The putamen is the most lateral structure. The putamen is the most common site of hypertensive hemorrhage. When you can point to it on a CT, you get the question right.
Before you learn anything · take the shot:
A 48-year-old man with a long history of poorly controlled hypertension presents with sudden onset of right-sided hemiparesis and aphasia. A non-contrast CT of the head shows a hyperdense lesion in the left deep gray matter, lateral to the globus pallidus and medial to the insular cortex. Which structure is the site of hemorrhage?
That's it. Putamen · the most lateral deep gray structure, sitting right next to the insular cortex, lateral to the globus pallidus. It's fed by the lenticulostriate arteries (branches of the MCA), and those tiny arteries are the ones that blow out in chronic hypertension (Charcot-Bouchard aneurysms). Most common site of hypertensive hemorrhage. Period.
Good instinct · the caudate IS a basal ganglia structure, and bleeds there do happen. But the caudate hugs the lateral ventricle · it's way more medial. You know how a comma curls around? That's the caudate wrapping around the ventricle. "Lateral to the globus pallidus" means we're in putamen territory. Caudate = medial, wraps the ventricle. Putamen = most lateral deep gray structure.
This is the trap that got you. The globus pallidus sits MEDIAL to the putamen. The question says "lateral to the globus pallidus" · that's literally pointing at the putamen. Think of it like a sandwich: insular cortex (bread) → putamen (the meat) → globus pallidus (the other bread). The GP is deeper in. Lateral to the GP = putamen. The GP itself is more medial.
The thalamus does bleed in hypertension (second most common site), but it's even more medial · it sits next to the third ventricle, deep in the center of the brain. The question says "lateral to the globus pallidus," which puts you way more lateral than the thalamus. Think of it as: thalamus is downtown, putamen is out in the suburbs near the surface. Lateral to GP = putamen. Thalamus is medial, next to the 3rd ventricle.
Creative answer · the internal capsule IS between the putamen and caudate, and lacunar strokes there cause pure motor hemiparesis. But the internal capsule is white matter (axon tracts), not gray matter. The question specifies "deep gray matter." Also, the internal capsule is medial to the globus pallidus. Deep gray matter + lateral to GP = putamen. Internal capsule is white matter, more medial.
THE FUNCTION
What the basal ganglia actually do
Before the anatomy, the job description. The whole basal ganglia loop exists to gate movement.
Basal ganglia · job description
START, STOP, and CONTROL the movements you want. INHIBIT the movements you don't.
The basal ganglia are the brain's motor filter. The cortex generates dozens of possible movements every second · only some should reach the muscles. The basal ganglia decide which ones get through. Break the filter and you get either too much movement (chorea, ballism) or too little (Parkinsonian rigidity).
Wanted movement
Direct pathway lets it through · thalamus fires · cortex activates muscle
Tap a letter on the left half, or any pill above, to translate it to its full name.
The decoder rule. Six letters, six nuclei. The umbrellas (striatum, lentiform) and the white-matter ribbon (internal capsule) aren't nuclei · they're the names clinical medicine use to confuse you. Master the six chips and the umbrellas fall out automatically.
THE PATTERN
Lateral to Medial. Every Time.
One spatial rule eliminates 80% of wrong answers on basal ganglia questions.
The Lateral-to-Medial Cheat Code
On an axial CT at the level of the basal ganglia, structures line up lateral to medial like this:
Lateral = closest to the skull. Medial = closer to the midline/ventricles. The putamen is the most lateral of the deep gray nuclei. That's why it's the first thing the lenticulostriate arteries hit when they rupture.
Putamen = most lateral. If a board question describes a deep gray matter hemorrhage "lateral to the globus pallidus" or "medial to the insular cortex" · that's the putamen. Always.
INTERACTIVE ANATOMY
Axial Cross-Section
Tap any structure to see what it does and how it bleeds.
Tap a structure above or in the diagram to learn about it.
