Computed Tomography Test Computed Tomography (CT Brain) 3 — Questions and Answers
Question 1: On CT brain, the normal Hounsfield unit (HU) range for white matter is approximately:
- 20–30 HU (Correct answer)
- 0–10 HU
- 50–70 HU
- 80–100 HU
Correct answer: 20–30 HU
White matter typically measures 20–30 HU, slightly lower than gray matter (30–40 HU) due to its higher myelin lipid content.
Question 2: A ring-enhancing lesion in the brain on post-contrast CT with surrounding edema in an immunocompromised patient most likely represents:
- Toxoplasma abscess (Correct answer)
- Glioblastoma multiforme
- Meningioma
- Cavernous malformation
Correct answer: Toxoplasma abscess
Toxoplasmosis is the most common ring-enhancing lesion in immunocompromised (HIV/AIDS) patients, presenting as multiple ring-enhancing lesions.
Question 3: Which type of brain herniation is characterized by downward displacement of the cerebellar tonsils through the foramen magnum on CT?
- Tonsillar herniation (Correct answer)
- Uncal herniation
- Subfalcine herniation
- Transtentorial herniation
Correct answer: Tonsillar herniation
Tonsillar herniation occurs when increased posterior fossa pressure drives the cerebellar tonsils through the foramen magnum, compressing the brainstem.
Question 4: On CT brain, 'sulcal effacement' in one hemisphere most likely indicates:
- Cerebral edema causing compression of sulci (Correct answer)
- Normal aging-related brain atrophy
- Bilateral ventricular enlargement
- Calcification of the falx cerebri
Correct answer: Cerebral edema causing compression of sulci
Sulcal effacement occurs when edema or a mass expands the brain hemisphere, compressing and obliterating normal cortical sulci.
Question 5: A CT of the head shows enlargement of all four ventricles with periventricular hypodensity. The most likely diagnosis is:
- Communicating hydrocephalus with transependymal edema (Correct answer)
- Cerebral atrophy
- Bilateral subdural hematomas
- Diffuse axonal injury
Correct answer: Communicating hydrocephalus with transependymal edema
Communicating hydrocephalus causes symmetric dilation of all ventricles and periventricular hypodensity from transependymal CSF migration.
Question 6: The 'salt and pepper' or 'stippled' calcification pattern seen within a brain tumor on CT is most characteristic of:
- Oligodendroglioma (Correct answer)
- Meningioma
- Metastasis
- Ependymoma
Correct answer: Oligodendroglioma
Oligodendrogliomas classically show fine stippled or 'salt and pepper' calcifications on CT in up to 90% of cases.
Question 7: On CT brain, the falx cerebri normally appears:
- Mildly hyperdense relative to brain parenchyma (Correct answer)
- Hypodense relative to brain parenchyma
- Isodense to brain parenchyma
- Invisible without contrast
Correct answer: Mildly hyperdense relative to brain parenchyma
The falx cerebri is a dural reflection that appears mildly hyperdense on CT due to its fibrous dural composition and sometimes calcification.
Computed Tomography Test Computed Tomography (CT Brain) 3
On CT brain, the normal Hounsfield unit (HU) range for white matter is approximately: