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Imaging of Traumatic Brain Injury: Pearls and Pitfalls

This was presented at the 51st Annual Scientific Meeting of the Royal College of Radiologists of Thailand.

Renal Artery Variants in Patients with Normal Renal Function

3D volume rendered CT image shows a 2nd right renal artery (arrows) arising from the right common iliac artery

Facts

• "Normal" renal arterial arrangement = single bilateral renal arteries with hilar segmental branching. This occurred in 46% of cases in a landmark angiographic report published in 1978
• Normally, no intrarenal arterial anastomoses are present. Each artery represents an end artery -- interruption results in infarction of that segment
• Variations include double renal arteries, triple renal arteries, pre-hilar segmental branching, fetal lobulation and exaggerated size difference (greater than 2 cm). 
• Most common variations are multiple renal arteries followed by pre-hilar segmental branching

Knowledge of Renal Vascular Variations is Important For:

• Renal transplantation
• Renovascular hypertension
• Vascular reconstruction for congenital and acquired lesions
• Reconstructive surgery for abdominal aortic aneurysms

Our case: Double right renal artery with the smaller branch originating from the common iliac artery

Reference:

- Harrison, Jr., et al. Incidence of anatomical variants in renal vasculature in the presence of normal renal function. Ann Surg 1978;188:83-89.

- Ozkan U, et al. Renal artery origins and variations: angiographic evaluation of 855 consecutive patients. Diagn Interv Radiol 2006;12:183-6.

Vertebral Artery Hypoplasia

Curved reformat of the normal-caliber right vertebral artery showing all 4 segments of the artery. 

Curved reformat of the left vertebral artery shows diffuse, small caliber of the artery.

Facts:

• Operational definitions are either 1) asymmetrical ratio of or greater than 1:1.7, or 2) discrepancy of greater than 2 mm diameter
• Prevalence 2%-6% of population (from autopsy and angiographic series)

Clinical Relevance

• Posterior circulation ischemia: hypoplasia leads to reduction of posterior circulation blood flow velocity therefore has a negative role in occlusion of major cerebral arteries
• Migraine with aura and vestibular neuronitis: hypoplasia is believed to be associated with regional hypo perfusion and complex neurovascular consequences

Reference:

Chuang YM, Chan L, Wu HM, et al. The clinical relevance of vertebral artery hypoplasia. Acta Neurol Taiwan 2012;21:1-7.

Fatty Liver

Axial "in-phase" MR image shows increased signal intensity of the liver.

Axial "opposed-phase" MR image shows decreased signal of the entire liver when compared with the same areas on in-phase image. 

Facts

• Triglyceride accumulation within cytoplasm of hepatocytes
• Can be due to alcoholic liver disease, nonalcoholic fatty liver disease, viral hepatitis, drugs
• May progress to steatohepatitis and cirrhosis
• Avoid the use of "fatty infiltration of the liver", which is misleading because fat deposition in Fatty Liver is in hepatocytes - rarely in other cell types
• Sensitivity/specificity for detection:
• Ultrasound = 60-100% / 77-95%
• Non-contrast CT = 43-95% / 90%
• Chemical-shift MRI = 81% / 100%

MR Imaging

• Because protons in water and fatty acid molecules precess in different resonance frequency, proton chemical shift imaging can be utilized to image this difference
• If images are obtained when fat and water protons are "in-phase", their signals are additive (brighter). If they are "out-of-phase", their signals cancel each other (structure becoming darker)
• Amount of hepatic fat can be quantified by assessing the degree of signal loss

Reference

Hamer OW, Aguirre DA, Casola G, et al. Fatty liver: imaging patterns and pitfalls. Radiographics 2006; 26:1637-1653.