Chapter 1: Equipment Requirement for Temporal Bone Dissection

Equipment Requirement for Temporal Bone Dissection

Introduction

Temporal bone preparation requires instruments similar to those used in middle ear surgery. A streamlined, high-quality instrument set is essential for ensuring precise and effective dissection. This set typically includes various forceps, a sickle knife, straight and angled round elevators, a needle, a micro perforator, a 0.6-mm angled hook, curettes, and diamond and cutting burrs of different sizes. Specialized tools for specific procedures can be provided by the instructor as needed. Suction and irrigation systems are indispensable components (2).

Essential Surgical Instrumentation

To replicate live surgical procedures during temporal bone dissection, a comprehensive set of tools is required. The following instruments are recommended to facilitate a realistic and efficient dissection experience (3, 5):

• Microscope: A high-quality microscope is vital for magnification and precision.
• Micromotor: A non-sterilizable micromotor equipped with cutting burrs (1 – 7 mm) and diamond burrs (1 – 7 mm) for drilling and polishing.
• Suction and Irrigation Systems: Suction tubes and suction irrigation systems of various sizes to maintain a clear surgical field.
• Surgical Knives and Scalpels: Bard Parker’s knife with No. 15 and No. 22 blades are essential for making precise incisions.
• Scissors: Includes tissue and microsurgery scissors for delicate cutting.
• Elevators and Dissectors: A complete set comprising Lempert periosteal elevators, Freer elevators, straight dissectors (Parabeug), round dissectors (both right-angled and straight), fine dissector hooks, and needles.
• Retractors: Self-retaining retractors for consistent exposure of the surgical area.
• Rongeurs: Used for bone removal and shaping.
• Specialized Tools: Annulus elevators, gently curved picks (e.g., Rosen needles), and malleus snipers for precise handling of bone and soft tissues.

Preparation and Planning

Ensure a comfortable sitting position to minimize fatigue during dissection. Stabilize your hands on the table or specimen holder for better control, especially during delicate manipulations. Ideally, work with fresh or fresh-frozen temporal bones instead of air-dried or formalin-fixed specimens. Employ safety protocols, including gloves, gowns, and eye protection, to mitigate risks (2).

Clean the temporal bone by removing connective tissues and secure it in a temporal bone holder oriented as in surgical practice. Identify key anatomical structures and landmarks, such as the lateral sinus and jugular bulb, which can vary significantly based on the degree of pneumatization. Beginners are advised to avoid sclerotic specimens, as their landmarks may be less discernible (2).

The mastoid preparation progresses through steps like antrostomy and mastoidectomy, followed by identifying the semicircular canals and the descending facial nerve. Additional procedures like facial nerve decompression, posterior tympanotomy, and cochleostomy are undertaken before approaching the internal auditory canal (IAC) through sacotomy or labyrinthectomy (2).

For ossicular chain reconstruction, conduct exercises before removing the posterior meatal wall to form a mastoid cavity. Retain removed ossicles for reconstruction practice, as the external ear canal’s rigidity differs from in vivo conditions. A substantial portion of the meatal skin may need removal to facilitate access (2).

Specimen Preparation

Freshly preserved bones in formalin are preferred, as older specimens often exhibit discoloration and obliterated vessels filled with hard coagula. Immerse bones in water for two hours to reduce formalin odors and prevent tissue desiccation overnight, which can lead to fragility and altered color (3).

The injection technique developed by Dr. M. Landolfi involves identifying the internal jugular vein and internal carotid artery in the neck. These vessels are thoroughly rinsed with tap water to clear coagula before injecting colored silicone. For cadaver heads, inject silicone into the transverse sinus, internal carotid artery, and external carotid artery. Allow the silicone to set before beginning dissection (3).

General and Soft Tissue Preparation

Temporal bones should be positioned in a surgical orientation, with the posterior aspect facing the surgeon and the temporomandibular joint directed away. Trim excess bone from the squama to ensure the specimen fits securely in the holder. Retain the external ear initially to perform meatoplasty within a closed cavity. Following meatoplasty or in cases where the pinna is absent, transect the external canal approximately 2 cm lateral to the bony-cartilaginous junction (7).

For soft tissue preparation, rinse the bone in water and determine whether it is right- or left-sided. Remove excess soft tissue and periosteum using scalpels and periosteal elevators. Avoid damaging deep meatal skin. Note the relative position of the external auditory meatus (EAM) to the temporomandibular joint and document tissue thickness across meatal walls (7).

General Rules and Safety

Specimens should be taken out of refrigeration an hour before dissection. Ensure all required instruments, such as the drill, are operational and conduct a quick anatomy review. Use labeled plastic bags to store specimens securely. Maintain proper sanitary protocols, including anti-hepatitis vaccinations, and use personal protective equipment to avoid inhalation of bone dust or eye injuries. Dispose of bone remnants and dust as medical waste and leave the workspace clean for subsequent users (9).

Microscope Setup and Use in Temporal Bone Surgery

Preparing the Microscope

Begin by ensuring the microscope is balanced and easy to manoeuvre. Familiarize yourself with its mobility and make initial adjustments at a lower magnification to gain a broader view. Confirm binocular stereoscopic vision by adjusting the position of the eyepieces. Proper alignment ensures comfort and accuracy during prolonged use (2).

Effective Use of the Surgical Microscope

The surgical microscope is an indispensable tool in temporal bone surgery, where precision is critical. Mastery of its use requires practice and careful adjustment to achieve three-dimensional visualization, enhanced lighting, and detailed imaging. Over time, the microscope will become an extension of your vision, facilitating microsurgical techniques with sub-millimeter accuracy (5).

