Polymicrogyria

Polymicrogyria

Small gyri with shallow sulci.

Epidemiology

The prevalence of isolated polymicrogyria is unknown. Researchers believe that it may be relatively common overall, although the individual forms of the disorder (such as bilateral generalized polymicrogyria) are probably rare.

Classification

The mildest form is known as unilateral focal polymicrogyria. This form of the condition affects a relatively small area on one side of the brain. It may cause minor neurological problems, such as mild seizures that can be easily controlled with medication. Some people with unilateral focal polymicrogyria do not have any problems associated with the condition.

Bilateral forms of polymicrogyria tend to cause more severe neurological problems. Signs and symptoms of these conditions can include recurrent seizures (epilepsy), delayed development, crossed eyes, problems with speech and swallowing, and muscle weakness or paralysis. The most severe form of the disorder, bilateral generalized polymicrogyria, affects the entire brain. This condition causes severe intellectual disability, problems with movement, and seizures that are difficult or impossible to control with medication.

Etiology

Gene abnormalities e.g. WDR62 and PIK3R2

Intrauterine cerebral injury, after approximately 20 weeks gestation, e.g. infection such as CMV, or hypoxia-ischemia

Metabolic etiology e.g. peroxisomal disorders.

Isolated polymicrogyria can have different inheritance patterns. Several forms of the condition, including bilateral frontoparietal polymicrogyria (which is associated with mutations in the ADGRG1 gene), have an autosomal recessive pattern of inheritance. In autosomal recessive inheritance, both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Polymicrogyria can also have an autosomal dominant inheritance pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Other forms of polymicrogyria appear to have an X-linked pattern of inheritance. Genes associated with X-linked conditions are located on the X chromosome, which is one of the two sex chromosomes. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

Some people with polymicrogyria have relatives with the disorder, while other affected individuals have no family history of the condition. When an individual is the only affected person in his or her family, it can be difficult to determine the cause and possible inheritance pattern of the disorder.


Proteins anchored to the cell surface via glycosylphosphatidylinositol (GPI) play various key roles in the human body, particularly in development and neurogenesis. As such, many developmental disorders are caused by mutations in genes involved in the GPI biosynthesis and remodeling pathway.

Murakami et al. described ten unrelated families with biallelic mutations in PIGB, a gene that encodes phosphatidylinositol glycan class B, which transfers the third mannose to the GPI. Ten different PIGB variants were found in these individuals. Flow cytometric analysis of blood cells and fibroblasts from the affected individuals showed decreased cell surface presence of GPI-anchored proteins. Most of the affected individuals have global developmental and/or intellectual delay, all had seizures, two had polymicrogyria, and four had peripheral neuropathy. Eight children passed away before four years old. Two of them had a clinical diagnosis of DOORS syndrome (deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures), a condition that includes sensorineural deafness, shortened terminal phalanges with small finger and toenails, intellectual disability, and seizures; this condition overlaps with the severe phenotypes associated with inherited GPI deficiency. Most individuals tested showed elevated alkaline phosphatase, which is a characteristic of the inherited GPI deficiency but not DOORS syndrome. It is notable that two severely affected individuals showed 2-oxoglutaric aciduria, which can be seen in DOORS syndrome, suggesting that severe cases of inherited GPI deficiency and DOORS syndrome might share some molecular pathway disruptions 1).

Associations

Polymicrogyria most often occurs as an isolated feature, although it can occur with other brain abnormalities. It is also a feature of several genetic syndromes characterized by intellectual disability and multiple birth defects. These include 22q11.2 deletion syndrome, Adams-Oliver syndromeAicardi syndromeGalloway-Mowat syndromeJoubert syndromeZellweger syndrome.

Megalencephaly-capillary malformation syndrome (MCAP).

Schizencephaly.

Diagnosis

May be difficult to diagnose by CT/MRI, and may be confused with pachygyria.

Treatment

Polymicrogyria (PMG), although the most common brain malformation, represents a low percentage among patients operated on for epilepsy. In cases of hemispheric PMG, electrical status epilepticus during slow sleep (ESESS) may occur leading to an aggravation of the neurological condition and risk of drug resistance. In such cases, surgical treatment can be offered.

Case series

From a population of 230 children who underwent hemispherotomy for epilepsy in the Rothschild Foundation Hospital Fohlen et al. retrospectively reviewed the patients with unilateral PMG and drug-resistant electrical status epilepticus during slow sleep (ESESS) focusing on clinical charts, electrophysiological data, and post-surgical outcome.

