The Dorsal Sagittal Venous Sinus Anatomical Variations in Brachycephalic, Dolichocephalic, and Mesocephalic Dogs and Their Significance for Brain Surgery

Standard and modified glabellar flap for medial canthus reconstruction following mass removal in three dogs and two cats

PURPOSE

To describe the surgical technique and clinical outcomes of the glabellar flap and its modification for the reconstruction of the medial canthus following resection of tumors in three dogs and two cats.

METHODS

Three dogs (7-, 7-, and 12.5-year-old mixed breeds) and two cats (10- and 14-year-old Domestic shorthair) presented with a 7-13 mm tumor affecting the eyelid and/or conjunctiva in the medial canthal region. Following en bloc mass excision, an inverted V-shaped skin incision was made in the glabellar region (i.e., the area between the eyebrows in humans). The apex of the inverted V-shaped flap was rotated in three cases, whereas a horizontal sliding movement was performed in the other two cases to better cover the surgical wound. The surgical flap was then trimmed to fit the surgical wound and sutured in place in two layers (subcutaneous and cutaneous).

RESULTS

Tumors were diagnosed as mast cell tumors (n = 3), amelanotic conjunctival melanoma (n = 1), and apocrine ductal adenoma (n = 1). No recurrence was noted in a follow-up time of 146 ± 84 days. Satisfactory cosmetic outcome with normal eyelids closure was achieved in all cases. Mild trichiasis was present in all patients and mild epiphora was noted in 2/5 patients, but there were no associated clinical signs such as discomfort or keratitis.

CONCLUSIONS

The glabellar flap was easy to perform and provided a good outcome in terms of cosmetic, eyelid function, and corneal health. Postoperative complications from trichiasis appear to be minimized by the presence of the third eyelid in this region.

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.

Folding drives cortical thickness variations

The cortical thickness is a characteristic biomarker for a wide variety of neurological disorders. While the structural organization of the cerebral cortex is tightly regulated and evolutionarily preserved, its thickness varies widely between 1.5 and 4.5 mm across the healthy adult human brain. It remains unclear whether these thickness variations are a cause or consequence of cortical development. Recent studies suggest that cortical thickness variations are primarily a result of genetic effects. Previous studies showed that a simple homogeneous bilayered system with a growing layer on an elastic substrate undergoes a unique symmetry breaking into a spatially heterogeneous system with discrete gyri and sulci. Here, we expand on that work to explore the evolution of cortical thickness variations over time to support our finding that cortical pattern formation and thickness variations can be explained - at least in part - by the physical forces that emerge during cortical folding. Strikingly, as growth progresses, the developing gyri universally thicken and the sulci thin, even in the complete absence of regional information. Using magnetic resonance images, we demonstrate that these naturally emerging thickness variations agree with the cortical folding pattern in n = 9 healthy adult human brains, in n = 564 healthy human brains ages 7-64, and in n = 73 infant brains scanned at birth, and at ages one and two. Additionally, we show that cortical organoids develop similar patterns throughout their growth. Our results suggest that genetic, geometric, and physical events during brain development are closely interrelated. Understanding regional and temporal variations in cortical thickness can provide insight into the evolution and causative factors of neurological disorders, inform the diagnosis of neurological conditions, and assess the efficacy of treatment options.

Morphogenesis of Canine Chiari Malformation and Secondary Syringomyelia: Disorders of Cerebrospinal Fluid Circulation

Chiari-like Malformation (CM) and secondary syringomyelia (SM), as well as their analogous human conditions, is a complex developmental condition associated with pain and accompanying welfare concerns. CM/SM is diagnosed ever more frequently, thanks in part to the increased availability of magnetic resonance imaging in veterinary medicine. Research over the last two decades has focused primarily on its pathophysiology relating to overcrowding of the cranial caudal fossa. More recent characterizations of CM/SM include brachycephaly with osseous reduction and neural parenchymal displacement involving the entire brain and craniocervical junction to include rostral flattening, olfactory bulb rotation, increased height of the cranium, reduced cranial base with spheno-occipital synchondrosis angulation, reduced supraoccipital and interparietal crest and rostral displacement of the axis and atlas with increased odontoid angulation. The most shared manifestation of CM is the development of fluid-filled pockets (syrinx, syringes) in the spinal cord that can be readily quantified. Dogs with symptomatic CM without SM have a reduced basioccipital bone, compensatory increased cranial fossa height with displaced parenchyma whereby the cerebellum is invaginated beneath the occipital lobes but without compromising cerebrospinal fluid channels enough to cause SM. Thus, broadly defined, CM might be described as any distortion of the skull and craniocervical junction which compromises the neural parenchyma and cerebrospinal fluid circulation causing pain and/or SM. The etiology of CM is multifactorial, potentially including genetically-influenced, breed-specific abnormalities in both skeletal and neural components. Since causation between specific morphologic changes and SM or clinical signs is unproven, CM might be more appropriately considered as a brachycephalic obstructive CSF channel syndrome (BOCCS) rather than a single malformation. Understanding the normal development of the brain, skull and craniocervical junction is fundamental to identifying deviations which predispose to CM/SM. Here we review its anatomical, embryological, bio-mechanical, and genetic underpinnings to update the profession's understanding of this condition and meaningfully inform future research to diminish its welfare impact.

