Letter: Seizure Outcomes in Occipital Lobe and Posterior Quadrant Epilepsy Surgery: A Systematic Review and Meta-Analysis : Neurosurgery

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Letter: Seizure Outcomes in Occipital Lobe and Posterior Quadrant Epilepsy Surgery: A Systematic Review and Meta-Analysis

Cossu, Giulia MD; Messerer, Mahmoud MD, MSc; Daniel, Roy Thomas MBBS, MCh

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Neurosurgery 84(6):p E448, June 2019. | DOI: 10.1093/neuros/nyz065

To the Editor:

We wish to commend Harward et al1 for their excellent paper dealing with seizure outcome in occipital lobe and posterior quadrant epilepsy surgery.

Occipital lobe epilepsy is a relatively rare subgroup of refractory epilepsy. The data on this subject, therefore, remains scarce and this article enables an increase in the knowledge in this field.

Following occipital lobe epilepsy surgery, visual field defects are a significant problem. The authors report 57% of patients with postoperative visual impairment and the visual outcome was not influenced by the seizure outcome.1 In these situations, patient counseling prior to surgery is of considerable importance because the presence of a dense homonymous hemianopia may be as invalidating as refractory seizures. It would have been interesting to analyze if the visual outcome was dependent on the age at seizure onset, as optic fields may develop differently in patients with refractory epilepsy secondary to congenital etiologies compared to healthy children.2 Cortical reorganization may in fact occur with brain development after early childhood or perinatal occipital lobe damage/malformations. This might explain why this specific cohort of patients with early onset occipital lobe lesions rarely complain of visual symptoms and subsequent epilepsy surgery rarely creates new visual deficits. Compensatory mechanisms for hemianopia such as exotropia and anomalous head posture are also more frequently observed in younger children, especially after surgery in the nondominant hemisphere and also with an earlier onset of epilepsy.3 The situation is different in adult-onset epilepsy patients. Visual deficits are more common with lesions affecting the entire occipital lobe or its medial part.4 The resection of the primary visual cortex is associated with visual field defects, while resection of the lateral occipital lobe is associated with peripheral visual loss and vision-specific role difficulties.5 The visual outcome after surgery both for smaller occipital lesions and for larger lesions like posterior quadrant epilepsy is largely dependent on the age at onset of the pathological process. In our opinion, it would have, therefore, been very interesting if the authors had been able to do an analysis on these lines.

Another limitation of this study is that the cohort of patients included both occipital lobe epilepsies and multilobar epileptic lesions (that included the occipital lobe). Of the 27 studies reported, only 14 included patients with an isolated occipital lobe epilepsy and only 56% of patients had a well-defined occipital focus. The absence of a subgroup analysis (lobar vs multilobar) compromises the interpretation of the seizure outcome data and the reported rate of 65% Engel class I in the whole cohort does not reflect clearly the seizure outcome for these 2 subgroups that are distinct.

The type of surgery performed in this meta-analysis was also heterogeneous among studies (as is always the case) and it would have been interesting to analyze if a correlation is present between favorable postoperative outcome and a specific surgical procedure, eg, resective vs disconnective surgery or even if SEEG influenced the seizure outcome. As stressed by the authors, epilepsy surgery for refractory occipital lobe epilepsy represents a valid option and further studies dealing solely with OLE patients without including posterior quadrant epileptogenic foci, would be very contributive in establishing the real prognosis of these patients.

Disclosure

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

REFERENCES

1. Harward SC, Chen WC, Rolston JD, Haglund MM, Englot DJ. Seizure outcomes in occipital lobe and posterior quadrant epilepsy surgery: a systematic review and meta-analysis. Neurosurgery. 2018;82(3):350-358.
2. Taylor I, Scheffer IE, Berkovic SF. Occipital epilepsies: identification of specific and newly recognized syndromes. Brain: J Neurol. 2003;126(4):753-769.
3. Koenraads Y, van der Linden DC, van Schooneveld MM, et al. Visual function and compensatory mechanisms for hemianopia after hemispherectomy in children. Epilepsia. 2014;55(6):909-917.
4. Yang PF, Jia YZ, Lin Q, et al. Intractable occipital lobe epilepsy: clinical characteristics, surgical treatment, and a systematic review of the literature. Acta Neurochir. 2015;157(1):63-75.
5. Heo W, Kim JS, Chung CK, Lee SK. Relationship between cortical resection and visual function after occipital lobe epilepsy surgery. J Neurosurg. 2018;129(2):524-532.
Copyright © 2019 by the Congress of Neurological Surgeons