Key Adjustments:

• Eyepiece Spacing: Set the interocular distance to ensure a single fused image. Record this distance for future reference to maintain consistency.
• Focus Settings: Adjust eyepieces to ensure both eyes remain comfortably focused across magnification levels. For those with mild refractive errors, the microscope’s enhanced lighting and magnification may negate the need for eyeglasses. However, if a strong prescription is required, wear glasses and set the eyepiece adjustments to zero, retracting the rubber surrounds for better fit.

Adjusting for Parfocal Vision

To optimize the microscope for parfocality, follow these steps (4):

1. Draw a small cross (+) on white paper as a focusing target.
2. Set both eyepiece diopter adjustments to zero (0).
3. Focus on the target using maximum magnification with your right eye, ensuring the microscope remains stable by lightly tightening tension knobs.
4. Close your right eye and adjust the left eyepiece until the image is clear. Lock the diopters once the adjustment is complete.
5. Adjust the interpupillary distance so the circular light images from both eyepieces converge into one.
6. Confirm parfocality by rotating the magnification changer through its settings while keeping the target in focus.

Strategic Magnification Usage

Effective dissection requires dynamic adjustments to magnification, depending on the task:

• Low Magnification: Provides a broad overview, aiding in the exposure of spaces while preserving depth perception to prevent injury to deeper structures.
• High Magnification: Necessary for intricate work on specific structures, such as the stapes footplate, nerves, or vessels.

While learning, rely on lower magnification to avoid inefficiencies caused by excessive focus on fine details. As proficiency develops, magnification can be adjusted more strategically to align with the surgical stage and objective.

Drills and Burrs: Preparation and Usage in Temporal Bone Surgery

Testing and Preparation of the Drill

Before working on bone, thoroughly test the drill to ensure safety and functionality. Securely fix the drill to the handpiece and select an appropriate burr based on anatomical requirements, starting with a larger burr for initial bone removal. Confirm that the drill rotates clockwise for maximum efficiency with cutting burrs. Approach the bone surface with a rotating burr, applying moderate pressure and operating at speeds between 20,000–40,000 RPM. Adequate irrigation is essential to prevent thermal damage to the bone (2, 7).

Sharp burrs are crucial for precise work and efficient time management. Blunt burrs can cause unnecessary delays and may slip, risking trauma to delicate structures. Begin with a large burr to expedite bone removal and minimize the risk of perforating the dura or damaging critical structures like the facial nerve or labyrinth (2).

Drilling Techniques and Safety

Continuous irrigation during drilling helps to clear bone dust and connective tissue from the drill, reducing the risk of overheating. Pay attention to variations in bone resistance and density, as these changes will produce distinct tactile feedback and sound.

When working near vulnerable structures, such as the labyrinth or facial nerve, use diamond burrs to reduce the likelihood of damage. Always drill parallel to critical structures, avoiding perpendicular approaches. Rest the hand holding the drill on the specimen or the supporting bowl for better control, as both sides of the drill can potentially cause harm (2, 4).

Types of Burrs and Their Applications

Burrs are categorized into cutting and diamond types:

• Cutting Burrs: Made of tungsten carbide or stainless steel. Stainless steel burrs are suitable for dissection, while tungsten carbide burrs are preferred for surgical procedures due to their efficiency and durability (4).
• Diamond Burrs: Best suited for work near sensitive anatomical areas, providing finer control and reduced risk of trauma (4).

Burr sizes typically range from 3–6 mm for cutting burrs and 2–4 mm for diamond burrs. The appropriate size should be selected based on the stage and precision required during the procedure (5).

Handling and Maintenance of the Drill

To fix a burr, unlock the handpiece, insert the burr, and then lock it securely. Regular maintenance, including oiling the handpiece (but not the motor system), is necessary for smooth operation. After each session, remove burrs from the handpiece, clean their teeth with a scalpel tip or small wire brush, and wipe the handpiece clean. Lubricate the handpiece as needed to ensure optimal functionality (7).

Control the drill speed using the foot switch, as tabletop controls for speed and reversing are typically unnecessary during standard procedures. Proper handling and maintenance will extend the longevity of the instrument and ensure its effectiveness (7).

This rewrite integrates all relevant points into a cohesive format, providing practical guidance for a master’s-level audience while maintaining proper citations. Let me know if further refinement is needed!

Temporal Bone Holder

For effective dissection in a temporal bone laboratory, specimens are secured using a House–Urban temporal bone holder. For half-head preparations required in skull base approaches, a custom-designed temporal bone holder is employed. This holder features a larger diameter and is equipped with five fixing rods, making it ideal for accommodating larger specimens (3).

Suction Irrigation: Best Practices in Otologic and Neuro-Otologic Surgery

Importance of Suction Irrigation

Suction irrigation is a critical tool in otologic and neuro-otologic procedures. It effectively removes bone dust that can obstruct the surgical field and accumulate between the flukes of the burr, reducing its sharpness. Additionally, suction irrigation cools the drilling surface, preventing thermal damage to adjacent structures. This is particularly essential during procedures such as identifying the facial nerve or blue-lining a semicircular canal, where precision is paramount (3).

Technique for Effective Use

When using a suction irrigator, avoid holding it steady while burring. Instead, move it around the burr to optimize dust removal and cooling. A practical approach is to position the suction tip between the burr and a critical structure. This technique acts as a safeguard, ensuring that if the burr slips, it impacts the suction tip rather than damaging the exposed structure (3).

Specialized Equipment

For neuro-otologic work, particularly in the cerebellopontine angle, the Brackmann suction tip is recommended. This tip is designed with a blunt end and side holes to minimize direct suction force on neurovascular structures, enhancing safety during delicate procedures (3).

Operational Checks

Before surgery, ensure that the suction system is functional, and the collection bottle is not full. Suction pressure should be maintained at approximately 400 mm Hg when the tube is occluded to provide optimal performance (7).