The most correct answer (d) is: isodense subdural hematoma

There is indeed evidence of moderate diffuse cerebral and cerebellar atrophy, as evidenced by the fact that the cerebrospinal fluid (CSF) spaces are all more noticeable, due to the brain tissue shrinking away (more black spaces). However, this is not the reason for this patient’s presentation. Further careful review of the CT image provided will reveal a subtle extra-axial fluid collection in the right lateral frontal region (left side of image), which has an almost identical CT density to the adjacent cerebral tissue (arrows, Figure 2), known as an isodense subdural hematoma (SDH). An SDH is a blood collection outside the brain, between the arachnoid and the dura mater. An isodense SDH generally indicates a subacute process where there has been some dilution and evolution of the blood products, which if left long enough, would exhibit a density similar to that of adjacent CSF (black). Those markedly hypodense chronic SDH collections are also termed “post-traumatic subdural hygromas.” Generally, acute SDHs are less than 72 hours old and are hyperdense (white) compared with the brain on CT scan. Subacute SDHs are 3-20 days old and are isodense or hypodense compared with the brain. Chronic SDHs are 21 days (3 weeks) or older and are hypodense compared with the brain. SDHs can also be of mixed density, such as when acute bleeding has occurred into a chronic SDH. In these cases, you may see layering of heavier acute white blood into the lower half of the SDH collection on the axial CT image. You will also notice subtle local mass effect on the subjacent brain tissue: the right lateral cerebral gryi (left side of image) are compressed and the sulcal CSF spaces are smaller in comparison to the contralateral normal side.

There is no identifiable history of head trauma in 25-50% of patients with chronic SDH. If a patient does have a history of head trauma, it’s usually mild. The average time elapsed between the occurrence of the head trauma and the diagnosis of chronic SDH is 4-5 weeks. Clinical presentation for chronic SDH is variable and often insidious, with symptoms that may include decreased level of consciousness, headache, difficulty with gait or balance, confusion or memory loss, motor deficit or aphasia. Chronic SDH may have a presentation similar to that of Parkinson's disease.

For patients presenting with acute or subacute SDH, surgical intervention by way of a burr hole is generally indicated to evacuate the clot, relieve intracranial pressure and eliminate or reduce presenting symptoms. Chronic SDH is a common treatable cause of dementia.

For the other choices given in this case, choice #1 (atrophy) is true but not the most likely cause of presentation. Choice #2 is wrong, as there is no hyperdense intracranial bleed present. The basal ganglia are unremarkable. Choice #3 is unlikely, with minimal white matter disease evident and CT is not the imaging modality of choice to make that diagnosis (that would be MRI). For choice #5, there is no evidence on the image of any space occupying lesions or other signs of intracranial metastases.

References:

1. Horn EM et al. Surg Neurol Feb 2006;65(2):150-3.
2. Lollis SS et al. Am J Neuroradiol 2006;27(1):74-5.
3. Muzii VF et al. J Neurosurg Sci 2005;49(2):41-6.
4. Cenic A et al. Can J Neurol Sci 2005;32(4):501-6.