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Focal cortical dysplasia type IIa and IIb: MRI aspects in 118 cases proven by histopathology

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Abstract

Introduction

This study aims to review the magnetic resonance imaging (MRI) aspects of a large series of patients with focal cortical dysplasia type II (FCD II) and attempt to identify distinctive features in the two histopathological subtypes IIa and IIb.

Methods

We retrospectively reviewed the MRI scans of 118 patients with histological proven FCD IIa (n = 37) or IIb (n = 81) who were surgically treated for intractable epilepsy.

Results

MRI was abnormal in 93 patients (79 %) and unremarkable in 25 (21 %). A dysplastic lesion was identified in 90 cases (97 %) and classified as FCD II in 83 and FCD non-II in seven cases. In three cases, the MRI diagnosis was other than FCD. There was a significant association between the presence of cortical thickening (p = 0.002) and the “transmantle sign” (p < 0.001) and a correct MRI diagnosis of FCD II. MRI positivity was more frequent in the patients with FCD IIb than in those with FCD IIa (91 % vs. 51 %), and the detection rate of FCD II was also better in the patients with type IIb (88 % vs. 32 %). The transmantle sign was significantly more frequent in the IIb subgroup (p = 0.003).

Conclusions

The rates of abnormal MRI results and correct MRI diagnoses of FCD II were significantly higher in the IIb subgroup. Although other MRI stigmata may contribute to the diagnosis, the only significant correlation was between the transmantle sign and FCD IIb.

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Acknowledgment

We thank Dr Alessio Moscato, Medical Physics Department, Ospedale Niguarda—Milano, for his assistance in imaging editing.

Conflict of interest

We declare that we have no conflict of interest.

Author information

Authors and Affiliations

  1. Department of Neuroradiology, Ospedale Cà Granda Niguarda, Piazza Ospedale Maggiore 3, 20162, Milano, Italy

    Nadia Colombo

  2. Claudio Munari Epilepsy Surgery Center, Ospedale Niguarda, Milano, Italy

    Laura Tassi, Roberto Mai, Ivana Sartori, Francesco Cardinale & Giorgio Lo Russo

  3. Department of Epilepsy Clinic and Experimental Neurophysiology, IRCCS Foundation Neurological Institute “C. Besta”, Milano, Italy

    Francesco Deleo & Roberto Spreafico

  4. Department of Neuroradiology, Ospedale Cà Granda Niguarda, Milano, Italy

    Alberto Citterio

  5. Department of Pathology, Ospedale Niguarda, Milano, Italy

    Manuela Bramerio

Authors
  1. Nadia Colombo
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  2. Laura Tassi
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  3. Francesco Deleo
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  4. Alberto Citterio
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  5. Manuela Bramerio
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  6. Roberto Mai
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  7. Ivana Sartori
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  8. Francesco Cardinale
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  9. Giorgio Lo Russo
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  10. Roberto Spreafico
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Corresponding author

Correspondence to Nadia Colombo.

Additional information

Key learning points

1 — Focal cortical dysplasia type II (FCD II) are highly epileptogenic lesions that are frequently associated with early-onset drug-resistant partial epilepsy (DRPE).

2 — According to the original description and to the most recent classification systems two histological subgroups of FCD II are recognized: IIa characterized by the presence of abnormal cortical dyslamination and dysmorphic neurons and IIb with additional BCs.

3 — The most frequent MRI features for FCD II include: increased cortical thickness, blurred gray/white matter junction on T1WI, blurred or sharp gray/white matter junction on T2WI, increased signal on T2WI and decreased signal on T1WI of the subcortical white matter and gyration anomalies. The most peculiar feature is the tapering of the WM signal alteration towards the ventricle, the so called “transmantle sign”.

4 — According to the present results, a differential MRI diagnosis between the two histopathological subgroups can be attempted. Abnormal MRI results as well as the peculiar “funnel-shaped” transmantle sign are significantly more frequent in FCD IIb.

5 — The differential MRI diagnosis has a prognostic value owing to a more favourable surgical outcome in FCD IIb.

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Colombo, N., Tassi, L., Deleo, F. et al. Focal cortical dysplasia type IIa and IIb: MRI aspects in 118 cases proven by histopathology. Neuroradiology 54, 1065–1077 (2012). https://doi.org/10.1007/s00234-012-1049-1

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  • DOI: https://doi.org/10.1007/s00234-012-1049-1

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