Accessing the Porcine Brain via High-Speed Pneumatic Drill Craniectomy

Summary

This protocol describes performing a craniectomy using a high-speed pneumatic drill on a 3-month-old Danish Landrace pig. The access is made through the frontal bone and reveals the ventral dura mater and underlying cerebral hemispheres. This procedure allows for access to a large portion of the pig brain.

Abstract

The use of pigs as an experimental animal model is especially relevant in neuroscience research, as the porcine and human central nervous systems (CNS) share many important functional and architectural properties. Consequently, pigs are expected to have an increasingly important role in future research on various neurological diseases. Here, a method to perform an anterior craniectomy through the porcine frontal bone is described. After a midline incision and subsequent exposure of the porcine frontal bone, anatomical landmarks are used to ensure the optimal location of the craniectomy. By careful and gradual thinning of the frontal bone with a rounded drill, a rectangular opening to the dura mater and underlying cerebral hemispheres is achieved. The presented method requires certain surgical materials, including a pneumatic high-speed drill, and some degree of surgical experience. Potential complications include unintended lesions of the dura mater or dorsal sagittal sinus. However, the method is simple, time-efficient, and offers a high degree of reproducibility for researchers. If performed correctly, the technique exposes a large portion of the unaffected pig brain for various neuromonitoring or analyses.

Introduction

In general, animal models are used when practical and/or ethical limitations prohibit the use of human patients to examine diseases or test surgical methods. Novel animal models are generally established to provide new knowledge with translational value to human conditions. Rodents are often utilized due to practical and financial considerations, but they have limited translational value to humans, especially due to substantial anatomical differences¹. Pigs, however, offer several advantages compared to rodents. Not only do pigs share several key anatomical, physiological, metabolic, and genetic features with humans, but the size of the porcine organ systems can be weight-matched to resemble human organs^2,3. This gives pigs a unique role among surgical animal models and in procedural training⁴. Although the use of porcine models requires certain practical and financial capabilities compared to the use of rodents, pigs offer both a financially and ethically more acceptable option compared to the use of non-human primates.

The porcine brain is of particular interest in translational neuroscience research. Firstly, the architecture of the pig brain is similar to that of the human brain, as both are white matter-predominant and gyrencephalic^3,5,6. Secondly, the larger brain size in pigs compared to rodents permits the use of surgical equipment and various imaging modalities equivalent to those used in clinical settings^7,8. Consequently, various porcine models have been used extensively in neuroscience research over recent decades⁹. The majority of these porcine CNS models, however, require direct analysis of brain tissue, which can be obtained in various ways (e.g., implantation of catheters or electrodes, tissue biopsies, etc.)¹⁰. Since most of these modalities require some degree of instrumentalization and direct access to the brain, different approaches for surgical access must be considered.

This method involves performing an anterior craniectomy through the frontal bone on a sedated 3-month-old female Danish Landrace pig. The overall purpose of this manuscript is to describe a method for exposing a large proportion of the ventral porcine brain through a craniectomy using a pneumatic high-speed drill. The first step is to place the subject in a suitable position with an elevated head. Since the porcine cranium is quite different from that of humans, the second step involves planning the placement of the craniectomy using various anatomical landmarks. The third step is to access the underlying dura mater covering both hemispheres without damaging it.

Protocol

All animal experiments described were performed at Aalborg University Hospital, Denmark, in accordance with existing laws and under the approval of the Danish Animal Experiments Inspectorate (license no. 2020-15-0201-00401). Domestic swine, female, approximately 40 kg and 3 months of age, were used for this study. The details regarding the reagents and equipment used are listed in the Table of Materials. 1. Subject housing House subjects in groups …

Representative Results

The prone position of the pig's head provides optimal access for the surgeon during the procedure, and the use of stabilizing sandbags reduces the risk of unintended shifts in the pig's head position while drilling. During this demonstration, the superficial anatomical landmarks of the pig's superior skull (both superior orbital crests and the nuchal crest) (Figure 1 and Figure 3) were used to precisely identify the center…

Discussion

The demonstrated procedure involves several critical steps. Firstly, the accurate planning of the craniectomy's location is crucial due to the composition of the porcine skull. Since the thickness of the porcine frontal bone increases at the lateral edges, placing the opening too laterally¹¹ can make it difficult to reach the dura mater during drilling. Additionally, locating the opening correctly within the midline is important to reduce the risk of unintended damage to the underlying dorsal …

Materials

10 mL plastic syrringes	Becton, Dickinson and Company	303219
107 Microdialysis pump	M Dialysis	P000127	107 Microdialysis Pump
2 mL plastic syrringes	Becton, Dickinson and Company	300928
25 mm, 18 G needles	Becton, Dickinson and Company	304100
Bair Hugger heater	3M	B5005241003
Bair Hugger heating blanket	3M	B5005241003
Batery for microdialysis pump	M Dialysis	8001788	Battery 6V, 106 & MD Pump
Dissector	Karl Storz	223535	Flattended 3 mm dissector
Endotracheal tube size 6.5	DVMed	DVM-107860	Cuffed endotracheal tube
Euthasol Vet	Dechra Veterinary Products A/S	380019	phentobarbital for euthanazia, 400 mg/mL
Farabeuf Rougine	Mahr Surgical		Flat headed rougine (12 mm)
Foley Catheter 12 F	Becton, Dickinson and Company	D175812E	Catherter with in-built thermosensor
Intravenous sheath	Coris Avanti		Avanti Cordis Femoral Sheath 6 F
Microdialysis brain catheters	M Dialysis	P000050	membrane length 10 mm -shaft 100 mm 4/pkg
Microdialysis syringe	M Dialysis	8010191	106 Pump Syringe 20/pkg
Microvials for microdialysis sampling	M Dialysis	P000001	Microvials 250/pkg
Operating table
Pneumatic high-speed drill	Medtronic		Medtronic Midas Rex 7 drill
Primus respirator	Dräger		Respirator with in-built vaporiser for supplementary Sevofluran anesthesia
Rounded diamond drill	Medtronic	7BA40D-MN
Self-retaining retractor	World Precission Instruments	501722	Weitlander retractor, self-retaining, 14 cm blunt
Sterile Saline	Fresnius Kabi	805541	1000 mL
Sterile surgical swaps
Surgical scalpel no 24	Swann Morton	5.03396E+12	Swann Morton Sterile Disposable Scalpel No. 24
Zoletil Vet	Virbac		Medical mixture for induction of anesthesia