Understanding the Occipital lobe part2(Neuroscience)
- Intralobar fibres of the occipital lobe: a post mortem dissection study(PubMed)
Author : Francesco Vergani 1, Sajedha Mahmood 2, Cristopher M Morris 3, Patrick Mitchell 4, Stephanie J Forkel 5
Abstract : Introduction: The atlas by Heinrich Sachs (1892) provided an accurate description of the intralobar fibres of the occipital lobe, with a detailed representation of the short associative tracts connecting different parts of the lobe. Little attention has been paid to the work of Sachs since its publication. In this study, we present the results of the dissection of three hemispheres, performed according to the Klingler technique (1935). Our anatomical findings are then compared to the original description of the occipital fibres anatomy as detailed by Sachs.
Methods: Three hemispheres were dissected according to Klingler’s technique (1935). Specimens were fixed in 10% formalin and frozen at -15 °C for two weeks. After defreezing, dissection of the white matter fibres was performed with blunt dissectors. Coronal sections were obtained according to the cuts originally described by Sachs. In addition, medial to lateral and lateral to medial dissection of the white matter of the occipital lobe was also performed.
Results: A network of short association fibres was demonstrated in the occipital lobe, comprising intralobar association fibres and U-shaped fibres, which are connecting neighbouring gyri. Lateral to the ventricles, longitudinal fibres of the stratum sagittale were also identified that are arranged as external and internal layers. Fibres of the forceps major were also found to be in direct contact with the ventricular walls. We were able to replicate all tracts originally described by Sachs. In addition, a previously unrecognised tract, connecting the cuneus to the lingual gyrus, was identified. This tract corresponds to the “sledge runner”, described in tractography studies.
Conclusions: The occipital lobe shows a rich network of intralobar fibres, arranged around the ventricular wall. Good concordance was observed between the Klingler dissection technique and the histological preparations of Sachs.
2.Surgical outcome in occipital lobe epilepsy: implications for pathophysiology (PubMed)
Author : C Aykut-Bingol 1, R A Bronen, J H Kim, D D Spencer, S S Spencer
Abstract : Medically refractory occipital lobe epilepsies are increasingly treated with surgery, but outcome and its relationship to etiology, pathological substrate, occipital lobe location, surgical approach, and electroclinical features have not been systematically investigated in a substantial group of patients. Thirty-five patients who underwent surgery for intractable occipital lobe seizures were retrospectively evaluated. Outcome and occipital lobe location were analyzed with respect to surgical procedure, pathology, clinical seizure characteristics, seizure onset and termination locations, and localization of interictal spikes. Most patients had developmental abnormalities (14) or tumors (13, all gliomas). Developmental abnormalities consisted of focal cortical dysplasia (5), heterotopia (2), hamartoma (3), cortical duplication (1), polymicrogyria (1), Sturge-Weber syndrome (1), and tuberous sclerosis (1). There was 1 patient with a vascular abnormality, 1 with chronic inflammatory changes, 4 with gliosis, 1 with cerebral ossification, and 1 with normal pathology. Developmental abnormalities had significantly worse outcome (45% excellent/good) than tumors (85% excellent/good). In the developmental group, low-grade focal cortical dysplasias had better outcome than heterotopia and hamartoma regardless of type of surgical procedure. Pathological groups did not significantly differ with respect to location within the occipital lobe (overall medial [50%] or lateral [38%]); clinical seizure characteristics referable to specific lobe (occipital [14%], temporal [34%], frontal [23%], more than one type [29%]); electroencephalographic localization (to occipital [17%], temporal [27%], or other/multifocal locations [56%]); or intracranial ictal onset or termination location. Electroclinical variables were also unrelated to the occipital lobe location of abnormality. Surgical outcome was not predicted by surgical approach (lesion excision with margins or lobectomy). The main pathological substrates of uncontrolled occipital lobe epilepsy are gliomas and developmental abnormalities. Whereas resection of occipital lobe tumors associated with chronic epilepsy produces nearly uniform seizure control, outcome after resection of occipital lobe developmental abnormalities is less uniform.