Eighteen patients were operated on at a mean age of 7.2 years. The average age was 2 years at seizure onset and 4.4 years at diagnosis of ESESS. All the patients preoperatively had some degree of developmental delay associated with hemiparesis. During ESESS all of them evidenced a cognitive decline and eight experienced a worsening of the hemiparesis; ESESS was resistant to at least three antiepileptic drugs. The outcome of epilepsy, with a mean follow-up of 12.8 years showed that ESESS disappeared in all patients while 16 of 18 became seizure-free. Improvement of behavior and cognitive condition was observed in all.

Hemispherotomy can be helpful in patients with drug-resistant ESESS and hemispheric PMG while keeping in mind that more often an accurate medical treatment can be sufficient. The main benefit of surgery is to definitively stop the seizures and to withdraw the medical treatment while keeping in mind the risk of motor aggravation 2).

References

1)

Murakami Y, Nguyen TTM, Baratang N, Raju PK, Knaus A, Ellard S, Jones G, Lace B, Rousseau J, Ajeawung NF, Kamei A, Minase G, Akasaka M, Araya N, Koshimizu E, van den Ende J, Erger F, Altmüller J, Krumina Z, Strautmanis J, Inashkina I, Stavusis J, El-Gharbawy A, Sebastian J, Puri RD, Kulshrestha S, Verma IC, Maier EM, Haack TB, Israni A, Baptista J, Gunning A, Rosenfeld JA, Liu P, Joosten M, Rocha ME, Hashem MO, Aldhalaan HM, Alkuraya FS, Miyatake S, Matsumoto N, Krawitz PM, Rossignol E, Kinoshita T, Campeau PM. Mutations in PIGB Cause an Inherited GPI Biosynthesis Defect with an Axonal Neuropathy and Metabolic Abnormality in Severe Cases. Am J Hum Genet. 2019 Aug 1;105(2):384-394. doi: 10.1016/j.ajhg.2019.05.019. Epub 2019 Jun 27. PubMed PMID: 31256876.
2)

Fohlen M, Dorfmüller G, Ferrand-Sorbets S, Dorison N, Chipaux M, Taussig D. Parasagittal hemispherotomy in hemispheric polymicrogyria with electrical status epilepticus during slow sleep: Indications, results and follow-up. Seizure. 2019 Jul 23;71:190-200. doi: 10.1016/j.seizure.2019.07.017. [Epub ahead of print] PubMed PMID: 31386962.

Subdural Grid Electrode

Subdural Grid Electrode

Indications

A useful technique for intra-operative functional mapping, for the surgical treatment of epilepsy.

○ Grids are frequently used for extra-operative functional mapping(helpful in children or in the mentally retarded). Subdural grid electrodes are placed with a craniotomy.

○ Surface strip electrodes may be placed through a burr hole.


https://adtechmedical.com/subdural-electrodes

Placement

Traditionally, for subdural grid electrode placement, large craniotomies have been applied for optimal electrode placement. Nowadays, microneurosurgeons prefer patient-tailored minimally invasive approaches. Absolute figures on craniotomy size have never been reported. To elucidate the craniotomy size necessary for successful diagnostics, Schneider et al. reviewed there single-center experience in the Charité.

Within 3 years, 58 patients with focal epilepsies underwent subdural grid implantation using patient-tailored navigation-based craniotomies. Craniotomy sizes were measured retrospectively. The number of electrodes and the feasibility of the resection were evaluated. Sixteen historical patients served as controls.

In all 58 patients, subdural electrodes were implanted as planned through tailored craniotomies. The mean craniotomy size was 28 ± 15 cm2 via which 55 ± 16 electrodes were implanted. In temporal lobe diagnostics, even smaller craniotomies were applied (21 ± 11 cm2). Craniotomies were significantly smaller than in historical controls (65 ± 23 cm2, p < 0.05), while the mean number of electrodes was comparable. The mean operation time was shorter and complications were reduced in tailored craniotomies.

Craniotomy size for subdural electrode implantation is controversial. Some surgeons favor large craniotomies, while others strive for minimally invasive approaches. For the first time, they measured the actual craniotomy size for subdural grid electrode implantation. All procedures were straightforward. They therefore advocate for patient-tailored minimally invasive approaches – standard in modern microneurosurgery – in epilepsy surgery as well 1).


