Microsurgical Training Model with Nonliving Swine Head. Alternative for Neurosurgical Education 1

PURPOSE: This paper proposes a practical model of microneurosurgical training using a nonliving swine head. METHODS: Fresh porcine heads were obtained from butchery and dissected at our Laboratory of Microsurgery. Brain and skull base surgery were trained under microscopic magnification. RESULTS: Several neurosurgical procedures could be simulated in the nonliving pig model, including transcallosal approach to the lateral ventricle, lateral sulcus and middle fossa dissection, and posterior fossa surgery. CONCLUSION: The swine model perfectly simulates standard microneurosurgical procedures, and is a useful tool for developing and refining surgical skills.


Introduction
Laboratory training models are essential for developing and refining surgical skills.In addition to the improvement of technical proficiency, it provides a way to reduce risks to the patients.Ideally, the mastery of surgical techniques should be obtained first in the laboratory before being used in clinical practice 1,2 .
Historically, several animal models were employed in order to provide surgical training.However, increasing sensitivity toward ethical aspects, strict legislation, and a greater public awareness, strongly require a significant decrease in using live animal models 3 .
Several training models were described in literature in order to reduce the use of live animals for surgical education [3][4][5][6] .
As a result, nonliving animal tissues has become increasingly attractive on a cost basis, and these models are "closer-to-real-life" scenario compared to the prosthetic models, such as gloves and silicone tubes.
Swine has been used as a model of surgical training such as neurolysis and microvascular suture techniques with pig foreleg, and coronary arteries anastomosis with porcine heart 3 .In neuroscience the pig model was also used due to its similarities with the human brain 7 .Some authors have described an in vivo swine model for training neurosurgical residents 8 .
In view of the need of refining surgical skills and of reduce the use of live animals this paper suggests a practical model of neurosurgical training using a nonliving pig head.

Methods
Fresh swine heads were obtained from local butchery at a relatively low cost (US$ 5.00/each) (Figure 1A).The head was kept in a refrigerator at 4°C for six hours after it was slaughtered.
Then, at our Laboratory of Microsurgery at Neurological Institute of Curitiba, was performed skin incision (Figure 1B), temporal muscle dissection (Figure 1C), and large craniotomy, with care taken to preserve the underlying dura (Figure 1D).
Brain and skull base surgery under microscope magnification were first simulated using fresh specimens.
Subsequently, the porcine heads were embedded in formaldehyde 10% solution in order to increase the durability of the specimens.
Neurosurgical training steps were performed in an operating microscope (OpMi Zeiss Inc., Germany) with the use of microsurgical instruments, suction tube and drill (Figure 2).After craniotomy, an extensive dural open was performed exposing the supratentorial and infratentorial structures (Figure 3).

Results
Several microneurosurgical procedures could be performed in the nonliving pig model.At first, interhemispheric fissure was dissected to visualize cingulated gyri, callosomarginal and pericallosal arteries.In the sequence, a transcallosal approach to the lateral ventricle and to the area of the foramen of Monroe could be accomplished (Figure 4).
Forth ventricle and cranial nerves were dissected and visualized at the brainstem (Figure 6A and 6B).The cerebellum was partially resected to expose the cerebellopontine angle (Figure 6C).Drilling of internal auditory canal could also be accomplished.A review in the literature depicts several models described for surgical education, including human cadaveric specimens 6 , resected human tissues 9 , live animals 10 , synthetic materials, and nonliving animals.The main disadvantages of using human cadavers are the cost and the difficulty associated to the obtainment.Also, significant reduction in live animals training was expected due to strict legislation, a major public awareness, and an increasing sensitivity toward ethical aspects 3 .
Nonliving animals models are readily available at low cost and have been proposed as an alternative to prevent animal deaths.Nonliving animals may also mimic human anatomy and are more realistic comparing to synthetic materials, especially with fresh specimens usage.The major disadvantage of the model is the lack of a dynamic circulation 11 .
Achar et al. 5 proposed an interesting model of vascular anastomosis training using esophagus and trachea of nonliving chicken.Hino described a training exercise for microarterial anastomosis using a chicken wing artery 12 .These methods proved to be useful for learning microsurgical techniques and several advantages can be noted, including low cost and easiness to handle.
Neurosurgical training with nonliving animals were also reported.Hicdonmez et al. 13 described a laboratory training model with fresh cadaveric cow cranium, simulating standard microneurosurgical steps in interhemispheric-transcallosal approach to the lateral ventricle.The same authors also designed a training model in cadaveric sheep cranium, mimicking the steps of posterior fossa surgery in humans 14 .Both methods proved to be useful to refine skills and to provide more intimate knowledge on brain surgery to the neurosurgery residents.In our study, both procedures could be accomplished in the swine brain model.
Pig brain is comparable to human one in gross anatomy, histology and vascularization with some differences.The frontal lobe is less developed and the olfactory system occupies a large portion of the anterior part of the brain.A massive skull protects its brain with size and shape changes during the growth resulting in surgical intervention difficult 7 .The weight of the adult pig brain ranges from 80 to 180g, and can be comparable to the brain mass of several non-human primate species used for experimental purposes 15 .Therefore, it seems to be large enough to allow neurosurgical training.
Regelsberger et al. 8  Borucki et al. 17 evaluated the endoscopic anatomy of the cerebellopontine angle through the retrosigmoid approach in a swine specimen, and found analogy to human's anatomy.In our study, the cerebellopontine angle was exposed and drilling of the internal auditory canal, an important step in vestibular schwannoma surgery, could be accomplished.

Conclusion
The pig model provides an alternative and has great value for the acquisition and refinement of surgical skills.In addition, this model contributes to the reduction of live animals usage for surgical training
published a 4-years experience in an in vivo swine model for training neurosurgical residents.Surgical procedures included craniotomy, dural opening, brain surgery and excision of an artificial tumor created by injection of colored fibrin glue.The model has proved to be a great opportunity for young neurosurgeons to train bleeding management and surgical complications.Olabe et al. 16 developed a reproducible technique for aneurysm creation in domestic swine and adapted it to mimic intracranial dissection in an in vivo model.Several aneurysm clipping techniques, emergency rupture situations and vascular reconstruction procedures could be trained.