Development of a Cadaveric Multiport Model of Posterior Circulation Aneurysm Clipping for Neurosurgery and Otolaryngology Residents

Summary

A model protocol to train neurosurgery and otolaryngology resident learners on endoscopic transclival clipping of posterior circulation aneurysms is described. Two endoscopic approaches to access the silicone-injected or perfused posterior circulation of cadaveric heads are established for training. Learners are tasked with clipping of posterior circulation based on clinical scenarios.

Abstract

Posterior circulation aneurysms are difficult to treat with the current methods of coiling and clipping. To address limitations in training, we developed a cadaveric model to train learners on endoscopic clipping of posterior circulation aneurysms. An endoscopic transclival approach (ETA) and a transorbital precaruncular approach (TOPA) to successfully access and clip aneurysms of the posterior circulation are described. The model has flexibility in that a colored silicone compound can be injected into the cadaveric vessels for the purpose of training learners on vascular anatomy. The other option is that the model could be connected to a vascular perfusion pump allowing real-time appreciation of a pulsatile or ruptured aneurysm. This cadaveric model is the first of its kind for training of endoscopic clipping of posterior circulation aneurysms. Learners will develop proficiency in endoscopic skills, appropriate dissection, and appreciation for relative anatomy while developing an algorithm that can be employed in a real operative arena. Going forward, various clinical scenarios can be developed to enhance the realism, allow learners from different specialties to work together, and emphasize the importance of teamwork and effective communication.

Introduction

Treatment of posterior circulation aneurysms presents unique challenges and has higher complication rates compared to other cerebral aneurysms¹. Transcranial clipping of posterior circulation aneurysms is technically challenging, with high complication rates and morbidity². Endovascular coiling and endoscopic endonasal surgery are safe alternatives, as they reduce complication rates and limit traction on the cerebrum³. Endovascular coiling has been shown to have benefits over open skull base approaches, and most centers now use an endovascular approach to treat cerebral aneurysms⁴. However, many posterior circulation aneurysms are not amenable to coiling due to the location, vessel tortuosity, and vessel size². Recent studies have shown the feasibility of using endoscopic approaches for the clipping of posterior circulation aneurysms^5,6,7,8.

Although endoscopic endonasal surgery has demonstrated benefits over more invasive procedures, several studies document a learning curve associated with the use of endoscopic equipment^9,10,11. It is this learning curve and lack of surgeon training and experience that limit the use of this safe and beneficial treatment option³. As endoscopic clipping for aneurysms is revealing itself to be a feasible and a safe treatment course, neurosurgery and otolaryngology residents will need to develop these surgical skill sets during their training. This need for technical skill combined with a steep learning curve necessitates the development of realistic training models, as several repetitions are needed to reduce operative room time and complication rate in endoscopic endonasal surgery^9,11. In a human placental model of cerebral aneurysm clipping, Belykh et al. have demonstrated improvement in the use of aneurysm clip applicators in learners after simulation¹². Similarly, training with 3-dimensional printed models has been shown to improve learner technical skills in aneurysm clipping¹³. As with any training model, cost-effectiveness and reproducibility are leading objectives for wider accessibility. We have previously demonstrated the utility of an ETA and a TOPA in a cadaver model of posterior circulation aneurysm clipping, with approach access and visualization affected by clip location¹⁴. TOPA can be used in conjunction with endoscopic endonasal approaches, and has previously demonstrated shorter working distances, improved visualization, and angles resulting in increased access to structures^4,14. The TOPA procedure is a new approach for clip ligation of aneurysms, and its applicability can be further explored via simulation for access to both tumors and aneurysms. In this protocol, we present the steps for development of a realistic, cost-effective, reproducible posterior circulation aneurysm-clipping model using ETA and TOPA as options to train neurosurgery learners. An advantage of our model is learner's exposure to authentic physical anatomy, with the option to incorporate realistic dynamic bleeding in the training of aneurysm clipping. This model can be set up with a static (silicone compound infused) or a dynamic (perfused) anatomy and is applicable to train neurosurgery or otolaryngology learners at various levels of expertise on the anatomy and management of posterior circulation aneurysms.