Coronal sections: caudate, putamen, and globus pallidus in their real positions. Source: Wikimedia Commons, CC BY-SA 3.0.
GROUPINGS
Groupings That clinical medicine Love
They test these names to confuse you. Know which structures group together and why.
Lentiform Nucleus = Putamen + Globus Pallidus
Named because they're lens-shaped together. "Lenti" = lens. This is a purely anatomical grouping · they sit next to each other and look like a lens on cross-section. They don't share a function.
Striatum = Putamen + Caudate
These two are actually the SAME structure embryologically · they got split apart by the internal capsule growing through them during development. They're still connected by thin bridges of gray matter (hence "striatum" = striped). This is a functional grouping · both receive input from the cortex (they're the "input" nuclei of the basal ganglia).
Corpus Striatum = Caudate + Putamen + Globus Pallidus
The whole package. "Corpus striatum" = the entire basal ganglia collection minus the subthalamic nucleus and substantia nigra. clinical medicine rarely test this name, but knowing the hierarchy helps: striatum (input) + GP (output) = corpus striatum.
Striatum = input. GP = output. Cortex sends motor plans TO the striatum (caudate + putamen) → striatum processes → sends signals through the GP → GP talks to the thalamus → thalamus projects back to cortex. It's a loop. Disrupting any step = movement disorder.
The nuclei labeled together: striatum, pallidum, and their neighbors. Source: Wikimedia Commons, CC BY 3.0.
ANATOMY DECODER
Striatum vs Lentiform · the Putamen Trick
One nucleus belongs to BOTH groupings. clinical medicine live for this trap.
Striatum = Caudate + PutamenLentiform = Putamen + Globus PallidusPutamen sits in BOTH
The putamen-in-both rule. Striatum is the C-shaped striped pair (Caudate + Putamen, input nuclei). Lentiform is the lens-shaped pair (Putamen + Globus Pallidus, the lens you can see on cross-section). The putamen is the only nucleus shared between the two groupings · which is why clinical medicine swap "lentiform" and "striatum" in stems to confuse you.
Spanish hook: putamen sounds like "puta · men" · think of it as the nucleus that shows up in TWO crowds. One foot in each group. The shared player.
Full basal ganglia roster (all 5)
Caudate · striatum input, wraps the lateral ventricle (C-shape)
Putamen · striatum input + lentiform · the only shared one
Globus pallidus · lentiform · main GABA output to thalamus
Substantia nigra · midbrain · sends dopamine to the striatum
Subthalamic nucleus · sits below the thalamus · regulates the indirect pathway
Trap: "Lentiform nucleus" vs "Striatum." If the stem says lentiform, the answer pair is putamen + globus pallidus. If the stem says striatum, the answer pair is putamen + caudate. The putamen is in both names, so don't pick "putamen" just because you recognize the word · pick the partner that finishes the grouping.
CIRCUIT SIMULATOR
The Gate Room
Knock out one part of the loop. Predict whether the gate jams open or slams shut, then watch it fire.
🎟
The Gatekeeper
Every movement your cortex dreams up has to clear my gate. Take out one of my crew and the gate misbehaves. Your call which way.
Step 1 · knock out a part of the loop
Step 2 · commit before you look
Does the gate jam open or slam shut?
excitesinhibits (GABA)dopamine
The pattern
Lesion
Circuit shift
Gate result
The whole game in one line. Anything that leaves the GPi underactive disinhibits the thalamus and gives you TOO MUCH movement (Huntington, hemiballism). Anything that leaves the GPi overactive silences the thalamus and gives you TOO LITTLE (Parkinson). Track the GPi, and the disease falls out.
DECISION TREE
Basal ganglia circuit: hyperkinetic vs hypokinetic
Follow the movement disorder to its circuit mechanism.
Movement disorder type?
