Patterns of the Cranial Venous System from the Comparative Anatomy in Vertebrates. Part II.The Lateral-Ventral Venous System

Canine Intracranial Venous System: A Review

The intracranial venous system (ICVS) represents in mammals a complex three-dimensional structure, which provides not only for adequate brain perfusion, but has also a significant impact on: cerebrospinal fluid (CSF) resorption, maintaining of the intracranial pressure (ICP), and brain thermoregulation. An intimate understanding of the anatomy and physiology of ICVS is fundamental for neurological diagnostics, selection of therapeutic options, and success of neurosurgical procedures in human and veterinary medicine. Since the intracranial interventions in dogs are recently performed more frequently than twenty or thirty years ago, the authors decided to review and report on the basic knowledge regarding the complex topic of morphology and function of the canine ICVS. The research strategy involved an NCBI/NLM, PubMed/MED-LINE, and Clarivate Analytics Web of Science search from January 1, 1960, to December 31, 2021, using the terms “canine dural venous sinuses” and “intracranial venous system in dogs” in the English language literature; also references from selected papers were scanned and relevant articles included.

Comparative morphology of snake (Squamata) endocasts: evidence of phylogenetic and ecological signals

Brain endocasts obtained from computed tomography (CT) are now widely used in the field of comparative neuroanatomy. They provide an overview of the morphology of the brain and associated tissues located in the cranial cavity. Through anatomical comparisons between species, insights on the senses, the behavior, and the lifestyle can be gained. Although there are many studies dealing with mammal and bird endocasts, those performed on the brain endocasts of squamates are comparatively rare, thus limiting our understanding of their morphological variability and interpretations. Here, we provide the first comparative study of snake brain endocasts in order to bring new information about the morphology of these structures. Additionally, we test if the snake brain endocast encompasses a phylogenetic and/or an ecological signal. For this purpose, the digital endocasts of 45 snake specimens, including a wide diversity in terms of phylogeny and ecology, were digitized using CT, and compared both qualitatively and quantitatively. Snake endocasts exhibit a great variability. The different methods performed from descriptive characters, linear measurements and the outline curves provided complementary information. All these methods have shown that the shape of the snake brain endocast contains, as in mammals and birds, a phylogenetic signal but also an ecological one. Although phylogenetically related taxa share several similarities between each other, the brain endocast morphology reflects some notable ecological trends: e.g. (i) fossorial species possess both reduced optic tectum and pituitary gland; (ii) both fossorial and marine species have cerebral hemispheres poorly developed laterally; (iii) cerebral hemispheres and optic tectum are more developed in arboreal and terrestrial species.

Embryological Consideration of Dural Arteriovenous Fistulas

The topographical distribution of dural arteriovenous fistulas (DAVFs) was analyzed based on the embryological anatomy of the dural membrane. Sixty-six consecutive cases of intracranial and spinal DAVFs were analyzed based on the angiography, and each shunt point was identified according to the embryological bony structures. The area of dural membranes was categorized into three different groups: a ventral group located on the endochondral bone (VE group), a dorsal group located on the membranous bone (DM group) and a falco-tentorial group (FT group) located in the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragm sellae. The FT group was designated when the dural membrane was formed only with the dura propria (meningeal layer of the dura mater) and not from the endosteal dura. Cavernous sinus, sigmoid sinus, and anterior condylar confluence was categorized to VE group, which had a female predominance, more benign clinical presentations, and a lower rate of cortical and spinal venous reflux. Transverse sinus, confluence, and superior sagittal sinus belonged to the DM group. Olfactory groove, falx, tent of the cerebellum, and nerve sleeve of spinal cord were categorized to the FT group, which presented later in life and which had a male predominance, more aggressive clinical presentations, and significant cortical and spinal venous reflux. The DAVFs was associated with the layers of the dural membrane characterized by the two different embryological bony structures. The FT group was formed only with the dura propria as an independent risk factor for aggressive clinical course and hemorrhage of DAVFs.

Non-standard intracranial connections and alternative pathways between dural venous sinuses and cerebral veins in the rat

The aim of this study was to describe the uncommon intracranial venous connections and vein structures that may play a role in the redirection of cerebral blood drainage. The study was carried out on 35 adult Wistar rats. Corrosion casts were prepared from the cerebral venous system and Spofacryl® was used as a casting medium. The highest prevalence of non-standard connections and variations was noted in the region of sinus petrosus dorsalis (SPD) (31.2 %) and v. cerebri magna (VCM) (28.5 %). SPD established a non-standard anastomosis with sinus petrosus ventralis in 8.6 % of cases, with sinus interperiopticus in 2.8 % of cases, with sinus sigmoideus in 5.7 % of cases and with confluens sinuum (CS) in 2.8 % of cases, where higher prevalence was observed on the left side of the brain. In 11.4 % of cases VCM formed a secondary connection between CS and sinus rectus leading to the formation of the loop. In a similar manner, VCM entered the sinus transversus in 8.6 % of cases, while in 5.7 % of cases VCM merged with SPD and formed an unusual connection among dorsal and ventral systems of sinuses. Several sinuses were observed as inconsistent, including sinus occipitalis (14.3 %), sinus intercavernosus rostralis (22.8 %) and sinus interbasilaris (14.3 %). The hypoplastic posterior and anterior anastomotic vein did not reach one another in 20 % of observed cases. Anatomical information concerning different drainage pathways are important in preoperative planning and can provide necessary understanding in experimental studies, including cerebral vein occlusion, venous infarction, or experimentally induced cerebral venous obstruction.