Small Vessel Disease: Given the patient's age and the presence of hypoattenuation in the deep white matter on the CT scan, small vessel disease is a likely cause. This condition is common in the elderly and can lead to cognitive decline, gait disturbances, and increased risk of falls and syncope due to cerebral microangiopathy.

Chronic Subdural Hematoma: Although less common, a chronic subdural hematoma could present with similar symptoms, especially in the elderly after a fall. The hypoattenuation could be misinterpreted, and a hematoma might not always be immediately apparent on a non-contrast CT.
Normal Pressure Hydrocephalus (NPH): NPH can cause gait disturbances, dementia, and urinary incontinence. While the CT findings of mild generalized atrophic changes could be seen in NPH, the presence of hypoattenuation in the deep white matter is less typical but could be related to associated small vessel disease.
Cerebral Amyloid Angiopathy: This condition, characterized by the deposition of amyloid beta in the walls of small to medium-sized blood vessels in the brain, can lead to lobar hemorrhages but might also present with white matter changes due to chronic ischemia.

Subarachnoid Hemorrhage: Although the CT scan did not specifically mention blood in the subarachnoid space, a small or chronic subarachnoid hemorrhage could potentially be missed, especially if it is not acute. This diagnosis is critical because it requires immediate intervention to prevent further bleeding or to treat any associated aneurysms.
Brain Tumor: A brain tumor could cause focal neurological deficits, seizures, and increased intracranial pressure leading to syncope. While the described CT findings are not typical for a tumor, certain types like gliomatosis cerebri could present with diffuse white matter changes.
Cerebral Vasculitis: This is an inflammation of the blood vessels in the brain and can present with a wide range of symptoms including stroke, seizures, and cognitive decline. It is crucial to consider this diagnosis due to its potential for severe consequences if left untreated.

CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy): This is a rare hereditary condition leading to stroke and dementia. It typically presents at a younger age but could be considered in the differential for white matter changes, especially if there's a family history.
Posterior Reversible Encephalopathy Syndrome (PRES): Although typically associated with hypertension, eclampsia, or certain medications, PRES could present with similar white matter changes. It is usually reversible with appropriate management.
Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS): A rare mitochondrial disorder that can cause strokes, seizures, and dementia. It is more common in younger individuals but could be considered in the differential for unexplained white matter changes and neurological symptoms.