Protocol

In the development of this model, three cadaveric heads were obtained through the Oregon Health & Science University Body Donation Program and handled per the Code of Ethics approved by the Oregon Health & Science University Institutional Review Board.

1. Head Preparation

1. Obtain fresh cadaveric heads. Secure the head in the sink, resting on a block with the neck facing upwards.
2. Prepare a 5 L 1:100 solution of anticoagulant citrate dextrose and warm water. Use the solution within 72 h.
3. Insert a 5-mm arterial cannula into the right jugular vein (lateral to carotid) and apply an arterial cannula clamp around the vessel. Perfuse the vessel for 15 min with a perfusion pump and anticoagulant citrate dextrose solution to wash the vessel. Remove the cannula and repeat with the left jugular vein and carotid arteries bilaterally. Repeat with a 3-mm cannula on the vertebral arteries bilaterally.
4. Allow the heads to sit and dry overnight. Position the heads with the face facing upwards and neck positioned at a 45 ° angle with a supporting block underneath. Then store in a cold room at 5 °C overnight.
5. Embed the heads in 2 L of embalming solution. Store heads in a bucket, submerged in 10% formalin fixative solution.
6. Use the prepared heads with either silicone compound injections to train with static anatomy (step 2) or arterial injury and perfusion setup to train with dynamic anatomy (step 4).
   1. To complete the silicone compound injections (step 2): complete step 2, then move to step 3 to complete the dissection.
   2. To complete the arterial injury and perfusion setup (step 4): complete the step 3 dissection, then move to step 4 for perfusion instructions.

2. Silicone Compound Injections

1. Prepare the silicone compound solution according to the manufacturer's instructions (50 µL diluent, 40 µL red silicone compound dye, and 4.5 µL curative agent).
2. Use dissection to identify the external carotid arteries. Clamp the right external carotid artery with a hemostat to focus the injection into the intracerebral vasculature.
3. Insert the arterial cannula into the right internal carotid artery and apply the arterial cannula clamp around the vessel. Inject 20 µL of silicone compound solution. Stop the injection when the flow of the silicone compound solution is noted at the left common carotid artery.
4. Clamp the common carotid arteries bilaterally with hemostats.
5. Insert an arterial cannula into the right vertebral artery and apply an arterial cannula clamp around the vessel. Inject 10 µL of silicone compound solution. Stop the injection when the flow of silicone compound solution is noted at the left vertebral artery.
6. Clamp the vertebral arteries bilaterally with hemostats.
7. Allow the head to sit at room temperature for 30 min, then gently remove all clamps.

