Epidural, subdural, subarachnoid. Same skull, three different layers, three different vessels, three different death notices. By the end you will read the CT before they tell you the trauma.
A 22-year-old college boxer takes a hard left hook to the right temple. He drops to the canvas, briefly unresponsive, then sits up confused but talking. Ringside doc clears him to walk to the locker room. 30 minutes later his cornerman finds him slumped on the bench, clinical subjectose, with a blown right pupil and a fixed gaze deviated down and out.
What ruptured?
Temple hit + lucid interval + rapid herniation = epidural hematoma from a torn middle meningeal artery.
The pterion is the thinnest spot on the skull (where frontal, parietal, temporal, and sphenoid bones meet) and the middle meningeal artery runs right under it. Punch the temple, you crack the pterion, you tear the MMA. Arterial pressure means fast filling. The lucid interval is the gap before the lens-shaped clot is big enough to herniate the temporal lobe through the tentorium, which crushes CN III against the petrous ridge: blown pupil + down-and-out eye.
Bridging veins tear in subdural bleeds (slow, crescent, no lucid interval). ACOM/PCOM aneurysms cause subarachnoid hemorrhage (thunderclap headache, no preceding trauma). Charcot-Bouchard and lipohyalinotic vessels rupture into brain parenchyma (basal ganglia, pons), classically in chronic hypertensives, not boxers.
Map · Tap a bleed
Three layers, three bleeds
Coronal slice through the skull. Tap a bleed to see exactly which anatomic space it occupies. Same hemisphere, three completely different addresses.
Epidural · Between skull and dura
The dura is glued to the inner table of the skull along the sutures. Arterial blood from the torn middle meningeal artery pries the dura off the bone wherever the glue is weakest, but it cannot cross the suture lines. Result: a tight, biconvex lens of high-pressure blood sitting on the dura.
Bleed 1 · Arterial · Fast
Epidural Hematoma
High-pressure arterial bleed pinned between bone and dura. The clock starts at the temple punch.
Middle Meningeal Artery · Pterion Fracture
Branch of maxillary artery · from external carotid
Vessel
Middle meningeal artery. Branch of the maxillary artery, off the external carotid. Runs in a bony groove on the inside of the temporal bone, right under the pterion.
Trauma
Pterion fracture · the thinnest spot on the skull (frontal + parietal + temporal + sphenoid junction). A baseball, bat, or fist to the temple cracks it and the bone edge slices the artery.
Clinical course
Lucid interval. Patient is knocked out, wakes up alert, then crashes in minutes to hours as the lens balloons and herniates the uncus over the tentorium.
CT fingerprint
Lens-shaped (biconvex) hyperdensity that does NOT cross sutures. The dura is stuck to the suture lines, so the blood has to stop where the glue holds.
Speed
Arterial pressure means fast accumulation. Surgical emergency · minutes matter, hematoma evacuation through a burr hole or craniotomy.
Memory hook
EPI = Eye-shaped lens. Or: Hi-ED = high-pressure ED visit.
Biconvex clot pinned between skull and dura. The dura cannot peel past the sutures, so the blood swells inward instead.
Board Pearl
The lucid interval is the trap. Examiners give you a head injury, knock the patient out, wake him up clear, and then ask what happens next. If the stem mentions temple, pterion, or boxer/baseball plus a brief recovery before deterioration, the answer is epidural until proven otherwise. CN III palsy (blown pupil, eye down and out) means uncal herniation is already happening · call neurosurgery before you finish writing the note.
Bleed 2 · Venous · Slow
Subdural Hematoma
Low-pressure venous bleed that follows the inner curve of the skull. The bridge breaks slowly.
Bridging Veins · Cortex to Dural Sinus
The slow, sneaky, suture-crossing bleed
Vessels
Bridging veins running from the cortex up to the superior sagittal sinus. They stretch across the subdural space · once the brain shifts or shrinks, they snap.
Trauma
Deceleration injury (whiplash, shaken baby), or a fall in an elderly patient whose atrophic brain has stretched the bridging veins to the breaking point. Alcoholics get a double dose · atrophy plus falls.
Clinical course
Gradual. Venous pressure is low, so the bleed fills slowly · acute (hours), subacute (days), or chronic (weeks). Confusion, headache, gait change, sometimes weeks after the fall the family barely remembers.
CT fingerprint
Crescent-shaped hyperdensity that CROSSES suture lines. The blood sits beneath the dura, free of its suture attachments, so it can spread along the entire inner table.
Who you should suspect
Shaken babies · always think nonaccidental trauma. Fallen elders on aspirin or warfarin. Alcoholics with mystery confusion.
Memory hook
SUB = Slow + Senior + Shaken. Crescent moon, not lens.
Crescent moon of venous blood hugging the inner table from one suture line to the next. Atrophic brain underneath leaves bridging veins overstretched and tear-prone.
Board Pearl
Old grandma falls last week, family thinks she is "just confused." That is a subacute subdural until you prove otherwise. Get a non-contrast head CT, look for the crescent. Bilateral subdurals in an infant under 1 year with retinal hemorrhages = nonaccidental trauma, full social work and skeletal survey. The acute subdural is hyperdense (bright white), chronic is hypodense (dark), subacute is isodense (sneaky · look for asymmetry and effaced sulci).
