Comparative anatomy of dissected optic lobes, optic ventricles, midbrain tectum, collicular ventricles, and aqueduct: evolutionary modifications as potential explanation for non-tumoral aqueductal anomalies in humans

Purpose An extensive literature has postulated multiple etiologies for aqueductal stenosis. No publications were found, discussing that evolutionary modifications might explain aqueductal anomalies. This study’s objectives were to review the evolutionary modifications of vertebrates’ tectum structures that might explain human aqueduct anomalies. Undertaking vertebrate comparative study is currently not feasible in view of limitations in obtaining vertebrate material. Thus, vertebrate material collected, injected, dissected, and radiographed in the early 1970s was analyzed, focusing on the aqueduct and components of the midbrain tectum. Methods Photographs of brain dissections and radiographs of the cerebral ventricles and arteries of adult shark, frog, iguana, rabbit, cat, dog, and primate specimens, containing a barium-gelatin radiopaque compound, were analyzed focusing on the aqueduct, the optic ventricles, the quadrigeminal plate, and collicular ventricles. The anatomic information provided by the dissections and radiographs is not reproducible by any other radiopaque contrast currently available. Results Dissected and radiographed cerebral ventricular and arterial systems of the vertebrates demonstrated midbrain tectum changes, including relative size modifications of the mammalian components of the tectum, simultaneously with the enlargement of the occipital lobe. There is a transformation of pre-mammalian optic ventricles to what appear to be collicular ventricles in mammals, as the aqueduct and collicular ventricle form a continuous cavity. Conclusions The mammalian tectum undergoes an evolutionary cephalization process consisting of relative size changes of the midbrain tectum structures. This is associated with enlargement of the occipital lobe, as part of overall neocortical expansion. Potentially, aqueductal anomalies could be explained by evolutionary modifications.

Occipital transtentorial approach for pineal region lesions: Addressing the controversies in conventional teaching

Background: The occipital transtentorial (OT) approach is well-established approach for pineal region tumors and can be of choice for the lesions located around the suboccipital part of tentorium such as the quadrigeminal plate, posterior part of thalamus, tentorial surface of cerebellum, splenial region, posterior falx, and lesions around the tentorial incisura. However, it is not very much extensively used in the above-mentioned locations other than the pineal region. Methods: Thirty-one patients of pineal region lesions were operated by OT approach, the role of conventional preoperative evaluation of the anatomy of the venous sinuses, deep venous system, and tentorial angle was investigated. Results: A variety of lesions were operated using this approach achieving gross and near total resection in majority of the cases (76.6%), with acceptable postoperative mean modified Rankin scales (1.8). Conclusion: The OT is a preferable approach for pineal region lesions for patients of all ages and can be tailored for achieving high resectability rates irrespective of the status of the deep venous system and tentorial angle, with reasonable postoperative surgical outcome.

Diffuse Midline Glioma (H3K27M mutant) in Adult: A Diagnostic Challenge

Introduction: Diffuse midline glioma (DMG), H3K27M mutant is an infiltrative midline high grade glioma with predominantly astrocytic differentiation and K27M mutation in either H3F3A or HIST1H3B/C. Case Report: A 45-year-old female presented with complaints of headache and memory loss for 3 months. MRI was suggestive of an infiltrative mass lesion in the quadrigeminal plate cistern suggestive of pineal neoplasm. Squash and histomorphology showed a low-grade astrocytic tumour with infiltrative growth pattern. Microvascular proliferation and necrosis were absent. Immunohistochemistry showed loss of ATRX protein, focal positivity for p53 proteinand IDH1R132H negativity. On molecular analysis, H3K27M mutation was noted and the case was labelled as DMG H3K27Mmutant (WHO IV) Conclusion: DMG (H3K27M) is a newly added entity in the WHO 4th revised editionof 2016. It presents with a diagnostic challenge as it has varied histomorphology, not requiring atypia, mitosis, endothelial hyperplasia and necrosis for diagnosis as Grade IV.

Surgical management of pineal region lesions

Lesions in the pineal region are topographically located in the centre of the brain in the diencephalic-epithalamic region. An area where the brain is bounded ventrally by the quadrigeminal plate, midbrain tectum, and in-between the left and right superior colliculi, dorsally by the splenium of the corpus callosum, caudally by the cerebellar vermis and rostrally by the posterior aspects of the third ventricle. Major anatomical and surgical challenges are the vein of Galen located dorsally, the precentral cerebellar vein caudally, the internal cerebral veins anteriorly and the basal vein of Rosenthal laterally. Most pineal region tumours can be safely removed by both approaches depending on the surgeon’s experience: the occipital transtentorial approach is recommended in presence of associated hydrocephalus or a steep straight sinus and low location of the tumour and the supracerebellar infratentorial approach for posterior third ventricle tumours.