Secondary Fahr-type brain calcifications: Imaging by CT or MR?

A 59-year-old female patient was admitted to the Department of Neurology with symptoms of impaired cognition and memory difficulties developed during the previous months and gradually deteriorated. The patient had known history of hypertension, renal failure and secondary hyperparathyroidism. Neurological examination was unremarkable. Mini mental score was 28/30.

Brain CT examination was performed revealing extensive symmetrical bilateral calcifications involving: the dentate nucleus and the cerebellum (Fig 1), the basal ganglia, the thalamus and the subcortical white matter of the occipital lobe (Fig 2), the body of caudate nucleus and the semi-oval centre (Fig 3).
Brain MR examination showed the calcifications as "paradoxical" high-signal areas on T1W-images (Fig 4). On T2W-images (Fig 5) and fluid-attenuated inversion recovery (FLAIR) images (Fig 6) the lesions appeared as hypo-intense signal foci along with extensive white matter hyperintensities. T2*-gradient images (Fig 7) portrayed the calcifications as low-signal intensity areas to a lesser extent than CT (Figs 1-3).

Non-idiopathic Fahr’s disease is commonly associated with endocrine disorders, particularly parathyroid glands diseases.
Middle-aged adults are most frequently affected, presenting neurological manifestations such as extrapyramidal symptoms or cerebellar dysfunction, speech difficulties and neuropsychiatric disorders. The diagnostic criteria of the disease includes neuroimaging that comprise of the visualisation of bilateral basal ganglia calcifications on brain imaging.

Calcification develops in the medial and adventitial wall of the arteries or veins, invading the perivascular space until it spreads to the neuron. These molecular changes occur as a result of impaired iron transport through defective channels, free radicals add up to damage the tissue and lead to calcium deposition which is then incorporated to proteins or bound to polysaccharides during the pathologic process. In addition, as the calcified areas augment, they tend to compress the vessels, thus causing a state of impaired blood supply to the brain parenchyma, injury of the neural tissue and further grow of calcifications. Concretions regularly involve areas that control movements such as basal ganglia, thalami, dentate nucleus, cerebral cortex, cerebellum and hippocampus [1].

The most appropriate tool to image brain calcifications is CT examination which is sensitive even to small quantities of calcium and allows earlier diagnosis of Fahr-type disease [1]. Brain MR either fails to depict or underestimates the calcium load. Yet, in MR sequences there are evident signal alterations of grey or white matter on T1 and T2-weighted images that may represent an early stage of the process. These T2-weighted hyperintensities could represent a subacute metabolic or inflammatory process, which may calcify in due course. It has been proposed that T2-weighted white matter hyperintensities correlate better with the clinical features than CT calcification load [2, 3]. In conclusion, calcifications are better demonstrated in the brain CT-examinations, but the MR imaging changes have a stronger correlation with the clinical symptoms and are more useful for diagnosis and accurate prognosis.