Posterior lobe syndrome usually ipsilateral
Ataxia of both arm and leg on one side (pulled to that side "as if by a magnet" when walking). If the dentate is involved: dysmetria, dysdiadochokinesia, intention tremor, scanning speech. Plus the cerebellar cognitive affective syndrome.
Flocculonodular syndrome vestibulocerebellum
Disturbed balance: loss of equilibrium, tendency to fall over, nystagmus / eye-movement problems. Limb coordination is spared (no dysmetria lying down).
CheckWhat is the cerebellar cognitive affective syndrome?
Step 1 trap
Some summaries say "anterior lobe = upper limb." Go with the body map: the anterior lobe represents the trunk and proximal limbs (posture, gait), and anterior lobe syndrome is leg/gait + truncal ataxia with only slight arm involvement.
Buzzwords
Q3. The case: a "drunk driver" with zero blood alcohol. Where is the lesion?
Case
A 35-year-old woman is stopped on suspicion of drunk driving: slurred speech, imbalance even with eyes open, can't walk heel-to-toe or stand on one leg, nystagmus on lateral gaze, worst looking right, repeatedly misses her nose with the right hand. Blood alcohol 0, drug screen negative. The neurologist adds: onset over 2 weeks; right dysmetria and intention tremor; right dysdiadochokinesia; staccato speech; low verbal fluency (6 animals in 60 s); normal strength, sensation, reflexes.
| Finding | Points to |
|---|---|
| Imbalance with eyes open, can't tandem walk or stand on one leg | Vermis/paravermis (spinocerebellum); not a Romberg (sensory) problem |
| Right dysmetria, intention tremor, dysdiadochokinesia | Right lateral hemisphere + dentate (ipsilateral rule) |
| Staccato / slurred speech | Lateral hemispheres |
| Low verbal fluency | Posterior lobe → cognitive affective syndrome |
| Nystagmus, worse looking right | Flocculonodular component; gaze-evoked nystagmus is worse toward the lesion side |
| Normal strength, sensation, reflexes | Pure cerebellar: CST, DCML and spinothalamic spared |
| Subacute onset over 2 weeks, young woman | Inflammatory demyelination (MS) rather than stroke (sudden) or degeneration (years) |
Localization: a right posterior-lobe lesion (vermis/paravermis + lateral hemisphere with the dentate), plus a flocculonodular component.
Diagnosis: multiple sclerosis: demyelinating plaque in the right cerebellar hemisphere centered on the dentate, extending into the right MCP and right side of the brainstem.
CheckWhy are all of her limb signs on the right, if the plaque is in the right cerebellum?
Step 1 HY — MS
MS loves the cerebellum, its peduncles and the brainstem. Charcot triad: Scanning speech, Intention tremor, Nystagmus ("SIN"). Also look for optic neuritis, INO (MLF), periventricular plaques (Dawson fingers), oligoclonal bands in CSF.
Q4. Which cerebellar diseases does Step 1 love?
Alcoholic cerebellar degeneration
Anterior-superior vermis atrophy → wide-based gait and truncal ataxia, legs > arms. Acute intoxication: GABA-A potentiation → all cerebellar signs. Look for Wernicke (thiamine: ataxia + ophthalmoplegia + confusion).
Friedreich ataxia
AR GAA repeat, frataxin (chr 9), mitochondrial iron. Spinocerebellar tracts + dorsal columns + lateral CST + DRG: ataxia with positive Romberg, ↓ reflexes but Babinski +, pes cavus, kyphoscoliosis, hypertrophic cardiomyopathy (cause of death), diabetes. Teens.
Spinocerebellar ataxias (SCA)
AD CAG (polyglutamine) repeats with anticipation; progressive adult-onset gait ataxia, dysarthria, nystagmus; Purkinje cell loss.
Ataxia-telangiectasia
AR ATM (DNA double-strand break repair). Childhood cerebellar ataxia (Purkinje loss), oculocutaneous telangiectasias, IgA deficiency → sinopulmonary infections, ↑ AFP, ↑ lymphoma/leukemia, radiation sensitivity.
Medulloblastoma
Most common malignant pediatric brain tumor; vermis / 4th ventricle roof. Truncal ataxia, nystagmus, obstructive hydrocephalus (morning headache, vomiting, papilledema), drop metastases. Small round blue cells, Homer-Wright rosettes, synaptophysin +.
Other posterior fossa tumors
Pilocytic astrocytoma: child, cystic + mural nodule in a hemisphere, Rosenthal fibers, GFAP + (ipsilateral limb ataxia). Ependymoma: 4th ventricle, perivascular pseudorosettes. Hemangioblastoma: adult, VHL, EPO → polycythemia.
Cerebellar strokes
PICA: lateral medullary (Wallenberg) + inferior cerebellum → vertigo, nystagmus, ipsilateral limb ataxia, dysphagia/hoarseness, ipsilateral face + contralateral body pain/temp loss, Horner. AICA: lateral pons → same + facial paralysis, deafness. SCA artery: superior cerebellum → limb/gait ataxia. Hypertensive hemorrhage (Charcot-Bouchard) can compress the 4th ventricle: surgical emergency.
