Creutzfeldt-Jakob Disease on DWI MRI

Fig 1&2: Axial DWI MRI images of a 68-year-old man who presented with rapidly progressive dementia showed high signal intensity in the regions of cerebral cortex of the frontal and temporal lobes (arrowheads) and deep nuclei of basal ganglia (arrows). More subtle changes are also noted in the thalami. Findings are consistent with Creutzfeldt-Jakob disease.

Creutzfeldt-Jakob Disease (CJD)

• Progressive, fatal spongioform encephalopathy
• Transmissable disease
• Clinical: rapidly progressive dementia (<2>

MRI of CJD

• Distribution of abnormality: usually symmetric, deep gray nuclei (caudate head, putamen, thalamus), cerebral cortex
  
• Characters: high signal on T2 and FLAIR, restricted diffusion on DWI
  
• DWI may be the most sensitive imaging method for the early clinical diagnosis of CJD

Reference:
Shiga Y, et al. Diffusion-weighted MRI abnormalities as an early diagnostic marker for Creutzfeldt-Jakob disease. Neurology 2004;63:443-449.

Torus (Buckle) Fracture

Fig: Forearm radiograph shows a fracture as bulged cortex at the distal end of the radius. This is a classic torus (buckle) fracture.

Facts

• Axial loading on extremity with/without other forces (i.e. varus, valgus, hyperextension or hyperflexion)
• Failure of cortex on the compression side, resulting in fracture
  
• Torus (buckle) fracture of distal radius and ulna is most common fracture in lower forearm of young children
• Two appearances: 1) classic buckle fracture -- cortex bulges outward, 2) angled buckle fracture -- cortex angles inward (the second type is more difficult to appreciate)

Reference:
Jadhav SP, Swischuk LE. Commonly missed subtle skeletal injuries in children: a pictorial review. Emerg Radiol 2008 (November)

Biological Effects of Radiation Used in Imaging (3): Risks

Excess Risks of Mortality from Solid Cancer in Human

• Dose >100 mSv
• Dose 50-100 mSv
  
• Dose 10-50 mSv (i.e. to lung or breast in retrospective-ECG-gated cardiac CT, pediatric abdominal CT)
• Unclear risk if dose <10>

Natural effective dose of radiation received by general population = 3-4 mSv per year

Radiation risks

• Negligible (<0.1>
• Extremely low (0.1 - 1 mSv) - abdomen radiograph, lumbar spine radiograph
• Very low (1-10 mSv) - head CT, chest CT, abdomen CT (adult)
• Low (10-100 mSv) - multiphase CT
• Moderate (>100 mSv) - interventional procedures, repeat CT

Reference:
Verdun FR. Radiation risk: what you should know to tell your patients. Radiographics 2008 (September).

Hemangioblastoma

Fig 1: Axial MR image (T2) of a 57-year-old man presenting with headache shows a large T2 hyperintense mass in the left cerebellar hemisphere. The mass compresses the adjacent fourth ventricle.
Fig 2: Sagittal MR image (T1 with gadolinium) shows a focus of nodular enhancement at the wall of the mass, which is predominantly T1 hypointense. There is hydrocephalus.

Facts:

• Rare, benign neoplasm of endothelial origin
• Most are sporadic. Between 4 and 20% of patients with hemangioblastomas of the cerebellum or spinal cord have von Hippel-Lindau disease.
• Usually in cerebellum (hemisphere > vermis > medulla near area postrema)
• Most often have a firm mural nodule (near pial surface) associated with a glial-lined cyst. The cyst contains clear yellow fluid but hemorrhage can occur innto the cyst.

Imaging Appearance:

• Peripherally located cerebellar mass with central cystic region with peripheral enhancing nodule.
• Cystic portion of the hemangioma may be brighter than that of cerebral spinal fluid.
• In some cases, hemangioblastomas can be solid, mixed solid/cystic.
  

Reference:
Lee SR, Sanches J, Mark AS, et al. Posterior fossa hemangioblastomas: MR imaging. Radiology 1989; 171:463-468.

Subendocardial Fat in Myocardial Infarction

Fig: Axial contrast-enhanced CT image shows a curvilinear low attenuation in the subendocardial portion of the left anterior descending (LAD) coronary artery territory of the left ventricle. The patient had a history of remote myocardial infarction (MI).

Myocardial Fat

• Common entity, found histologically in 68% of ischemic heart disease patients and 84% of patients with history of MI.
• May result from inability of ischemic myocytes to metabolize fatty acids.
  
• Can be shown on cardiac MRI and CT.
• In one study, it was detected in 22% of cases and it was most commonly seen in LAD territory.
  

What does it mean?

• It is associated with greater infarct age
• Patients with myocardial fat had more severe regional wall motion abnormalities on echocardiography

Reference:
Ahn SS, et al. CT detection of subendocardial fat in myocardial infarction. AJR 2009;192:532-537.