The lentiform fork sign is caused by vasogenic edema involving the white matter surrounding the basal ganglia, namely the internal and external capsules. On CT, this is seen as a hypodense rim. On MRI, it is better demonstrated and seen as a hyperintense rim on T2W and FLAIR images, with no restricted diffusion. In contrast, the putaminal abnormalities usually show restricted diffusion on MRI and are likely due to cytotoxic edema ^1,2.

This sign has been described in cases of metabolic acidosis from various causes, including uremic encephalopathy, drug-related (i.e., metformin), methanol or ethanol poisoning, as well as diabetic ketoacidosis.

The basal ganglia are usually involved in hypoxic, toxic, and metabolic disorders due to their high metabolic demand. Some authors have suggested that chronic diabetes mellitus also causes the basal ganglia to be more sensitive to uremic toxins and metabolic acidosis due to endothelial dysfunction ³.

This patient has underlying diabetes, hypertension, and end-stage renal disease. At the time of the scan, she was uremic with metabolic acidosis.