Bleed 3 · Aneurysm · Catastrophic
Subarachnoid Hemorrhage
A berry blew up in the Circle of Willis. Blood floods the CSF space and the patient feels it like a bat to the head.
Berry Aneurysm · Circle of Willis
Worst headache of life · nuchal rigidity · xanthochromia on LP
Source
Berry (saccular) aneurysm rupture in the Circle of Willis. Most common location: ACOM (anterior communicating artery, ~30%).
Risk factors
Hypertension (main). Polycystic Kidney Disease (ADPKD), Ehlers-Danlos type IV, smoking, cocaine, family history of aneurysms.
Clinical
Thunderclap headache · "worst headache of my life," sudden, max severity in seconds. Plus nuchal rigidity, photophobia, vomiting, transient loss of consciousness, sometimes seizure.
ACOM trap
An ACOM aneurysm sits right above the optic chiasm. If it ruptures or compresses, you get bitemporal hemianopia · same field cut as a pituitary tumor.
PCOM trap
A PCOM aneurysm sits next to CN III. The parasympathetic fibers ride on the outside of the nerve · pressure causes a CN III palsy: down-and-out eye, ptosis, blown pupil.
Workup
Non-contrast CT head emergent (sensitivity drops after 6 hours). If CT negative + high suspicion, do an LP looking for xanthochromia (yellow CSF from RBC breakdown to bilirubin).
Treatment
Nimodipine (calcium channel blocker) to prevent vasospasm and delayed ischemia. Definitive: surgical clipping or endovascular coiling of the aneurysm.
Memory hook
SAH = Sudden, Awful Headache. PCKD = "the kidneys come with extra grenades in the head."
Inferior view of the Circle of Willis. ACOM aneurysm sits right above the optic chiasm · rupture bleeds into the suprasellar cistern, compression cuts the chiasm. PCOM aneurysm presses on CN III as it exits.
Board Pearl
A thunderclap headache with a negative CT is the trick. After 6 hours, CT sensitivity drops to ~85%, so a negative CT does NOT rule out SAH. Do an LP and look for xanthochromia. If the patient has bilateral flank pain, family history, hypertension at 35, think ADPKD and screen the head with MRA. Anyone with sentinel headaches in the weeks before the big one had a warning leak and was missed.
CT · Three shapes
Three CT fingerprints, side by side
Each bleed paints a different shape on the axial CT. Memorize the silhouettes · you will be asked to match shape to mechanism on every neuro shelf.
Lens
Epidural
Biconvex, hugs one bone segment, does not cross sutures.
Crescent
Subdural
Concave moon, spans the whole hemisphere, crosses sutures, may push the falx.
Star
SAH
Blood traces the basal cisterns and sylvian fissures · "star" or "spider" of CSF blood.
Bonus · Intracerebral hemorrhage: blood inside the brain itself, most often in the basal ganglia/putamen from a ruptured Charcot-Bouchard aneurysm on a lipohyalinotic small vessel in a chronic hypertensive. Lobar bleeds in an elderly patient instead point to cerebral amyloid angiopathy.
LP · Yellow CSF
Xanthochromia: three causes
If the CT is negative and you tapped the spine, the LP tube turns straw-yellow when red cells have been sitting long enough to break down to bilirubin. Three classic causes, in lecture order.
Why CSF turns yellow
RBC sits in CSF → hemoglobin spills out → macrophages chew it up → bilirubin pigment stains the CSF straw-yellow. Takes about 6-12 hours to develop · useful when the head CT is already negative.
SAH
Berry aneurysm bursts · RBC breakdown into bilirubin is the classic source of xanthochromia.
IVH
Intraventricular hemorrhage · blood drains into CSF circulation, same bilirubin pathway.
Mechanism: RBC in CSF → hemoglobin leaks out → macrophages convert it to bilirubin → CSF becomes straw-yellow. Less common causes you might still see on a test: traumatic LP if the tube sits for hours before analysis, newborn with severe hyperbilirubinemia, very high CSF protein from chronic inflammation.
Side by side
The Big Three at a glance
Vessel, shape, trauma, time course, treatment. The five columns you should be able to fill in on demand.
Bleed
Vessel
CT shape
Trauma
Time
Tx
Epidural
Middle meningeal artery
Lens, does not cross sutures
Temple/pterion fracture
Minutes to hours · lucid interval
Emergent craniotomy
Subdural
Bridging veins
Crescent, crosses sutures
Deceleration, shaken baby, elderly fall
Hours to weeks · acute/subacute/chronic
Evacuation if symptomatic or large
SAH
Berry aneurysm (ACOM most common)
Star of blood in basal cisterns
Spontaneous · HTN, ADPKD, EDS, smoking
Seconds · thunderclap
Nimodipine + clip or coil
Test · Six vignettes
Drill it
Six clinical vignettes, A through E. Tap an answer to see the explanation: clue, chain, and the high-yield detail.
clinical Walkthrough
clinical Walkthrough
Original clinical vignettes. Shuffled, never-repeat, full explanations for every choice.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated June 30, 2026 at 2:05 AM ET
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