Subdural strip and grid electrode (SDE) implantations have long been used as the mainstay of intracranial seizure localization in the United States. Stereoelectroencephalography (SEEG) is an alternative approach in which depth electrodes are placed through percutaneous drill holes to stereotactically defined coordinates in the brain. Long used in certain centers in Europe, SEEG is gaining wider popularity in North America, bolstered by the advent of stereotactic robotic assistance and mounting evidence of safety, without the need for catheter-based angiography. Rates of clinically significant hemorrhage, infection, and other complications appear lower with SEEG than with SDE implants. SEEG also avoids unnecessary craniotomies when seizures are localized to unresectable eloquent cortex, found to be multifocal or nonfocal, or ultimately treated with stereotactic procedures such as laser interstitial thermal therapy (LITT), radiofrequency thermocoagulation (RF-TC), responsive neurostimulation(RNS), or deep brain stimulation (DBS). While SDE allows for excellent localization and functional mapping on the cortical surface, SEEG offers a less invasive option for sampling disparate brain areas, bilateral investigations, and deep or medial targets. SEEG has shown efficacy for seizure localization in the temporal lobe, the insula, lesional and nonlesional extra-temporal epilepsy, hypothalamic hamartomas, nodular periventricular heterotopias, and patients who have had prior craniotomies for resections or grids. SEEG offers a valuable opportunity for cognitive neurophysiology research and may have an important role in the study of dysfunctional networks in psychiatric disease and understanding the effects of neuromodulation 2).

Case series

Hamer et al retrospectively reviewed the records of all patients who underwent invasive monitoring with subdural grid electrodes (n = 198 monitoring sessions on 187 patients; median age: 24 years; range: 1 to 50 years) at the Cleveland Clinic Foundation from 1980 to 1997.

From 1980 to 1997, the complication rate decreased (p = 0.003). In the last 5 years, 19/99 patients (19%) had complications, including two patients (2%) with permanent sequelae. In the last 3 years, the complication rate was 13.5% (n = 5/37) without permanent deficits. Overall, complications occurred during 52 monitoring sessions (26.3%): infection (n = 24; 12.1%), transient neurologic deficit (n = 22; 11.1%), epidural hematoma (n = 5; 2.5%), increased intracranial pressure (n = 5; 2.5%), and infarction (n = 3; 1.5%). One patient (0.5%) died during grid insertion. Complication occurrence was associated with greater number of grids/electrodes (p = 0.021/p = 0.052; especially >60 electrodes), longer duration of monitoring (p = 0.004; especially >10 days), older age of the patient (p = 0.005), left-sided grid insertion (p = 0.01), and burr holes in addition to the craniotomy (p = 0.022). No association with complications was found for number of seizures, IQ, anticonvulsants, or grid localization.

Invasive monitoring with grid electrodes was associated with significant complications. Most of them were transient. Increased complication rates were related to left-sided grid insertion and longer monitoring with a greater number of electrodes (especially more than 60 electrodes). Improvements in grid technology, surgical technique, and postoperative care resulted in significant reductions in the complication rate 3).


From 1987 to 1992, invasive EEG studies using subdural strips, subdural grids or depth electrodes were performed in a total of 160 patients with medically intractable epilepsy, in whom scalp EEG was insufficient to localize the epileptogenic focus. Dependent on the individual requirements, these different electrode types were used alone or in combination. Multiple strip electrodes with 4 to 16 contacts were implanted in 157 cases through burrholes, grids with up to 64 contacts in 15 cases via boneflaps, and intrahippocampal depth electrodes in 36 cases using stereotactic procedures. In every case, localization of the electrodes with respect to brain structures was controlled by CT scan and MRI. Visual and computerized analysis of extra-operative recordings allowed the localization of a resectable epileptogenic focus in 143 patients (89%), who subsequently were referred for surgery, whereas surgery had to be denied to 17 patients (11%). We did not encounter any permanent morbidity or mortality in our series. In our experience, EEG-monitoring with chronically implanted electrodes is a feasible technique which contributes essentially to the exact localization of the epileptogenic focus, since it allows nearly artefact-free recording of the ictal and interictal activity. Moreover, grid electrodes can be used for extra-operative functional topographic mapping of eloquent brain areas 4).

References

1)

Schneider UC, Oltmanns F, Vajkoczy P, Holtkamp M, Dehnicke C. Craniotomy Size for Subdural Grid Electrode Placement in Invasive Epilepsy Diagnostics. Stereotact Funct Neurosurg. 2019 Jul 30:1-9. doi: 10.1159/000501235. [Epub ahead of print] PubMed PMID: 31362296.
2)

Youngerman BE, Khan FA, McKhann GM. Stereoelectroencephalography in epilepsy, cognitive neurophysiology, and psychiatric disease: safety, efficacy, and place in therapy. Neuropsychiatr Dis Treat. 2019 Jun 28;15:1701-1716. doi: 10.2147/NDT.S177804. eCollection 2019. Review. PubMed PMID: 31303757; PubMed Central PMCID: PMC6610288.
3)

Hamer HM, Morris HH, Mascha EJ, Karafa MT, Bingaman WE, Bej MD, Burgess RC, Dinner DS, Foldvary NR, Hahn JF, Kotagal P, Najm I, Wyllie E, Lüders HO. Complications of invasive video-EEG monitoring with subdural grid electrodes. Neurology. 2002 Jan 8;58(1):97-103. PubMed PMID: 11781412.
4)

Behrens E, Zentner J, van Roost D, Hufnagel A, Elger CE, Schramm J. Subdural and depth electrodes in the presurgical evaluation of epilepsy. Acta Neurochir (Wien). 1994;128(1-4):84-7. PubMed PMID: 7847148.

