CT Interpretation: Head

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”.

Normal Neuroanatomy

Brainstem
Posterior Fossa
High Pons
Cisterns
Ventricles

Blood: Blood

Density
Acute: hyperdense (50-100HU)
1-2wks: isodense with brain
2-3wks: hypodense with brain

Types/Locations

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.

Can: Cisterns


Evaluating the cisterns is important for the identification of increased intracranial pressures (assessed by effacement of spaces) and presence of subarachnoid blood.

  • 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

Be: Brain

Evaluate the brain parenchyma, including an assessment of symmetry of the gyri/sulci pattern, midline shift, and a clear gray-white differentiation.

Very: Ventricles

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.

Bad: Bone

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.

Example #1

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CT Head Interpretation

  • Ill-defined lesion in right parietal white matter with a large amount of surrounding vasogenic edema with midline shift and right uncal herniation.
  • Acute on subacute right extra-axial subdural hematoma.
  • Effacement of basilar cisterns.

Example #2

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CT Head Interpretation

  • Bilateral subacute subdural hematomas, left larger than right and associated with rightward midline shift.
  • Left lateral ventricle is partially effaced.

Example #3

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CT Head Interpretation

Subdural hematoma with significant herniation

References

  1. Perron A. How to read a head CT scan. Emergency Medicine. 2008.
  2. 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.

CT Interpretation: Abdomen/Pelvis

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.

Aorta Down

Thoracic Aorta

Thoracic Aorta

Start with the descending thoracic aorta

Abdominal Aorta

Abdominal Aorta

Follow the abdominal aorta down including its branches (celiac, SMA, paired renal arteries, IMA)

Aortic Bifurcation

Aortic Bifurcation

Continue to the bifurcation of the abdominal aorta to the left and right common iliac arteries

Veins Up

Femoral Veins

Femoral Veins

Start with the left and right femoral veins

Inferior Vena Cava

Inferior Vena Cava

Follow the inferior vena cava up

Infrahepatic IVC

Infrahepatic IVC

The inferior vena cava gains contrast from the renal veins

Right Atrium

Right Atrium

The inferior vena cava empties into the right atrium

Solid Organs Down

Heart and Pericardium

Heart and Pericardium

Evaluate for the presence of a pericardial effusion or cardiomegaly

Spleen

Spleen

Heterogenous contrast-enhancement is normal

Pancreas

Pancreas

The tail of the pancreas lies in the hilum of the spleen

Liver

Liver

Evaluate the intrahepatic bile ducts for dilation or pneumobilia, portal venous system for gas, and liver parenchyma for vascular abnormalities or abscesses

Gallbladder

Gallbladder

Evaluate for radioopaque stones, pericholecystic fluid or surrounding fat stranding

Adrenal

Adrenal

A wishbone-shaped structure superior to the kidneys

Kidney and Ureter

Kidney and Ureter

Evaluate for hydronephrosis or hydroureter

Bladder

Bladder

Continue down into the pelvis; in a female patient the evaluation should include the uterus and adnexa

Rectum Up

Rectum

Rectum

Having reached the inferior-most portion of the image following solid organs, move upward again from the rectum

Sigmoid

Sigmoid

Evaluate the sigmoid colon for diverticulitis

Transverse

Transverse

Continue following the sigmoid colon up the descending colon to the transverse colon and the hepatic flexure

Cecum

Cecum

Continue down the ascending colon to the cecum

Appendix

Appendix

At the cecum, attempt to identify a small tubular structure (the appendix) - evaluate for periappendiceal fat stranding, perforation or abscess

Esophagus Down

Esophagus

Esophagus

Start at the esophagus, evaluate for perforation or hernia

Stomach

Stomach

Continue to the stomach and duodenum

Small Bowel

Small Bowel

Evaluate the small bowel for obstruction (dilation, air-fluid levels)

Tissue-specific Windows

Lung Window

Lung Window

Switch to lung window to evaluate the lung parenchyma and continue through the abdomen to identify intraperitoneal free air

Bone Window

Bone Window

Use the bone window to identify fractures or lytic lesions

Try It Yourself

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CT Abdomen/Pelvis Interpretation

  • Cystic lesion in the inferior right lobe of the liver most consistent with hepatic abscess.
  • Multiple calcified gallstones in the gallbladder.