Keywords
polymicrogyria - choroidal fissure cyst - seizures - MRI
Introduction
Focal lesions such as granulomas, low-grade neoplasms, vascular lesions, or neuronal
migration disorders can be causative factors in adult-onset seizures.[1] Polymicrogyria (PMG) is an abnormality of fissures and sulcation due to various
insults occurring during cortical development in embryonic life.[2] It may manifest as seizures and usually diagnosed early in life with the help of
magnetic resonance imaging (MRI). Choroid fissure cysts (CFCs) are mostly incidental
findings in brain MRI of general population, but may be of significance in those presenting
with seizures as previous reports have mentioned their association with complex partial
seizures.[3]
[4]
[5]
Case Report
A 20-year-old male patient presented with recurrent headaches and seizures since 6
years of age. He was prescribed an antiepileptic drug by a practitioner near his home
but continued to have seizures. His seizures were preceded by an aura of vertigo with
visual disturbances in both eyes followed by eye deviation, neck turning to left side,
oral automatisms, impaired awareness of the episode, and bimanual posturing. But there
was no loss of posture or bilateral spread during event. There was history of nocturnal
events and sudden on-and-off events. No post ictal phenomenon or memory was present
for the event. There was history of unresponsiveness and behavioral arrest during
the event. The last episode was a day prior to presentation to the hospital. His intellectual
and behavioral features were normal. Systemic examination was normal. Electroencephalogram
revealed abnormal interictal epileptiform discharges in right posterior leads, with
generalized slow wave discharges. He was diagnosed to have focal nonmotor onset sensory
(visual) seizures with impaired awareness and was referred for imaging. Plain computed
tomography brain revealed fluid-density lesion lateral to midbrain in the right choroid
fissure region. MRI of the brain (plain and contrast) was performed. A well-defined
lobulated cerebrospinal fluid (CSF) intensity lesion ([Fig. 1]) was seen medial to mediotemporal lobe on right side. There was a mass effect in
the form of compression with associated partial inversion of hippocampus. Mild prominence
of the temporal horn of ipsilateral lateral ventricle was noted with lateral displacement
of choroid plexus. There was no diffusion restriction or contrast enhancement suggesting
CFC. Multiple small gyri and sulci are noted in ipsilateral temporo-occipital lobe
with normal signal as compared with rest of the brain parenchyma suggesting PMG ([Fig. 2]).
Fig. 1 Magnetic resonance imaging (MRI) fluid-attenuated inversion recovery (FLAIR) axial
(A), T2 coronal (B), oblique T2 and T1 inversion recovery (IR) (C and D) coronal, heavily T2-weighted axial SPACE (sampling perfection with application-optimized
contrast using different flip angle evolution) (E), diffusion-weighted image (DWI) (F), ADC (apparent diffusion coefficient) (G), T1 sagittal (H), post-contrast T1 sagittal (I), and axial (J) images showing cerebrospinal fluid (CSF)-like fluid-density lesion (arrows) in the
region of right choroidal fissure without any diffusion restriction.
Fig. 2 Magnetic resonance imaging (MRI) T1 inversion recovery (IR) oblique coronal (A), T2 coronal (B), and T1 sagittal (C) showing multiple small gyri and altered gray–white pattern of polymicrogyria.
Discussion
Routine neuroimaging is recommended for all patients having seizures, particularly
those in adult-onset and with focal type of seizures, at least once, usually before
starting antiepileptic therapy. The likelihood of underlying lesions is more in those
with refractory seizures and may benefit from MR neuroimaging to delineate lesion
for management and if necessary, by surgical planning.[6] PMG is a neuronal developmental disorder characterized by presence of multiple small
partly fused gyri and sulci, and irregularly appearing cortical surface as suggested
by its name. It is due to abnormal cortical formation resulting from disturbance in
cortical development late in the neuronal migration stage or early in the cortical
organization stage.[2] Causes are multifactorial ranging from prenatal infection, ischemia, or exposure
to toxins, to chromosomal abnormalities. The common patterns of PMG are perisylvian
(61%) with parasagittal parieto-occipital accounting for 3%, and there is association
with periventricular gray matter heterotopias in 11%. In perisylvian PMG, 85% are
bilateral and are symmetrical.[7] The median age at presentation noted in the former study is 4 months. Nearly more
than one-third (38%) of cases were diagnosed in either antenatal or neonatal period.
Seizures are the most common clinical sequelae of PMG with approximately 80% of patients
eventually developing seizures and majority within the first 5 years.[7] Other symptoms can be encountered depending on the area of the brain involved. Bilateral
abnormalities may show various syndromic associations. On MRI, the diagnostic criteria
for PMG include unusually thickened and over-folded gray matter, cortical surface
irregularity, and “stippling” or irregularity at gray–white matter interface.[7] It appears as multiple cortical convolutions and shallow sulci with thickened or
normal cortex. An anomalous vein may occasionally be seen in the region of PMG. MRI
is the imaging technique of choice for diagnosing PMG.[8] The management of PMG constitutes antiepileptic drugs and timely follow-up.
Choroid fissure cysts are CSF-like fluid-containing benign cysts that may be congenital
in origin. The CFC can be of arachnoid or neuroepithelial origin, differentiated only
at pathology.[9] However, most are not confirmed with histopathology as they do not require surgery.
There are reports of association of CFC with seizures, attention-deficit hyperactivity
disorder, migraine, and narcolepsy.[3]
[4]
[5]
[10]
[11] Choroid fissure is a C-shaped cleft formed by invagination of choroid plexus into
the ventricle between the thalamus and fornix during the embryonal life. Tela choroidea
and tela fimbria are, respectively, the attachments of villous choroid plexus to thalamus
and fornix at the level of temporal horn of lateral ventricles. The fimbria and the
choroid plexus are a barrier between choroidal fissure and temporal horn of lateral
ventricle.[12]
[13] This landmark is important, as in the case of arachnoid origin, choroid plexus is
displaced laterally from choroidal fissure, and medially displaced if it is of neuroepithelial
(ventricular) origin. At MRI CFCs are typically well-defined unilocular, smoothly
marginated CSF-like fluid-containing cysts exerting mass effect on the adjacent structures.
They do not show contrast enhancement or adjacent edema or gliosis. CFCs are found
incidentally, and the treatment is conservative with interval follow-up, if necessary.[9] If the lesion is large and symptomatic, then surgical treatment includes cyst fenestration
or cystoperitoneal shunting.[13]
Usually, the patients of cortical malformations clinically manifest at a much younger
age. Our case report emphasizes the importance of looking for more subtle abnormalities
such as PMG even in the presence of an obvious lesion of CFC while evaluating an adult
patient presenting with seizure for the first time without any history of trauma or
headache. Subtle changes of PMG can be missed when associated with a cystic lesion
as the cyst itself can have cortex-deforming mass effect as noted in our case. There
have been no reported cases showing coexistence of CFC and PMG. The importance of
this coexistence lies in treatment decisions as both conditions are associated with
seizures. Seizures if associated with only CFCs may resolve with decompression or
fenestration of the cyst or shunting. The presence of associated PMG may warrant long-term
treatment with antiepileptic drugs if surgical resection is not feasible. In our patient,
the patient's seizures were under control with an antiepileptic drug. This case highlights
the dilemma as and when if seizures become refractory in such a patient with dual
pathology. The neurosurgery opinion is to perform a decompression or excision of the
cyst first, if seizures become refractory, and then to look for control of seizures
with medical therapy. The patient is being followed up on an outpatient basis.
