Teaching Case

A 17-year-old female patient with a known seizure disorder presented to the casualty with tonic-clonic seizures, in an unconscious state, and loss of both upper and lower limb reflexes. She was previously on anti-epileptics, which were stopped for 2 months for a gummatous inflammation.

MRI brain images showed an oval well-defined altered signal intensity lesion on T2-weighted and FLAIR images in the central part of the splenium of the corpus callosum, which showed diffusion restriction and no obvious enhancement on post-contrast images. After the first MRI, phenytoin was started again, after which the patient started gradually regaining consciousness and power in the upper and lower limbs. Serial follow-up MRI scans were performed, which showed that there was a significant reduction in signal intensity in the splenium of the corpus callosum.

Background:
A transient splenial lesion of the corpus callosum is a non-specific finding with multiple aetiologies [5]. Polster et al [1] proposed that in seizure disorder patients, an altered signal intensity lesion can be seen after an episode of status epilepticus or withdrawal of anti-epileptic drugs.

Clinical perspective:
Typically, patients can present with signs and symptoms of hemispheric disconnection such as pseudo-neglect, alien hand syndrome, apraxia of the left hand, agraphia, alexia and visual apraxias [6].

Imaging perspective:
Takanashi et al [2] reported a study of 4 patients with epilepsy, where the altered signal intensities were mostly ovoid or round in shape, in contrast to other callosal lesions like encephalomyelitis and ADEM, which may involve the lateral portions of splenium and white matter. Polster et al [1] suggested that withdrawal of anti-epileptic drugs or an epileptic episode itself causes an imbalance of arginine-vasopressin fluid balance systems, causing vasogenic oedema in the splenium of the corpus callosum. Whereas, Maeda et al [3] hypothesized that it cannot be due to vasogenic oedema, rather a cytotoxic oedema that causes diffusion restriction instead of an increase in signal on ADC images. They postulated that the reduction in signal on ADC images is because of local fluid retention in intracellular compartment after separation of myelin fibres. Prilipko et al [4] tried to test the different hypotheses of pathophysiology given by others of the altered signal by measuring the arginine-vasopressin levels in two epileptic patients in acute phase and found that there is an imbalance of arginine-vasopressin in the active phase of epilepsy. He concluded that the lesion is due to cytotoxic oedema at a glial level as there is no neurological or neurophysiological disruption on DTI.

Outcome :
The neurological recovery of the patients is good, according to the study by Prilipko et al [4]. They stated that the lesion is completely reversible in a month. In our patient, there was an improvement seen clinically and radiologically by a significant reduction in the signal in the splenium of the corpus callosum within 14 days.

Take home message:
Transient splenial lesions of the corpus callosum have a wide range of differential diagnoses, which should be kept in mind before jumping to conclusions and starting treatment. The well-circumscribed oval lesion is mostly seen in an epileptic patient, due to the sudden withdrawal of drugs, especially carbamazepine which is said to cause more increase in the anti-diuretic effect than the other anti-epileptic drugs [1]. Hence, care should be taken while tapering anti-epileptic drugs.