Anterior temporal lobectomy complications

Anterior temporal lobectomy complications

Even though the mortality after Anterior temporal lobectomy (ATL) is minimal, the overall morbidity cannot be ignored. Psychiatric disturbances, visual field defects, and cognitive disorders are the most common postoperative complications, and should be considered during the preoperative planning and consultation 1).

Visual field defects

ATL is often complicated by quadrantanopia. In some cases this can be severe enough to prohibit driving, even if a patient is free of seizures. These deficits are caused by damage to Meyers loop of the optic radiation, which shows considerable heterogeneity in its anterior extent. This structure cannot be distinguished using clinical magnetic resonance imaging sequences.

Optic radiation tractography by DTI could be a useful method to assess an individual patient’s risk of postoperative visual deficit 2)3).

van Lanen et al., developed a score method for the assessment of postoperative visual field defects after temporal lobe epilepsy surgery and assessed its feasibility for clinical use. A significant correlation between VFD and resection size for right-sided ATL was confirmed 4).

Cranial nerve (CN) deficits following anterior temporal lobectomy (ATL) are an uncommon but well-recognized complication. The usual CNs implicated in post-ATL complications include the oculomotor nervetrochlear nerve, and facial nerves.

Injury to the trigeminal nerve leading to neuropathic pain are described in 2 cases following temporal lobe resections for pharmacoresistant epilepsy. The possible pathophysiological mechanisms are discussed and the microsurgical anatomy of surgically relevant structures is reviewed. 5).

Case reports

Dickerson et al., from the Department of Neurosurgery, University of Mississippi Medical Center, JacksonUSA report the third known case and first of diffuse vasospasm. A 48-year-old woman underwent a transcortical anterior left temporal lobectomy. Eleven days later, she had new-onset expressive aphasia with narrowing of the anterior, middle, and posterior cerebral arteries, and increased velocities via transcranial Doppler. She was treated with fluids, nimodipine, and permissive hypertension. At 6 months, her speech was near baseline. Cerebral vasospasm may represent a rare cause of morbidity after anterior temporal lobectomy; a literature review on the subject is presented 6).

References

1)

Brotis AG, Giannis T, Kapsalaki E, Dardiotis E, Fountas KN. Complications after Anterior Temporal Lobectomy for Medically Intractable Epilepsy: A Systematic Review and Meta-Analysis. Stereotact Funct Neurosurg. 2019 Jul 9:1-14. doi: 10.1159/000500136. [Epub ahead of print] Review. PubMed PMID: 31288240.
2)

Borius PY, Roux FE, Valton L, Sol JC, Lotterie JA, Berry I. Can DTI fiber tracking of the optic radiations predict visual deficit after surgery? Clin Neurol Neurosurg. 2014 Jul;122:87-91. doi: 10.1016/j.clineuro.2014.04.017. Epub 2014 May 5. PubMed PMID: 24908224.
3)

James JS, Radhakrishnan A, Thomas B, Madhusoodanan M, Kesavadas C, Abraham M, Menon R, Rathore C, Vilanilam G. Diffusion tensor imaging tractography of Meyer’s loop in planning resective surgery for drug-resistant temporal lobe epilepsy. Epilepsy Res. 2015 Feb;110:95-104. doi: 10.1016/j.eplepsyres.2014.11.020. Epub 2014 Nov 27. PubMed PMID: 25616461.
4)

van Lanen RHGJ, Hoeberigs MC, Bauer NJC, Haeren RHL, Hoogland G, Colon A, Piersma C, Dings JTA, Schijns OEMG. Visual field deficits after epilepsy surgery: a new quantitative scoring method. Acta Neurochir (Wien). 2018 Jul;160(7):1325-1336. doi: 10.1007/s00701-018-3525-9. Epub 2018 Apr 5. PubMed PMID: 29623432; PubMed Central PMCID: PMC5995984.
5)

Gill I, Parrent AG, Steven DA. Trigeminal neuropathic pain as a complication of anterior temporal lobectomy: report of 2 cases. J Neurosurg. 2016 Apr;124(4):962-5. doi: 10.3171/2015.5.JNS15123. Epub 2015 Oct 30. PubMed PMID: 26517768.
6)

Dickerson JC, Hidalgo JA, Smalley ZS, Shiflett JM. Diffuse vasospasm after transcortical temporal lobectomy for intractable epilepsy. Acta Neurochir (Wien). 2018 Jul 10. doi: 10.1007/s00701-018-3606-9. [Epub ahead of print] PubMed PMID: 29987392.
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