40 Training in Skull Base Surgery

• The role of residency and fellowships is of paramount importance. Imitation of senior surgeons is the most powerful method by which surgeons learn to operate.1 A stepwise educational progression undertaken by surgical residents provides better surgical outcomes with lower morbidity.^{2, 3}

• Skull base surgery has a particularly steep learning curve, and the skull base surgeon has to master both endoscopic and microscopic techniques.

Anatomy Lab

• Cadaver dissection in the anatomy lab enables trainees to acquire a practical knowledge of surgical anatomy, giving them the chance to improve their dissecting and surgical techniques.^4,5

• Laboratory training is imperative to acquire expertise in microsurgical techniques (as emphasized by Yasargil)⁶ and endoscopic techniques.⁴

• A cadaver lab is the place where beginners can learn and train, experts can test their skills, and good surgeons can become better surgeons.⁴

• The training checklist in the anatomy lab is as follows⁴:

1. Manual training

2. Anatomy orientation

3. Simulation surgery

• Developing the ability to handle different instruments, such as endoscopes and microscopes, including those provided with angled endoscopes, and learning three-dimensional (3D) anatomy orientation are important goals of trainees in the lab. Angled endoscopes increase the ability to view structures “around the corner,” but they also increase the risk of disorientation.7 The combined use of endoscopes and microscopes provides different points of view of the same object at the gross, mesoscopic, and surgical microscopic levels.⁸

• The cadaver lab can be used for simulating the surgical approach and testing its feasibility. Novel approaches should seek to be minimally traumatic rather than minimally invasive.⁴

• In the cadaver lab, it is possible to analyze the ergonomics of the setting and the instrumentation⁹ by testing drills, aspirators, ultrasonic aspirators, and aneurysms clips, and by studying the position of the monitors and tools to ensure an optimal setup in the operating room.⁴

• Surgical techniques and approaches for removing mass lesions may be tested using skull base tumor models. By using resin polymer injections (the resin can be injected via the endonasal route in different locations), it is possible to simulate a skull base tumor and its surgical resection.¹⁰

• Anaglyphic 3D stereoscopic printing is a relatively easy technique for 3D prints of anatomic structures.^11,12

• In mastoidectomy training, the drilling of the bone can be performed after injection of indocyanine green in the arteries of the cadaver, which enables fluorescence-guided bone drilling. Techniques such as skeletonization of the facial nerve and semicircular canals can then be practiced.¹³ The indocyanine diffuses into the more vascularized regions, such as the mucosa covering the mastoid air cells, so that the fluorescent zone can be safely drilled, while the nonfluorescent regions indicate solid bone, such as the one covering the facial and the semicircular canals.

• Inexpensive and ultraportable systems for laboratory training in skull base endoscopic dissections have been developed. These systems cost a fraction of a standard high-definition endoscopy system.¹⁴

• For institutions with more resources, the lab can be equipped with radiological imaging tools (neuronavigation, C-arm fluoroscopy, computed tomography [CT]), surgical robots, 3D endoscopes, exoscopes, and others.

• Recording of anatomy dissections (photographs and videos) is useful for didactic purposes and training. Trainees may review their performance and implement changes to enhance their technical skills.

• A modular/incremental approach to endonasal skull base surgery is useful in endoscopy training.

• These levels of difficulty that can be mastered using cadavers are based on related surgical procedures of increasing complexity7,15–17:

1. Ligation of the sphenopalatine artery, endoscopic sphenoethmoidectomy, exposure of the nasofrontal recess.

2. Frontal sinusotomy and management of intrasellar region, as well as medial orbital decompression. In surgery, this level is often used for the resection of pituitary tumors, cerebrospinal fluid (CSF) leak repair, and surgical decompression of the optic nerve in Graves’ disease.

3. Extrasellar region; extended approaches to the clivus, odontoid, and petrous apex.

4. Extended approach to the planum, exposure of the internal carotid artery, intradural approach to the odontoid process, approaches to the parapharyngeal space, and craniofacial resection.

5. Approach to the circle of Willis and cranial nerves.

• Fresh/frozen specimens rather than skulls or formaldehyde-fixed specimens are the most realistic specimens for anatomic dissection and surgical training, although they are not readily available in many institutions. They may also carry risks of infections, and their use is limited to a short timeframe.

• Dried skulls can be used for simulation of craniotomies/craniectomies, petrosectomy, etc.

• Fixation enables preserving specimens for long periods of time. Formaldehyde-based embalming is the most commonly used technique for specimen preservation. Fixation in formaldehyde, however, does render the tissue quite tough and rigid. The use of fabric softener (methyl bis[tallow amido ethyl] 2-hydroxyethyl ammonium methyl sulfate) has been proposed for softening the tissue following formaldehyde fixation and obtaining ideal tissue texture.¹⁸ Otherwise, a customized formula made of ethanol (62.4%), glycerol (17%), phenol (10.2%), formaldehyde (2.3%), and water (8.1%) has been shown to prevent decay of the specimen, giving the brain a consistency very similar to that of tissues obtained in cryopreserved specimens.¹⁹

• Blood vessels of specimens can be injected with colored silicone rubber (e.g., red for the arteries and blue for the veins), latex, and other solutions.^20,21 The injection of blood vessels can be performed via the cannulation of the carotid and vertebral arteries at the neck, as well as the jugular veins, whenever required. Arterial injections are generally considered to be enough for most approaches, but this depends on the anatomic target; dissection of the orbits, pineal gland, and cavernous sinus, for example, also requires venous injection. Latex injections result in deeper penetration of the solution into small cerebral vessels than silicone,21 although the latter makes the vessels softer for surgical manipulation.

• Pressurized dynamic filling of the cerebral vasculature and subarachnoid cisterns makes the anatomic dissection an experience very similar to actual surgery on patients.^{22, 23}

• Lack of perfusion and in vivo elasticity may be compensated for by introducing animal training, as in in-vivo swine models²⁴ or anesthetized rats. The latter can be used especially for bypass surgery training.

• Plastination techniques give persistently dry, odorless and durable specimens, which can also be used for skull base anatomy training.^25,26 The rigidity of the specimens typically only allows for training on rigid structures, such as the petrous bone, rather than on soft parenchyma, such as the brain. Despite these limitations, plastination remains a fascinating technique for preserving organs and learning anatomy (especially plastinated slices of anatomic regions, such as brain slices in all axes).^27,28

Artificial Models

To address a potential lack of cadavers and animal models, 3D plastic models have been developed for microsurgery and endoscopy training, including suturing, performing duraplasty and cranioplasty, and other procedures.^30–36

Related posts:

Pearls of Skull Base Meningioma Surgery Craniovertebral Junction Functional Anatomy of the Cranial Nerves Skull Base Infections Skull Base Reconstruction Techniques Transcranial Approaches to the Skull Base

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