Transmantle sign (brain)

Last revised by Frank Gaillard on 22 May 2024

The transmantle sign is an MRI feature of focal cortical dysplasia (FCD), almost exclusively seen in type II (ILAE/Blumcke classification), and especially in type IIb 1-5.

The transmantle sign is believed to be related to abnormal function of, or injury to radial glial fibers (which go on to transform into astrocytes) and form the scaffolding over which neurons migrate from the periventricular germinal matrix to the cortex 3. The presence of hypo- or dysmyelination, gliosis, neuronal heterotopia, and balloon cells may all contribute to its appearance 5.

Although CT is not ideal for the identification of the transmantle sign, it can be visualized as a region of abnormal attenuation, usually increased 5. This is thought to be primarily due to the presence of balloon cells, although microcalcification may also play a role 5.

The key feature of the transmantle sign is a funnel-shaped high T2/FLAIR signal extending from the cortex down to the ventricle 1,5. T1 signal is variable. It can be hypo- or hyperintense compared to surrounding white matter. Hyperintensity appears to be correlated with the presence of abundant balloon cells and, therefore, indicative of type IIb focal cortical dysplasia 5.

It is variably associated with other features of focal cortical dysplasia, such as cortical thickening and blurred grey/white junction (see focal cortical dysplasia article).

Presence of a transmantle sign is associated with good post-surgical seizure-free outcomes 1

The main differentials are:

  • radial band sign of tuberous sclerosis

    • very similar in appearance on imaging 6

    • cortical tubers are usually multiple

    • other stigmata of tuberous sclerosis usually visible

    • it remains unclear whether the radial band sign and transmatle sign are actually the same pathology or distinct entities 7,8

  • closed-lip schizencephaly 4

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