Head CT Interpretation in the ED: The Complete Primer Brian A. Stettler, MD Assistant Professor Department of Emergency Medicine University of Cincinnati

Objectives Discuss the utility of Head CT Discuss what Head CT will miss Review basic interpretation of the Head CT Discuss a few specific disease processes 54 2 54

Clinical History CC: Headache and weakness HPI: 67 year old female with several months of dull headaches relieved by Tylenol and subjective “dizziness” without falls. Symptoms worsened today about 2 hours ago and she now complains she cannot walk secondary to dizziness 54 3 54

ED Presentation PMHx: DM, HTN, CAD Meds: Atenolol, HCTZ, ASA, Insulin All: NKDA SocHx: 1PPD, Occasional Etoh, denies drugs ROS: mild anorexia, weight loss approx 5 lbs over past month, o/w neg 54 3 54

ED Presentation PE: 176/94, 65, 16, 98.8, 93% RA Gen: alert and conversive, sl uncomfortable appearing HEENT: WNL Pulm: sl wheezes, otherwise WNL CV: WNL Neuro: strength 4/5 throughout, gait unsteady without overt ataxia, no deficits to cranial nerves 54 3 54

Points of Discussion In addition to other labs, a non-contrast head CT is ordered How is this study interpreted? What findings affect the treatment of the patient? What findings portend a bad outcome for the patient? 54 2 54

Non-contrast Head CT The most common neuroimaging tool employed in the ED Performed in seconds, usually read in minutes No IV access required Available 24 hours/day in most EDs No real contraindications Good sensitivity and specificity for many disease processes 54 2 54

Non-contrast Head CT Benefits: Gold standard in assessment for acute hemorrhage Very good at documenting mass effect and herniation Will visualize acute ischemia, neoplasm, localized intracranial infection Good at visualizing skull fracture 5 17

Non-contrast Head CT Drawbacks Poor at visualizing disease in the posterior cranial fossa, especially ischemia Poor at diagnosing intracranial mass that does not have significant mass effect Sensitivity is not high enough to completely eliminate SAH Will miss delayed disease, such as delayed SDH 5 17

Head CT Interpretation Scout, assessment for adequacy Quick look Detailed look (force yourself) Extra-axial blood Mass effect Ischemia Ventricles Vessel density Bone windows Extras (sinuses, mastoids) Compare to old 54 54 2

Head CT Interpretation Look at the scout Adequate study? Minimize motion Subject to artifact from metal 5 17

Head CT Interpretation Quick look Get the gestalt Assess for gross abnormalities 54 2 54

Head CT Interpretation Extra-axial hemorrhage Epidural hematoma Subdural hematoma Subarachnoid hemorrhage Intracerebral hemorrhage Intraventricular hemorrhage 54 2 54

Epidural Hematoma “Lens” shaped Does not cross suture lines Typically acute or hyperacute Frequently associated with mass effect 54 2 54

Subdural Hematoma Located along calvarium, falx, tentorium Crosses suture lines, usually spreads more extensively than epidural Acute 54 54 2

Subdural Hematoma Can be acute, subacute, or chronic Density on CT helps to age hematoma Can frequently be a mix of ages Can have mass effect that ranges from none to severe Subacute 54 54 2

Subdural Hematoma Not all SDH are bright white Chronic Not all SDH are bright white MUST follow gyri/sulci to edge of calvarium on every cut Falx may be calcified but should be thin Osborn, Diagnostic Imaging Brain 2004 54 54 2

Subarachnoid Hemorrhage Can be present in cisterns, around gyri and sulci Almost always acute Sensitivity of NCHT Not well known or agreed upon Probably in the high 90’s early Decreases as time progresses from onset of symptoms 54 2 54

Subarachnoid Hemorrhage Source: Post-traumatic Aneurysmal AVM Other Hounsfield units Blood is 50-100 (80) 54 2 54

Intracerebral Hemorrhage Location can be anywhere in the parenchyma Can be caused by hypertension, AVM, amyloid Typically present with headache, focal neurologic findings, AMS, N/V 54 2 54

Intracerebral hemorrhage CT findings that affect outcome Volume of hemorrhage Location of hemorrhage (supra vs infratentorial) Presence of intraventricular hemorrhage Also describe: Presence of midline shift Presence of herniation Presence of hydrocephalus 54 2 54

Volume of Hemorrhage (A x B x C)/2 A and B are perpendicular dimensions in the slice that shows the maximal amount of hemorrhage C is the total number of slices that show hemorrhage x the slice thickness Ex: 4cm x 5.5 cm by (8 x 5mm slices)/2 4 x 5.5 x 4/2 = 45cc 54 2 54

Mass Effect and Midline Shift Mass effect can be local or generalized When generalized, typically seen as shift of the midline structures away from the area of mass effect Midline shift Use drawing tools to draw line down center of skull Measure from midline structure (pineal gland, falx, septum pellucidum) to line drawn 54 2 54

Herniation Herniation is an ominous sign on CT Types Uncal (3rd nerve palsy – the “blown pupil”) Transtentorial Sub-falcine Tonsillar Look for structures where they should not be

Tying it Together Spontaneous ICH Supratentorial (L basal ganglia) Approx 45cc 8mm of midline shift Evidence of uncal herniation 54 2 54

Trauma - Contusions Patchy hemorrhage contained to the superficial grey matter Frequently associated with local edema Caused by brain impact to bone Locations most commonly temporal lobes and frontal, but can occur anywhere 54 2 54

Trauma - Contusions Contusions frequently evolve from small petechiae to large areas of edema and hemorrhage over the course of 1-2 days Osborn, Diagnostic Imaging Brain 2004

Ischemia Very early CT typically negative Early findings Loss of grey-white differentiation Insular “ribbon” Basal ganglia/internal capsule Effacement of ventricles and local mass effect Hyperdense artery 54 2 54

Ischemia ASPECTS Larger areas of grey-white changes on initial CT have worse outcomes Score < 7 had OR 82 for worse functional outcome Barber, Lancet 2000 54 54 2

Being Thorough Use bone windows on every trauma Don’t forget the extras Sinuses, mastoid air cells Air where it shouldn’t be Orbits Old infarcts If abnormal, look for an old CT 54 2 54

Case Follow-up Pt’s CT showed a small, ill-defined parenchymal hemorrhage Follow-up MRI showed multiple enhancing lesions suspicious for mets Pt undergoing treatment for metastatic lung CA 54 2 54

Head CT - Conclusions Scan early and often Beware the lurking slit subdural Contusions can be tiny – at first Ischemia can be subtle You still can’t completely trust the negative SAH CT Negative early doesn’t always mean negative late – and vice versa 5 17

Head CT - Conclusions Useful imaging screening tool for many life-threatening neurologic processes May miss early findings in hemorrhage or ischemia Interpretation must be done thoroughly The same way every time Assess not only primary pathology, but factors contributing to outcome 54 2 54

Questions?