Gadolinium enhancement in brain magnetic resonance imaging in progressive multifocal leukoencephalopathy after natalizumab monotherapy: is it really atypical?

Progressive multifocal leukoencephalopathy (PML) generally occurs in patients with impaired cellular immunity. Monoclonal antibodies also predispose the patient to PML as they depress the immune system. PML was classically characterized by a lack of inflammation and absence of gadolinium enhancement. However, gadolinium enhancement of PML lesions was first described in HIV-positive patients under therapy. We present a case of gadolinium enhanced PML lesions occuring after natalizumab monotherapy of a relapsing multiple sclerosis. Radiologists must be aware of this particular feature, as confirmation of the diagnostic of PML becomes more challenging. Namely, distinction between starting PML and multiple sclerosis enhanced additional active lesion is difficult and diagnosis must be established by combined analysis of full clinical evolution, brain MRI scans, and polymerase chain reaction of cerebrospinal fluid.

[Intradiploic parietal meningoencephalocele]. / Méningoencéphalocèle intradiploïque pariétale.

Intradiploic meningoencephalocele is rarely found in adulthood. It is thought to be postraumatic and must be differenciated from congenital encephalocele. Imaging findings, particularly with Magnetic Resonance Imaging, are useful in determining the various linings and contents of this intradiploic defect.