Tumefactive demyelinating lesion

Case contributed by Khaloud Alghamdi


Previously healthy, presented with isolated right-sided facial sensory loss.

Patient Data

Age: 55 years
Gender: Female

A space occupying lesion is present in the right middle cerebellar peduncle, involving the
anterior aspect of the right cerebellar hemisphere with extension to ipsilateral pons; it measures 3.3 cm AP x 2.8 cm transverse. The mass appears hypointense on T1 and hyperintense signal change on T2 and FLAIR. It is causing an expansion of the middle cerebellar peduncle, with minimal mass effect on the fourth ventricle. It involves the course of the right trigeminal nerve.

Post-contrast, there is heterogeneous, incomplete peripheral enhancement of the mass.
There is no significant increase in rCBV ratio in perfusion images in the periphery or adjacent region.

The differential diagnosis at this point included: high grade glioma, lymphoma or tumefactive demyelinating lesion.

A biopsy-proven diagnosis was deferred considering risks outweighing benefits which were non-negligible.  To increase the diagnostic accuracy in distinguishing a malignant process from a TDL in this case, a non-enhanced CT scan was carried on the next day.

The enhancing portion of a malignant lesion would appear dense on CT (high cellularity). While a demyelinating lesion would appear homogeneously hypodense (decreased cellularity and edema).

Most of the peripheral enhancing components of the right middle cerebellar peduncle lesion are obscured by artifact on CT scan. However, an enhancing component in the right lateral aspect of the pons (on MRI) is well visualized on CT and demonstrates relatively low density. This has been reported in the literature to favor tumefactive demyelination over a glioma or lymphoma.

Case Discussion

The patient was started on steroid therapy. Follow up MRI of the patient shows a minimal decrease in the size and enhancement of the lesion with interval development of a couple of supratentorial juxtacortical lesions, favoring demyelinating process over a tumor.

Beware of false-negative CT scan, as 30% of PCNSL can appear diffusely hypointense, this should be correlated with other MRI findings, lumbar puncture results +/- FDG PET.

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