Teaching Case

A young patient presented with weakness in the lower limbs and acute onset seizure which was progressive in nature. There was no history of drug intake or any cardiovascular complaint.

A CECT (Fig 1) of the patient presenting with seizure and weakness showed a minimally enhanced lesion with surrounding mild oedema in the right parietal lobe which on post contrast T2WI (Fig 1b) shows a hyperintense area in the right parasagittal location. Post contrast T1WI (Fig 2) shows open ring type peripheral enhancement with smooth walls. MRS (Fig 3) of lesion shows inverted lactate doublet with increased CHO/CR and CHO/NAA. On follow-up CECT ( Fig 4) there was a reduction in size and enhancement of the lesion.

Tumefactive demyelinating lesion (TDL) or monofocal acute inflammatory demyelination is a locally aggressive form of demyelination usually manifesting as a solitary lesion mimicking a neoplasm on imaging. The most common pattern is a nodular pattern of enhancement. Sometimes these lesions may demonstrate a ring-enhancing pattern or other patterns. No imaging features described are specific for acute demyelinating disorders on imaging. The only exception to this is an open ring or incomplete ring lesion. Presence of an open ring or incomplete ring helps in differentiating these lesions from large tumours or infective conditions like brain abscesses. Demyelinating lesions, including both classic multiple sclerosis and tumefactive demyelination, may also create an open ring or incomplete ring sign on post contrast image [1, 2].
The detection and characterization of plaques by CT depends on (1) The difference in attenuation between the focus of demyelination and adjacent normal structures, (2) the size of the plaque in relation to the CT slice thickness, (3) plaque location, (4) plaque age, and (5) the use of iodinated contrast material [2].The lesion appears as an ill-defined ring enhancing lesion with central hypodensity (necrosis), and also shows perilesional oedema and minimal mass effect on CT [3]. On MRI the lesions often tend to be large, however with relatively little mass effect or minimally surrounding oedema. Sometimes centrally located dilated veins are observed within these lesions. On T1 C+ (Gd) up to 50% of tumefactive demyelinating lesions show contrast enhancement; the enhancement pattern is usually in the form on an open ring and the incomplete portion of the ring is on the gray matter side of the lesion [4]. Perfusion imaging is often helpful in differentiating tumefactive demyelinating lesions from high-grade gliomas and lymphomas; mean relative cerebral blood volume of tumefactive demyelinating lesions is less than in tumours [5]. MRS shows increase in CHO, reduced NAA and lactate peak in the lesion. Saindane et al. found no significant differences in mean Cho/Cr ratios in the corresponding contrast-enhancing, central, or perilesional areas of TDLs and gliomas. The mean central-region NAA/Cr ratio in gliomas was significantly lower than in TDLs, but mean NAA/Cr ratios in other regions were not significantly different [6].
Treatment with corticosteroids decreases the degree of contrast enhancement in individual lesions, and can dramatically reduce the total number of contrast enhancing lesions through stabilization of the blood brain barrier.