CT Scan Reveals a mass that may or may not be enhanced with use of contrast medium. On CT, low-grade gliomas may be isodense with normal brain parenchyma and may not be enhanced with contrast medium. Lesions in the posterior fossa may not be identifiable on CT scans. Consequently, CT findings alone may be insufficient for a diagnosis.

CT with contrast contrast = iodine contraindications: flows through cerebral vessels and leaks out in areas of blood-brain barrier breakdown order a CT with contrast when you’re worried about a focal lesion such as: tumor you will still miss lesions that can be seen only w/MRI but will increase yield substantially over plain CT contraindications: creatinine >1.5 (there are exceptions to this) iodine allergy (there are exceptions to this)

Contrast Enhancement

Post-con CT Plain CT Need: pic toxo w/ and w/o The plain CT shows a hypodense area on the left. The pattern of hypodensity is different than that seen with a stroke. Typically with MCA stroke, the hypodensity will extend to include the cortex. Here there is no cortical involvement. After contrast is obtained, an area of blood-brain barrier breakdown is evident in the center.The central area represents the lesion, the surrounding area of hypodensity is edema. This patient was HIV + and has toxoplasmosis.

MRI Magnetic resonance imaging (MRI) is more sensitive than CT for confirming the presence of a brain tumor. On T1-weighted MRI scans, a brain tumor appears as a mass lesion that may or may not be enhanced with contrast medium

Pre-contrast Post-contrast Shown here is a meningioma. While in this case, the mass is well seen even prior to contrast, it still is isodense to brain. Often, a mass cannot be well seen until it enhances with gad. This gives clues as to the type of mass. Meningiomas tend to be uniformly brightly enhancing though they are benign tumors.