Using Bronson Equation to Accurately Predict the Dog Brain Weight Based on Body Weight Parameter

The study used 69 brains (n = 69) from adult dog cadavers, divided by their skull type into three groups, brachi (B), dolicho (D) and mesaticephalic (M) (n = 23 each), and aimed: (1) to determine whether the Bronson equation may be applied, without reservation, to estimate brain weight (BW) in brachy (B), dolicho (D), and mesaticephalic (M) dog breeds; and (2) to evaluate which breeds are more closely related to each other in an evolutionary scenario. All subjects were identified by sex, age, breed, and body weight (bw). An oscillating saw was used for a circumferential craniotomy to open the skulls; the brains were removed and weighed using a digital scale. For statistical analysis, p-values < 0.05 were considered significant. The work demonstrated a strong relationship between the observed and predicted BW by using the Bronson equation. It was possible to hypothesize that groups B and D present a greater encephalization level than M breeds, that B and D dog breeds are more closely related to each other than to M, and from the three groups, the D individuals presented the highest brain mass mean.

Insight of Dogs' Inner Mandible Anatomy using Mathematical Models

This study was performed in a sample of 20 dogs (n = 20) and aimed to: (1) characterize the mandible height (Mh), mandibular canal height (MCh) and distance between the inter-dental alveolar margin and the mandibular canal (dIAM-MC) dimensions, and (2) to develop mathematical models that express the insight's mandible anatomy of those important mandible structural elements allowing the prediction of their dimensions using physical parameters such as patient body weight (Wg) and the canine tooth width at the free gingival margin level-(wCGM). Lateral-view X-rays of both sides of the skull were taken for all the individuals. Three mathematical prediction models were developed to calculate Mh, MCh and dIAM-MC. Achieved proportions of the mandible considered parameters regarding its height were of 36.45% for MCh, 50.90% for dMAI-MC and 12.65% for vMC. Statistically significant differences were registered between the Wg and wCGM (P = 0.00), Mh (P = 0.00), MCh (P = 0.00) and dIAM-MC (P = 0.00). Only the Wg presented a strong correlation with the wCGM (R = 0.58), Mh (R = 0.70), dIAM-MC (R = 0.60) and MCh (R = 0.68). These models will allow a clinician to estimate the size of the mandible structures by only using data obtained during the physiological examination, with a sufficiently high prediction capacity and a very low standard error. The study points out the relationships of physiological parameters such as Wg and wCGM with mandible anatomical structural elements considered as important in oral surgery. The results of this study give the surgeon a new additional tool providing more information on the mandible anatomical structures and its relationships. This reduces the risk of iatrogenic lesions during the oral surgical procedures and improves patient safety.

Morphological Variations in the Transverse Venous Sinus Anatomy of Dogs and its Relationship to Skull Landmarks

We characterized the anatomical morphology of the transverse venous sinus (TVS) of 69 canine adult cadavers belonging to three groups: brachycephalic (B), dolichocephalic (D) and mesaticephalic (M). In addition, we outlined its path over the skull using five classic human craniometric points (CPs): the asterion (ast), the bregma (b), the glabella (g), the stephanion (st) and the pterion (pt). The study aimed to establish anatomical differences in the TVS between groups and in the relationship between the TVS and skull. We found that TVS anatomy and its relationships to skull landmarks vary markedly between the groups, with similar anatomical arrangements in B and M. The TVS length can be ranked as M < B < D (with D being the biggest), whereas the width can be ranked as M < D < B (with B being the widest) with the right side being smaller than the left. In the B and M groups, the TVS assumes a craniocaudal trajectory that is closer to the lateral skull wall than in D, where the TVS presents a caudocranial direction. By documenting the morphological characteristics of the TVS, we can create a set of anatomical references allowing construction of a basic framework to greatly decrease the probability of TVS injury during neuronavigation procedures when supported by a good knowledge of the skull, brain anatomies and their relationships.

Longitudinal Cerebral Fissure Anatomy Variations in Brachy-, Dolicho- and Mesaticephalic Dogs and Their Importance to Brain Surgery

The study used a sample of 69 formalin-fixed brains from adult dog cadavers (n = 69) and aimed (1) to characterize the longitudinal cerebral fissure (LCF) anatomy in brachy-(B), dolicho-(D) and mesaticephalic-(M) dogs and their potential differences, and (2) to establish cranioencephalic relationships between the LCF and five classical craniometric points(cp): asterion(ast), bregma(b), stephanion(st), glabella(g), and pterion(pt). Anatomical records were collected using a digital caliper, and for statistical analysis P-values < 0.05 were considered significant. The LCF length can be ranked, in ascending order as B < D < M, and if used as a surgical corridor, the M group had the greatest surgical corridor area, and the D group the smallest. LCF morphology was uniform among the three groups exhibiting dilated anterior(AR) and posterior(PR) regions and narrow middle region, where the most marked differences were registered. The LCF AR is the ideal spot to begin brain surgery if the LCF is to be used as a surgical corridor in B and M, while the LCF PR should be considered in D. The five cp selected were quite useful to understand LCF anatomical morphology, its projections over the external skull surface, and to establish cranioencephalic relationships between the LCF and vault; allowing us to consider the vault anterior area in B, and in M, and the vault posterior area in D for craniotomy initial burr-hole placement. As for the distance from the cp projections in the brain surface to the LCF regions, major differences were registered by comparing the B group with the other two, and for both hemispheres.