Dopamine DEPLETED in striatum indirect pathway OVERACTIVE thalamus inhibited less cortical activation Parkinson disease pattern
Drug causes: typical antipsychotics (haloperidol), metoclopramide
One-line map. Huntington → caudate of the striatum (GABA loss · chorea). Wilson → putamen of the lentiform (copper deposits). Parkinson → substantia nigra (dopamine loss). Three diseases, three addresses, three loops broken in different places.
Trap: confusing Wilson and Huntington. Both are young adults with movement disorders, both hit basal ganglia · but Wilson is copper in the putamen with liver disease and KF rings, while Huntington is GABA loss in the caudate with chorea and family history (AD, CAG repeat). Wilson is treatable (chelation); Huntington is not. Pick the wrong structure and you pick the wrong disease.
THE STAKES
When Things Break
Every structure has a signature lesion. One structure, one disease · that's how clinical medicine test it.
Structure
Lesion
Clinical Finding
Putamen
Hypertensive hemorrhage (most common site)
Contralateral hemiparesis, hemisensory loss; may have aphasia (left) or neglect (right)
Globus Pallidus
Carbon monoxide poisoning
Bilateral GP necrosis on CT; parkinsonian symptoms, cognitive decline
Board Trap: "Hypertensive hemorrhage in the basal ganglia." They'll describe a hemorrhage "in the basal ganglia" and make you pick the exact structure. The location clues are: lateral = putamen (most common), medial near 3rd ventricle = thalamus (second most common). If they don't specify location and just ask "most common site," it's always putamen.
Board Trap: Confusing lentiform with striatum. If a question says "the lentiform nucleus," they mean the putamen + GP together · NOT the caudate. If they say "striatum," they mean putamen + caudate · NOT the GP. Getting the grouping wrong makes you pick the wrong structure.
🔑Hypertensive hemorrhage sites ranked: Putamen > Thalamus > Pons > Cerebellum. "PuTty Pons Cereals" · from most to least common.
THE HIGH-YIELD DETAIL
Why the Putamen Bleeds First
Charcot-Bouchard aneurysms. The name alone is board gold.
Weakened walls form Charcot-Bouchard microaneurysms
Microaneurysms rupture → hemorrhage into the putamen
Why the putamen specifically? Because the lenticulostriate arteries are direct branches off the MCA · they take the full force of systemic blood pressure without any buffer. They're tiny arteries feeding a big structure. That's the weak link.
Lenticulostriate arteries = "arteries of stroke." Jean-Martin Charcot called them this because they rupture so reliably in hypertensive patients. They supply the putamen, caudate head, and parts of the internal capsule · all common hemorrhage/infarct sites.
Board Trap: "Berry aneurysm" vs "Charcot-Bouchard aneurysm." Berry (saccular) aneurysms occur at the Circle of Willis (large arteries at the base of the brain) and cause subarachnoid hemorrhage. Charcot-Bouchard aneurysms occur in small penetrating arteries (lenticulostriate) and cause intraparenchymal hemorrhage. Different size artery, different location, different type of bleed.
DANGER ZONES
More Board Traps
The wrong answers that feel right · and how to kill them.
Trap: "Ex vacuo hydrocephalus" = Huntington disease. If imaging shows big ventricles + caudate atrophy, that's NOT obstructive hydrocephalus. The ventricles are big because the caudate shrank away. There's no blockage · the CSF just fills the space left behind. Treatment isn't a shunt; it's recognizing the neurodegenerative disease.
Trap: CO poisoning on CT. They show bilateral hypodensities in the GP. You think "bilateral basal ganglia infarcts from some vascular cause." But bilateral symmetric GP lesions = carbon monoxide poisoning until proven otherwise. CO exposure → hypoxia → GP is the first to die because it has the highest metabolic demand of the deep nuclei.
Trap: "Pure motor hemiparesis" = internal capsule, NOT putamen. A lacunar stroke in the posterior limb of the internal capsule gives you pure motor loss without sensory deficits. A putamen hemorrhage (much bigger) typically hits BOTH motor and sensory fibers, plus may cause aphasia or neglect. If the deficit is pure motor with nothing else, think lacunar infarct in the capsule.
