Standardization of the technique of silicon injection of human cadaveric heads for opacification of cerebral vasculature in Indian conditions
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.227303
Source of Support: None, Conflict of Interest: None
Keywords: Anatomical dissection of brain, anatomy, cerebral blood vessels, silicon injection
Anatomical studies on cadaveric heads have become one of the most useful methods for educating neurosurgeons regarding the surgical anatomy of the brain and skull base. The relevance of such studies is universal, and cadaveric dissection is still considered to be the gold standard for ex-vivo simulation among all the models employed for neurosurgical training. Dye injection of the cranial vascular tree that permits the opacification of the arterial and venous system in different colors has dramatically transformed the visual impression formed upon the trainee by anatomical dissections.
The technique of silicon injection in the cranial vasculature of cadaveric heads has been well described in the literature,,, but the results have been significantly influenced by the method of cadaver preparation, the operator's experience, and the ambient conditions in which the specimens are preserved. Despite continuing efforts, till now, the technique and materials for the injection of blood vessels of the cadaveric human heads in Indian conditions have not been standardized. Due to the socio-religious constraints and poor acceptance of postmortem donation of bodies, human cadavers are precious and quite difficult to procure in India. They, therefore, cannot possibly be utilized for repeated experimentation, which is an inevitable step in the standardization of any dye injection technique.
Accordingly, in this study, we have attempted to establish a reliable and inexpensive biological model for testing the dye injection techniques and their concentrations. We also describe the application of these techniques to human cadaveric heads.
The testing protocol was reviewed and approved by the institutional ethics committee. The study was conducted in two phases described below.
The first phase was concerned with the standardization of the dye injection and the cadaveric preservation technique. For this phase, eight fresh goat heads sectioned at the neck were procured from butchers as they are inexpensive, widely available, and their use for experimentation is ethically permissible. Bilateral internal carotid arteries and internal jugular veins were dissected and copiously irrigated with tap water till the return was clear and free of blood clots. Once there was free flow of water from the corresponding vessels on the opposite side, bilateral internal carotid arteries and internal jugular veins were cannulated with different sizes of commonly available tubings based on the size of the vessels. The tubes were firmly secured inside the vessels with the help of sutures. This step was important as considerable pressure has been required to inject the viscous dye into the blood vessels, and during this process, the tubes tend to back out of the vessel lumen. Distension of the vascular tree with tap water injected through the carotid arteries helps to distend the great veins, which are otherwise floppy and difficult to isolate from the surrounding soft tissue. The vascular tree was then irrigated with the preservation and fixation solution and clamped for 30 minutes. Blue and red-colored silicone rubber dyes (Biodur ® GmBh, Germany) were then prepared as per the specifications described in [Table 1].
Red dye was injected into the carotid vessels to opacify the arterial vasculature, and blue dye was injected into the internal jugular vein to delineate the venous vasculature [Figure 1]. A 50-cc syringe was used to inject the colored silicone till the dye egressed from the contralateral corresponding vessel. The ipsilateral vessel was then clamped, and the dye was injected from the contralateral vessel under considerable pressure to ensure that the dye penetrated up to the smaller ramifications of the vascular tree. The injected specimens were immersed in a solution of formalin, absolute alcohol, and distilled water for a fortnight. Initially, we started with 15% formalin solution. We, then, titrated the solution concentration to ensure a proper concentration of the constituent chemicals, based upon our observations following dissection of the specimens. A small craniotomy was then performed around the vertex of the cranium. The condition of the brain and quality of the injection in the dural as well as cortical vessels were observed.
In the second phase, we injected dyes into four human cadaveric heads following the same technique standardized in the goat's head. All the injections were performed in bodies donated to the Anatomy Department of the institute. The regulations pertaining to these donations did not permit decapitation of the bodies immediately after donations.
Dissection, cannulation, and preparation of the vascular tree in the human head
The carotid arteries and the internal jugular veins were dissected in a fairly straightforward manner after isolating the carotid sheath through a standard vertical incision along the medial border of the sternocleidomastoid (SCM) muscle. These vessels were then cannulated with appropriate sized tubes. The tubes were secured inside the vessel lumen with silk threads for up to a length of 4 cm along the course of the vessels.
The exposure of the vertebral arteries in the neck was more challenging. The lower part of the vertical incision in the neck was extended to the suprasternal notch. The sternal head of the SCM was divided close to its origin to enlarge the exposure. The dissection was carried out between the reflected part of SCM laterally and the internal jugular vein medially. The vertebral artery was identified as it entered the transverse foramen of the C6 vertebra (just medial to the Chassaignac's tubercle) in the triangle between the anterior scalene muscle and the longus colli muscle [Figure 2]. It was carefully cannulated with appropriate sized tubings.
The carotid arteries and veins were then liberally irrigated with normal saline till the returning fluid was free of clots. The irrigation fluid had a tendency to ooze out from small tributaries of the jugular veins, which might have been inadvertently divided during dissection of the internal jugular vein. These tributaries were then carefully ligated to seal off the venous system before the dye injection.
