Lentiform Fork Sign in Metabolic Acidosis

The basal ganglia are susceptible to hypoxic, toxic, and metabolic disorders because of high metabolic demand.1 Uremic encephalopathy commonly targets the basal ganglia, with a typical pattern of lentiform involvement, known as the lentiform fork sign, on T2 and fluid-attenuated inversion recovery (FLAIR) sequences of brain magnetic resonance imaging (MRI).2 MRI of the brain in two of our patients with uremic encephalopathy revealed this sign. Our first patient, a 61-year-old male, a living kidney donor with no other pertinent past medical history, presented with fever and vomiting for 5 days and an episode of generalized tonic–clonic seizure on the day of hospitalization. No focal neurological deficit was detected on neurological examination. Laboratory work-up revealed raised blood urea at 118.4mg/dl (normal = 15–40mg/dl) and serum creatinine at 3.84mg/dl (normal = 0.6–1.5mg/dl), with normal serum sodium and potassium. Arterial blood gas showed a high anion gap metabolic acidosis, with pH of 7.08 (normal = 7.35–7.45). T2 and FLAIR sequences of brain MRI revealed near-complete lentiform fork sign bilaterally along with hyperintensities involving bilateral thalamus, midbrain, pons, and left cerebellum (Fig. A, B). A diagnosis of acute renal failure with uremic encephalopathy and systemic infection was considered. With hemodialysis and supportive treatment, the patient improved over the next 10 days. The second patient, a 20-year-old male, presented with fever, vomiting, and breathlessness for 1 week and altered sensorium for 2 days. The patient was in stupor during neurological assessment, but lacked any focal neurological deficit. Laboratory evaluation revealed a hemoglobin of 7.1g/dl (normal = 13–15g/dl), with elevated blood urea at 295mg/dl, serum creatinine at 9.7mg/dl, and uric acid at 8.6mg/dl (normal = 3.4–7mg/dl). Serum calcium was low, at 3mg/dl (normal = 4.4–5.4mg/dl), with normal serum sodium and potassium. Ultrasound examination of the abdomen showed bilateral small, contracted kidneys. Arterial blood gas revealed a high anion gap metabolic acidosis, with pH of 7.10. T2 and FLAIR sequences of brain MRI showed a partial lentiform fork sign, deficient anteriorly, along with hyperintensities involving adjacent white matter and the right midbrain and pons (Fig. C, D). A diagnosis of acute on chronic renal failure, with uremic encephalopathy and systemic infection was considered. The patient stabilized with hemodialysis and supportive treatment over the subsequent 2 weeks. Lentiform fork sign results from vasogenic edema of the lentiform nuclei.2 The edematous external capsule forms the lateral arm of the fork, with both the external and internal capsule joining to build its stem infero-posteriorly. Edema of the medial lentiform margin forms the medial arm, which breaks into two along the medullary laminae to envelop the globus pallidus.2 Lentiform fork sign has been reported in uremic encephalopathy, methanol and ethylene glycol toxicity, propionic acidemia, pyruvate dehydrogenase deficiency, and mitochondrial disorders.2 Metabolic acidosis, commonly observed in these disorders, appears to be a major contributing factor to the pathogenesis of lentiform fork sign.2 Systemic infection in both our patients might have contributed to the renal failure, metabolic acidosis, and lentiform fork sign. An incomplete lentiform fork sign and associated white matter hyperintensities have often been described and might be related to the nature and duration of the associated metabolic derangement.2 The vasogenic edema might be transient, with normalization of brain MRI reported after clinical and biochemical stabilization.2, 3 Authors acknowledge gratitude to both their patients. N.K. was responsible for the conception, design, and writing the first draft of the manuscript. D.K. was responsible for review and critique. Nothing to report.