Chiari & Dandy-Walker
Chiari I: tonsils herniate >3-5 mm through foramen magnum; occipital headache, cerebellar signs, syringomyelia (cape-like pain/temp loss). Chiari II: vermis + tonsils, with lumbosacral myelomeningocele, hydrocephalus. Dandy-Walker: vermis agenesis, cystic 4th ventricle, enlarged posterior fossa.
Toxic / paraneoplastic
Phenytoin, carbamazepine, lithium toxicity → nystagmus, ataxia. Paraneoplastic cerebellar degeneration: anti-Yo (ovarian/breast cancer, anti-Purkinje), anti-Hu/anti-P/Q (small cell lung). Hypothyroidism and B12 deficiency also cause ataxia.
Step 1 HY — tonsillar herniation
Raised posterior-fossa pressure pushes the cerebellar tonsils through the foramen magnum → compress the medulla → cardiorespiratory arrest. Same structure that sags in Chiari I.
Step 1 trap
Child + posterior fossa mass: midline vermis, solid, drop mets → medulloblastoma; lateral hemisphere, cystic with mural nodule, good prognosis → pilocytic astrocytoma. Truncal vs limb signs tell you which.
Memory tool
Friedreich is "Fried" everywhere: fried tracts (spinocerebellar, dorsal columns, CST), fried heart (HCM), fried pancreas (diabetes), and a fried-out foot (pes cavus). GAA = "GAAit" problems.
ApplyLO 6 application questions
A1A 55-year-old man with long-standing alcohol use has a broad-based, unsteady gait and heel-to-shin ataxia, but finger-to-nose is nearly normal. Localize.
A2A 6-year-old has morning headaches, vomiting, and can't sit without swaying; nystagmus is present; finger-to-nose in bed is normal. Localize and name the likely tumor.
A3Left dysdiadochokinesia and dysmetria, gait drifting left, no nystagmus, normal equilibrium when standing still. Localize.
A4A 47-year-old with poorly controlled hypertension suddenly develops vertigo, vomiting, inability to walk and right-sided intention tremor, then becomes drowsy. Diagnosis and danger?
A5A teenager has progressive ataxia, absent ankle reflexes, upgoing toes, loss of vibration sense and an abnormal ECG. Why is his Romberg positive when most cerebellar patients' is not?
MCQPractice questionsClick an answer to see the explanation.
1A 68-year-old man has sudden vertigo and clumsiness. Exam shows past-pointing on finger-to-nose and an action tremor that worsens near the target, both in the right arm. Strength, sensation and reflexes are normal. MRI shows a small infarct. Where is it?
2A researcher labels axons that enter the cerebellum via the inferior cerebellar peduncle, ascend through the granular and Purkinje layers, and wrap around the dendritic tree of a single Purkinje cell. Where are the cell bodies of these axons?
3A 58-year-old man with 30 years of heavy drinking has a slowly progressive, wide-based, staggering gait and cannot walk heel-to-toe. Heel-to-shin testing is abnormal bilaterally; finger-to-nose is nearly normal. Eye movements and speech are normal. Which region is most affected?
4A 5-year-old boy has 3 weeks of morning headaches and vomiting. He sways when sitting unsupported and has horizontal nystagmus; limb coordination is normal when tested lying down. MRI shows a solid midline mass arising from the roof of the 4th ventricle with hydrocephalus. Biopsy would most likely show:
5A 13-year-old girl has 2 years of progressive clumsiness and falls. Exam: dysarthria, absent ankle jerks, bilateral extensor plantar responses, loss of vibration sense in the feet, positive Romberg, pes cavus and kyphoscoliosis. ECG shows left ventricular hypertrophy. The underlying defect is:
6A 50-year-old woman is unsteady with a wide-based gait. She is just as unsteady with eyes open as with eyes closed. Vibration and joint-position sense are normal in all limbs. Which statement best explains her findings?
7A demyelinating plaque is confined to the left middle cerebellar peduncle. Which fibers are interrupted?
8Purkinje cells of the lateral cerebellar hemisphere send their axons to which structure?
9Which statement about the only neuron that carries signals out of the cerebellar cortex is correct?
10A 64-year-old woman develops sudden vertigo, nausea, hoarseness and difficulty swallowing. Exam: left Horner syndrome, loss of pain and temperature on the left face and right body, nystagmus, and left arm and leg ataxia with normal strength. Occlusion of which artery?
11A 29-year-old woman with a prior episode of painful vision loss in one eye now has scanning speech, nystagmus and a coarse tremor of the right hand that worsens as she reaches for a cup. Interruption of which pathway best explains the tremor?
12A child cannot stand or walk without falling and has nystagmus, but finger-to-nose and heel-to-shin are normal while lying in bed. Purkinje cells of the damaged region project directly to which structure?
13After resection of a posterior-lobe cerebellar tumor, a 40-year-old teacher has mild limb ataxia but also struggles to plan lessons, names only a few words starting with "F" in a minute, and seems emotionally flat. Which best explains her non-motor deficits?
14A 72-year-old man has a disabling tremor of the left arm that appears when he reaches for objects and worsens near the target, due to a remote left cerebellar stroke. Medication fails. Deep brain stimulation is planned. The most appropriate target is the: