An unusual case of unilateral frontal presylvian polymicrogyria with periventricular heterotopia.

Clinical History

A 50-year-old patient presented to A&E with tonic-clonic seizure for the first time, lasting a few seconds, followed by post-ictal agitation and confusion for approximately 10 min. No past medical history of note. Neurological and other systemic examinations were unremarkable. Routine bloods were all within normal range.

Imaging Findings

The patient underwent MRI head with contrast (Figure 1), which revealed asymmetry of the frontal lobes, the left frontal lobe being smaller and showing irregular outline with multiple overlying sulci. The left frontal lobe demonstrated abnormal crowded numerous small gyri containing abnormally high T2/FLAIR white matter signal in-between. The lesion was effacing the left frontal horn of the lateral ventricle and causing small subfalcine herniation. There was also evidence of similar change in the left caudate head. A small ipsilateral closed lip schezincephalic defect in the frontal horn of the lateral ventricle was also demonstrated. There was also diffuse white matter disease in the form of multiple small high signal foci, compatible with enhanced perivascular spaces. No evidence of haemorrhage, acute infarction or oedema was noted. Skull base and sinuses were unremarkable.

Discussion

Polymicrogyria (PMG) as the name suggests is a disease characterised by excessive small partly fused gyri. It is thought to be a disease of cortical malformation arising due to disturbance in cortical development late in the neuronal migration stage or early in the cortical organisation stage [1].

According to Leventar et al., the most common pattern of PMG was presylvian (61%) of which 85% were bilateral and the majority were symmetrical. In terms of the age at presentation, median age at presentation was 4 months with 38% presenting in either antenatal or neonatal period. The most common clinical sequelae was seizures. Our patient therefore fits the most common subtype of PMG with overlying PNH and presented with the most common clinical sequelae i.e. seizure [2].

The above study defined an MRI-based criteria to diagnose PMG. According to this, the diagnosis of PMG would be highly suggestive if the MRI shows (i) Irregular cortical surface (ii) Thickened or over-folded cortex (iii) ‘Stippling’ or irregularity at the interface of grey and white matter [2].

Heterotopias are a group of disorders arising from abnormally positioned neurons. Heterotopias can be macroscopically classified into two broad groups (i) Nodular and (ii) Diffuse. Periventricular or Subependymal heterotopia, a sub-type of nodular heterotopia (PNH), is by far the commonest type [3].

The severity and diversity of clinical presentation depends on the extent and anatomical location of PNH. Again, the most common clinical sequelae of PNH is seizures [4]. Median age at onset of seizure in patients with simple PNH is 19.2 years (for more extensive PNH this is much earlier (4.25 years) [5]. As with PMG, MRI head with contrast is the gold-standard in the diagnosis of PNH [6-8].

The case was discussed with the neurosurgical team. They advised starting the patient on Levetiracetam and Dexamethasone. The patient was seen by the on-call neurologist who agreed with the diagnosis and advised discharging the patient if seizure free for 24 hours on anti-epileptic medication. The patient has not had any further seizure and is currently stable, with normal social functioning and under regular follow up by a neurologist.

Hence, MRI remains a gold-standard imaging modality in diagnosing PMG/PNH, and although clinical manifestations of cortical malformations usually presents at a much younger age, this case report emphasises the importance of keeping the above diagnoses in mind if an adult presents with seizure for the first time without any history of trauma or headache.

Differential Diagnosis List

Final Diagnosis

MRI findings were suggestive of long standing left frontal PMG+PNH

URL:	https://www.eurorad.org/case/14281
DOI:	10.1594/EURORAD/CASE.14281
ISSN:	1563-4086