10-15 Neuroimaging Flashcards
Systematic Approach to Head CT Interpretation
- Know normal - identify the normal structures in each slice, considering age of pt and symmetry of image
- Determine whether lesion is in the brain (intraaxial) or outside (extraaxial)?
- Does lesion take up space (e.g. mass, edema, hematoma) or is there loss of tissue volume (e.g. encephalomalacia, atrophy)?
- Is there edema? If so, is it cytotoxic and vasogenic?
Age differences in brain CT appearance?
babies - more shallow sulci/fatter gyri, larger ventricles, less mature
older folks - smaller size is normal, deep sulci
What are three different CT windows?
Bone, Stroke, Soft Tissue
Intraaxial vs. Extraaxial masses
Intraaxial - push gyri out making sulci more shallow (see less CSF between cortex & skull)
extraaxial - see increased CSF space, displaced veins that are more medial then they ought be
Lesions that take up space vs. lesions causing loss of tissue volume
lesions that take up space - shrunken ventricles, midline shifted, sulci crowded
loss of tissue volume - ventricles larger, no midline ∆, sulci wider
cytotoxic vs. vasogenic edema
- -appearance
- -etiology
- -pathophys
cytotoxic edema
- -appearance: loss of grey/white difference
- -etiology: Stroke, stroke, stroke (encephalitis, tumor can mimic)
- -pathophys: Cortical cell death —> cortex less dense
vasogenic edema
- -appearance: accentuated grey/white difference
- -etiology: Tumor, inflamm disease, HTN
- -pathophys: Leaky capillaries —> edema spreads in WM
imaging test of choice in suspected acute stroke? why?
non-contrast CT of the head
- -stroke is a CLINICAL DIAGNOSIS
- -CT is fast & will r/o hemorrhage or stroke mimic that would contraindicate tPA
What will you see in a stroke window, non-contrast CT of the head in a stroke patient? What causes these findings?
- -hopefully nothing, no CT ∆s in first 6-24 hrs s/p CVA
- -Afterwards, 4 SIGNS SEEN:
1. Dense middle cerebral artery = clot
2. Loss of gray-white differentiation*
3. Loss of insular ribbon*
4. Effacement of sulci and loss of basal ganglia* - Signs of cytotoxic edema! The hallmark of stroke!
Gold Standard to ID dead brain s/p CVA (after emergency is over and pt is stable)
–specificity? false positives?
diffusion-weighted MRI
- -positive w/in minutes and stays + for 2 wks s/p
- -Fairly specific for stroke; False (+) with brain abscess, hemorrhage, MS
Head trauma: Who should get imaged?
FYI only–NEW ORLEANS HEAD CT RULES:
1.LOC or post-traumatic amnesia if one or more (+):
HA, vomiting, age >60, drug/Etoh, short-term mem def, physical evidence of trauma above clavicle, sz, GCS65, physical evidence of basilar skull fracture, GCS3 feet or 5 stairs)
–100% sensitive at IDing pts in whom CT abnormalities are present (but only 10-25% specific, still lots getting scanned that didn’t need it)
Head trauma: What are the common intracranial injuries identified in trauma patients?
1 Epidural Hematoma 2 Subdural Hematoma 3 Traumatic Subarachnoid Hemorrhage 4 Brain Contusion 5 Diffuse Axonal Injury
Where is the epidural space?
space is between the dura*/periosteum (which are fused) and naked bone
*Reflections of dura form venous sinuses, for this reason, epidural hematomas generally don’t cross sutures
subdural space + review of arachnoid anatomy
Potential space between arachnoid and dura
The arachnoid matter : Oppose to the dura, Tightly bound at venous sinuses due to arachnoid granulations, and has cobweb-like projections connecting it to the pia mater
subarachnoid space + review of pia anatomy
space between pia and dura that CONTAINS THE CSF
recall that pia mater is closely applied to cortex and follows all contours of the brain
Facts about epidural hematoma (EDH)
EDHs:
- bi-CONVEX/lens-shaped
- ARTERIAL bleed that STRIPS THE DURA off of the skull bone
- doesn’t cross suture lines
- 90% w/ skull fx —> MIDDLE MENINGEAL ARTERY
- usu on COUP side
- generally better prognosis
- neurosurg emerg —> burr hole that shit
Surgical mgmt of EDH
- -EDH>30cc’s should be evacuated regardless of GCS
- -EDH 8 without focal deficit can be nonoperatively managed
- -If acute EDH and GCS <9 with anisocoria*, evacuate ASAP
*(unequal pupils)
Facts about subdural hematomas
SDHs:
- -Hyperdense crescentic* collection
- -VENOUS —> tearing of bridging veins
- -May extend along falx and tentorium (contiguous)
- -Usu. counter coup, but can be coup
- -Young/old patients
- -Worse prognosis than EDH
- -Midline shift and thickness important features
- -can eventually cause subfalcine or transtentorial herniation
*crescent-shaped vs. lenticular in epidural
Surgical Mgmt of SDH?
- -Acute SDH >10mm thickness or midline shift >5 mm should be evacuated
- -All patients with acute SDH and GCS<5mm midline shift should have evacuation if GCS decreases by 2 points or more, increased ICP or fixed and dilated or asymmetric pupils
Assessing midline shift
- -Done at level of foramen of Monroe*
- -Midline shift = (A / 2) - B
- -5mm of shift is tipping point where surgery often warranted
*connects the paired lateral ventricles with the third ventricle
Subarachnoid hematoma (SAH)
SAHs:
- -trauma = #1 cause of SAH
- -No specific treatment
- -Are related to outcome – severe head injury mortality is 2X in severe head injury with SAH
- -VENOUS: Tearing of veins in subarachnoid space
- -Can be isoloted
- -If >5mm in thickness, worse prognosis
Contusions
–types? when will they appear on CT? mgmt? most common site?
- -Hemorrhagic or non-hemorrhagic
- -Often get bigger/better-defined over 2-3 days
- -If large hematoma, may need evacuation
- -Most common in anterior/inferior frontal lobes and anterior temporal as brain hits/slides over rough bone surfaces
- -Can be coup or contra-coup
Diffuse axonal injury
- -what is it?
- -pt presentation?
- -CT presentation?
- -It is a shearing injury of axons (Most not directly injured, but cascade set up that leads to cell death over 24 hours—>messages go back to brain re: apoptosis)
- -pt presents w/ low GCS
- -CT can be normal initially (50-80%); Gray-white interface, corpus callosum, midbrain (dorsolateral)
CT vs MRI in setting of head trauma?
¡Nearly always get CT first!
–CT accurately identifies all surgically important lesions
MRI, however, is more sensitive (fewer false negatives) to a number of lesions
– 30% more SDH and EDH
– 50% more contusions
– 50-80% more axonal injury
Use MRI on pts who continue to have unexplained deficits
Coup vs. Contracoup
coup = site of impact contracoup = opposite site of impact
**always check both areas throughly on PE and CT