The egress of the irrigating fluid from the vertebral arteries upon flushing the carotids was reassuring as it ensured the complete coverage of the circle of Willis and the possibility of a satisfactory arterial injection. Once the vascular tree was free from clots, it was irrigated with 10% formalin solution. The tubes within the vessels were then identified, labelled, and clamped and the heads were left for 3–4 days for the formalin solution to act.
The dyes were then prepared and injected in a manner described above for the goat's head. A small amount of dye was retained in the chamber of the injecting syringe to observe its polymerization.
Following the dye injection, the bodies were immersed in a formalin tank for at least 21 days. After due permission was sought from the interested parties for decapitation of the body, the neck was sectioned near its root, and the head was used for dissection.
To determine the appropriate concentration of formalin required for best results to be achieved following dye injection, we experimented with several compositions of the preserving fluid into which the goat heads were immersed following dye injection. Our observations are summarized in [Table 2]. [Figure 3] shows our observations upon dissection of a well-preserved specimen of the injected goat's head.
Upon dissecting the four cadaveric human heads which were injected with silicon dyes and preserved in 10% formalin, the vessels were all well-opacified and the brain was of near normal consistency and good for dissection [Figure 4].
Pros and cons of the technique
A surgeon's understanding of the surgical anatomy can be greatly enhanced by the dissection of preserved cadaveric specimens. Among neurosurgeons, the realization of the importance of cadaveric dissection is evidenced by the fact that cadaver courses are increasingly being organized around the globe and are seeing an enthusiastic attendance. They have almost become a necessary prelude to all national and international conferences. However, cadaveric dissection is often an unpleasant task even for the most determined anatomist, chiefly because of the pungency of the embalming solutions used in cadaver preparation. In an earlier publication, we have described the usual process of cadaver procurement and processing for laboratory dissection. Formaldehyde has been adapted as the standard embalming solution for cadavers since the late 19th century. Its advantages include its low cost, excellent preservation properties especially for the brain tissue, antimicrobial activity, and easy availability.
On the other hand, formaldehyde solutions are associated with a disagreeable odor, produce troublesome tissue rigidity, and there are potential risks for the operator who may develop a malignancy from the long term exposure to formaldehyde. To avoid the undesirable effects of formalin preservation, several alternative liquids have been experimented with. Ethyl alcohol offered excellent tissue preservation, but the fixation of the brain was unsatisfactory. The most agreeable alternative, therefore, was low formalin embalming which could reduce the carcinogenic potential of formalin but retain its antimicrobial activity. Some workers have experimented with formalin concentrations as low as 2.3%, but in our case, very low formalin concentrations rendered the preservation of brain unpredictable.
We obtained a favorable consistency of the brain without features of putrefaction on preserving sheep head with 10% formalin. The above concentration of formaldehyde and alcohol was also applicable for preserving human cadaver head for silicon dye injection. Specimens preserved in 10% formalin were also devoid of any disagreeable odor and prolonged dissection sessions were possible without any inconvenience. Between the dissection sessions, the formalin-treated specimens were preserved in freezers maintaining an ambient temperature of −20°C. The tissues of these cadaveric specimens were quite rigid immediately upon bringing them out of the freezer because of the formation of ice crystals inside them. Immersion of the specimens in warm water for a few hours considerably softened them and facilitated the subsequent dissection considerably.
Obtaining a satisfactory vascular injection in a human cadaver head during the initial attempts may be usually troublesome and sometimes annoying. The method of preparation and dye injection for decapitated human heads is well described in the literature.,, The best injections are obtained when the heads are processed as early after death as possible. However, under Indian conditions, early decapitation of the donated bodies is often not permissible. Hence, the technique should be modified for heads not sectioned at the neck, which we have described in this paper.
To capture the nuances of the technique, it should be practiced and perfected over a biological model, which is inexpensive, easily available, and ethically permissible. A goat's head sourced from the butcher fulfills all the requirements for such a model. We have also shown that observations from this model could be directly translated to dye injection methods in human heads. Though the dyes that we used for this study were custom made by a foreign manufacturer and were expensive, the goat model offers an opportunity to test indigenously manufactured polymerizing dyes in the future, which has the potential to considerably reduce the cost of cadaver preparation.
The anatomy of the goat's brain is considerably different from the human brain and will not probably contribute to further understanding of the human anatomy. However, the color, texture, and the handling of the goat's brain is similar and can offer useful lessons in microsurgical dissection skills for residents and trainees.,
Goat heads can provide a convenient and suitable model for developing and refining vascular injection techniques required for preparing cadaveric human heads for microsurgical dissection.
The facilities for cadaver dissection, photography and archiving was provided by the Department of Biotechnology, Department of Science and Technology and Department of Health Research funded state-of-the-art Neurosurgery Education and Skills Training School at AIIMS, New Delhi. The human cadaveric specimens were procured through the Department of Anatomy, AIIMS, New Delhi.
Financial support and sponsorship
Intramural research grant from AIIMS for the financial year 2015–2016.
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]