The emergency physician should be adept at the interpretation of computed tomography of the head, particularly for life-threatening processes where awaiting a radiologist interpretation may unnecessarily delay care.
As with the approach detailed previously for imaging of the abdomen and pelvis, a similar structured method for interpretation of head imaging exists and follows the mnemonic “Blood Can Be Very Bad”.
- Acute: hyperdense (50-100HU)
- 1-2wks: isodense with brain
- 2-3wks: hypodense with brain
- Intraparenchymal Hemorrhage/Contusions
- Sudden deceleration of the head causes the brain to impact on bony prominences (e.g., temporal, frontal, occipital poles).
- Non-traumatic hemorrhagic lesions seen more frequently in elderly and located in basal ganglia.
- Intraventricular Hemorrhage
- White density in otherwise black ventricular spaces, can lead to obstructive hydrocephalus and elevated ICP.
- Associated with worse prognosis in trauma.
- Subarachnoid Hemorrhage
- Hemorrhage into subarachnoid space usually filled with CSF (cistern, brain convexity).
- Extracranial Hemorrhage
- Presence of significant extracranial blood or soft-tissue swelling should point examiner to evaluation of underlying brain parenchyma, opposing brain parenchyma (for contrecoup injuries) and underlying bone for identification of fractures.
- Circummesencephalic: CSF ring around midbrain and most sensitive marker for elevated ICP
- Suprasellar: Star-shaped space above the sella
- Quadrigeminal: W-shaped space at the top of the midbrain
- Sylvian: Bilateral space between temporal/frontal lobes
Evaluate the brain parenchyma, including an assessment of symmetry of the gyri/sulci pattern, midline shift, and a clear gray-white differentiation.
Evaluate the ventricles for dilation or compression. Compare the ventricle size to the size of cisterns, large ventricles with normal/compressed cisterns and sulcal spaces suggests obstruction.
Switch to bone windows to evaluate for fracture. The identification of small, linear, non-depressed skull fractures may be difficult to identify as they are often confused with sutures – surrogates include pneumocephalus, and abnormal aeration of mastoid air cells and sinuses. The Presence of fractures increases the suspicion for intracranial injury, search adjacent and opposing parenchyma and extra-axial spaces.
- Perron A. How to read a head CT scan. Emergency Medicine. 2008.
- Arhami Dolatabadi A, Baratloo A, Rouhipour A, et al. Interpretation of Computed Tomography of the Head: Emergency Physicians versus Radiologists. Trauma Mon. 2013;18(2):86–89. doi:10.5812/traumamon.12023.
As with the systematic approach preferred for the evaluation and management of other processes explored on this site, a similarly structured method for the interpretation of imaging commonly obtained in the emergency department may afford the same benefits – namely, the timely identification of pathology while avoiding costly missed diagnoses. In this post, I propose an approach to the interpretation of computed tomography of the abdomen and pelvis.
Start with the descending thoracic aorta
Follow the abdominal aorta down including its branches (celiac, SMA, paired renal arteries, IMA)
Continue to the bifurcation of the abdominal aorta to the left and right common iliac arteries
Start with the left and right femoral veins
Inferior Vena Cava
Follow the inferior vena cava up
The inferior vena cava gains contrast from the renal veins
The inferior vena cava empties into the right atrium
Solid Organs Down
Heart and Pericardium
Evaluate for the presence of a pericardial effusion or cardiomegaly
Heterogenous contrast-enhancement is normal
The tail of the pancreas lies in the hilum of the spleen
Evaluate the intrahepatic bile ducts for dilation or pneumobilia, portal venous system for gas, and liver parenchyma for vascular abnormalities or abscesses
Evaluate for radioopaque stones, pericholecystic fluid or surrounding fat stranding
A wishbone-shaped structure superior to the kidneys
Kidney and Ureter
Evaluate for hydronephrosis or hydroureter
Continue down into the pelvis; in a female patient the evaluation should include the uterus and adnexa
Having reached the inferior-most portion of the image following solid organs, move upward again from the rectum
Evaluate the sigmoid colon for diverticulitis
Continue following the sigmoid colon up the descending colon to the transverse colon and the hepatic flexure
Continue down the ascending colon to the cecum
At the cecum, attempt to identify a small tubular structure (the appendix) - evaluate for periappendiceal fat stranding, perforation or abscess
Start at the esophagus, evaluate for perforation or hernia
Continue to the stomach and duodenum
Evaluate the small bowel for obstruction (dilation, air-fluid levels)
Switch to lung window to evaluate the lung parenchyma and continue through the abdomen to identify intraperitoneal free air
Use the bone window to identify fractures or lytic lesions