🔑CO kills the Globus Pallidus. "CO-GP" · Carbon monOxide Goes to Pallidus.
TEST YOURSELF
Quiz
5 board-style questions, drawn at random from a bank of 26. All original.
THE ROGUES
Basal Ganglia Villain Cards
Each villain is a signature basal ganglia lesion. Tap to reveal the exact lesion rule.
🧨
The HTN Bomber
Sudden stroke in a hypertensive. Deep gray lesion, most lateral.
tap to flip
🧨 The HTN Bomber
Putamen = most lateral deep gray nucleus. Fed by lenticulostriate arteries (MCA branches). Chronic HTN causes Charcot-Bouchard microaneurysms in these tiny end-arteries. When they rupture, hemorrhage goes into the putamen first.
Break it down: Most common hypertensive hemorrhage = putamen. Lateral to GP + medial to insula = always putamen.
💨
The Silent Killer
Found in a running car. Bilateral symmetric deep gray lesions on CT.
tap to flip
💨 The Silent Killer
Carbon monoxide poisoning targets the globus pallidus specifically. The GP has the highest oxidative metabolic rate of the deep nuclei. CO binds hemoglobin 240x stronger than O2, creating tissue hypoxia. The GP dies first.
Break it down: Bilateral symmetric deep gray lesions = CO poisoning = GP necrosis. Not the putamen, not the caudate.
🕺
The Dance Killer
Chorea + dementia + psych symptoms. Family history. Box-car ventricles.
tap to flip
🕺 The Dance Killer
Huntington disease = caudate nucleus atrophy. The caudate head normally bulges into the frontal horn of the lateral ventricle. When it atrophies, the ventricles expand into the space (ex vacuo hydrocephalus). "Box-car ventricles" on imaging.
Sudden violent flinging of one limb. No weakness. No chorea.
tap to flip
🥊 The Wild Flinger
Hemiballismus = subthalamic nucleus (STN) lesion. The STN sends excitatory signals to the GPi, which inhibits the thalamus. Lose STN = GPi can't inhibit = thalamus unchecked = wild motor output. Contralateral to the lesion.
Break it down: Contralateral hemiballismus (violent flinging) = STN lesion. Lacunar stroke in elderly hypertensive is the most common cause.
🔥
The Burning Ghost
Sensory loss + severe burning pain. No motor deficit. Adjacent to 3rd ventricle.
tap to flip
🔥 The Burning Ghost
Thalamic stroke (2nd most common hypertensive hemorrhage site) causes contralateral hemisensory loss. After stroke, damaged thalamic nuclei can misinterpret normal touch as severe burning pain = Dejerine-Roussy syndrome. No motor deficit because motor fibers are in the internal capsule.
Break it down: Contralateral sensory loss + burning pain + no motor = thalamic injury = Dejerine-Roussy. Next to 3rd ventricle on imaging.
🛣
The Pure Motor Trap
Pure motor hemiparesis. No sensory loss. No aphasia. No neglect.
tap to flip
🛣 The Pure Motor Trap
Lacunar infarct in the posterior limb of the internal capsule. All corticospinal motor fibers are tightly packed here. A tiny stroke wipes out the entire motor output to one side with nothing else. White matter, not gray. Between thalamus (medially) and lentiform nucleus (laterally).
Break it down: Pure motor + equal face/arm/leg + no sensory = posterior limb IC lacunar. Not putamen (which has sensory + aphasia/neglect).
DIAGNOSTIC PATHWAY
Movement Disorder Localizer
Involuntary movements walk into the ED. Follow the branches to the structure.
A real basal ganglia bleed on noncontrast CT. Tap to enlarge. (Anatomy images sit inline with the structures they show.)
Noncontrast CT: acute basal ganglia hemorrhage. Source: Wikimedia Commons, CC BY 2.0.
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Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated July 5, 2026 at 11:43 AM ET
Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.
