Surgical anatomy of calvarial skin and bones--with particular reference to neurosurgical approaches

Retrosigmoid Craniectomy with a Layered Soft Tissue Dissection and Hydroxyapatite Reconstruction: Technical Note, Surgical Video, Regional Anatomy, and Outcomes

Introduction There are many reported modifications to the retrosigmoid approach including variations in skin incisions, soft tissue dissection, bone removal/replacement, and closure.

Objective The aim of this study was to report the technical nuances developed by two senior skull base surgeons for retrosigmoid craniectomy with reconstruction and provide anatomic dissections, surgical video, and outcomes.

Methods The regional soft tissue and bony anatomy as well as the steps for our retrosigmoid craniectomy were recorded with photographs, anatomic dissections, and video. Records from 2017 to 2019 were reviewed to determine the incidence of complications after the authors began using the described approach.

Results Dissections of the relevant soft tissue, vascular, and bony structures were performed. Key surgical steps are (1) a retroauricular C-shaped skin incision, (2) developing a skin and subgaleal tissue flap of equal thickness above the fascia over the temporalis and sub-occipital muscles, (3) creation of subperiosteal soft tissue planes over the top of the mastoid and along the superior nuchal line to expose the suboccipital region, (4) closure of the craniectomy defect with in-lay titanium mesh and overlay hydroxyapatite cranioplasty, and (5) reapproximation of the soft tissue edges during closure. Complications in 40 cases were pseudomeningocele requiring shunt (n = 3, 7.5%), wound infection (n = 1, 2.5%), and aseptic meningitis (n = 1, 2.5%). There were no incisional cerebrospinal fluid leaks.

Conclusion The relevant regional anatomy and a revised technique for retrosigmoid craniectomy with reconstruction have been presented with acceptable results. Readers can consider this technique when using the retrosigmoid approach for pathology in the cerebellopontine angle.

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.

The diploic venous system: surgical anatomy and neurosurgical implications

Object

There are few systematic investigations of the dissected surgical anatomy of the diploic venous system (DVS) in the neuroanatomical literature. The authors describe the DVS relative to different common neurosurgical approaches. Knowledge of this system can help avoid potential sources of unacceptable bleeding and may impact healing of the cranium.

Methods

Using a high-speed drill with a 2-mm bit, the authors removed the outer layer of the compact bone in the skull to expose the DVS in 12 formalin-fixed cadaver heads. Pterional, supraorbital, and modified orbitozygomatic craniotomies were performed to delineate the relationship of the DVS.

Results

The draining point of the frontal diploic vein (FDV) was located near the supraorbital notch. The draining point of the anterior temporal diploic vein (ATDV) was located in all pterional areas; the draining point of the posterior temporal diploic vein (PTDV) was located in all asterional areas. The PTDV was the dominant diploic vessel in all sides. The FDV and ATDV could be damaged during supraorbital, modified orbitozygomatic, and pterional craniotomies. The anterior DVS connected with the sphenoparietal and superior sagittal sinus (SSS). The posterior DVS connected with the transverse and sigmoid sinuses and was the dominant diploic vessel in all 24 sides. Of all the major diploic vessels, the location and pattern of distribution of the FDV were the most constant. The parietal bone contained the most diploic vessels. No diploic veins were found in the area delimited by the temporal squama.

Conclusions

The pterional, orbitozygomatic, and supraorbital approaches place the FDV and ATDV at risk. The major anterior diploic system connects the SSS with the sphenoparietal sinus. The posterior diploic system connects the SSS with the transverse and sigmoid sinuses.