3. Tissue Dissection

1. Position heads with the face upwards and the neck positioned at a 45° angle with a block positioned beneath it in order to visualize the nasal passages.
2. Obtain 0- and 30-degree endoscopes of 4 mm diameter and 18 cm length. Connect it to a fiber optic camera and a light source.
3. Prepare all heads with both ETA and TOPA dissections.
4. ETA ¹⁴ :
   NOTE: See Figure 1A for representation of the ETA dissection.
   1. Use a speculum to move the middle turbinates laterally on bilateral sides.
   2. Use suction and a Penfield 1 dissector to identify the sphenoid ostium bilaterally.
   3. With an 11-blade knife, make an incision on the right side of the nasal septum at the articulation of the sphenoid rostrum and vomer to bone. Make the incision 1 cm below the cribriform plate and to the floor of the nasal cavity.
   4. Dissect the mucoperiosteum from the bone using a Penfield 1 dissector.
   5. Disarticulate the sphenoid rostrum from the bony nasal septum with a Penfield 1 dissector and perform septectomy.
   6. Use a Kerrison 2 to cut the bone from the sphenoid ostia to the floor of the sphenoid sinus bilaterally.
   7. Grasp and remove the keel with a large pituitary rongeur to expose the sphenoid sinus, and remove mucosa.
   8. Use a trans sphenoidal drill to drill the remaining inferior rostrum of the sphenoid flush with the floor of the sphenoid sinus.
   9. Identify the bony impressions of the cavernous carotid arteries, opticocarotid recess, sella, and clivus (Figure 2); drill the clivus to expose its dura.
   10. Retract the pituitary gland (which should be in clear view) and drill out the clivus using a 5-mm coarse diamond burr.
   11. Remove the posterior clinoid.
   12. Dissect the lateral pituitary gland dura free from the pituitary gland; it is not necessary to dissect the dura over the pituitary gland.
       NOTE: If any inadvertent pituitary gland dura dissection occurs, it will not impact the function of the model.
   13. Use a Kerrison to remove bone fragments to expose the clival dura.
   14. Excise the clival dura to expose the basilar artery, anterior inferior cerebellar arteries (AICA), superior cerebellar arteries (SCA), and posterior cerebral arteries (PCA) (overview in Figure 3, anatomy detailed in Figure 4).
       NOTE: The clival dura may be retracted with a U-based flap and stabilized with a 2-0 silk suture.
5. TOPA ¹⁴ :
   ​Note: See Figure 1B for representation of the TOPA dissection.
   1. Move the caruncle laterally using forceps, then use scissors to make an incision medial to the caruncle where the conjunctiva meets the skin.
   2. Use iris scissors to widen the incision superiorly and inferiorly: the incision should continue behind the superior and inferior limbs of the medial canthal tendon; perform blunt dissection along the posterior limb of the medial canthal tendon to the posterior lacrimal crest.
   3. Use a Penfield 1 dissector to make an incision in the periosteum posterior to the lacrimal crest.
   4. Lift the periosteum from the medial orbit wall; continue to lift the periosteum toward the orbit apex in the subperiosteal plane.
   5. Identify and divide the anterior and posterior ethmoid arteries along the fronto-ethmoidal suture.
   6. Infracture the lamina papyracea between the ethmoid arteries and below the fronto-ethmoid suture with gradual pressure from a joker.
   7. Use a pituitary rongeur to remove bone in order to expose the sella, clivus, contralateral opticocarotid recess, and cavernous carotid arteries.

4. Arterial Injury & Perfusion Setup

1. Prepare arterial injury.
   1. Use an endoscope to visualize the anatomy of the posterior circulation (representation in Figure 3 and Figure 4).
   2. Select the location for the desired bleeding. For possible locations for simulated aneurysm bleed see Figure 5. Make a 3-mm laceration in the desired artery.
2. Perfusion setup & bleeding
   1. Cannulate the common carotid artery and secure with a clamp. Connect the cannula to the perfusion pump.
   2. Prepare artificial blood with a 3:1 ratio of water to commercially purchased fake blood. Then add 2 drops of red coloring for every 250 mL of water.
      NOTE: Prepared artificial blood may be reused for multiple simulations. 3 L of blood is prepared for each cadaveric head prior to the start of the simulation. This can be stored at room temperature. Shake before use.
   3. Start the perfusion pump and measure the mean arterial pressure (MAP) delivered to the cadaver head via an arterial line transducer and vital signs monitor. Maintain MAPs within a range of 65-110 mmHg to produce realistic bleeding depending on the desired simulation scenario.

5. Clip Placement in Simulation Training

1. Use an aneurysm clip and clip applier for vessel clipping in this model (Figure 6).
2. Use a clip applicator for clip placement (Video 1) at the simulated aneurysm sites of the posterior circulation (Figure 5).

Results

This model presents learners with multiple clinically-relevant sites for posterior circulation clipping, with either static (silicone compound-injected) or dynamic (perfused) options for training. Once dissection is complete, the investigators may use ETA and TOPA to provide learners with improved visualization of the posterior circulation¹⁴. Overview of ETA and TOPA are illustrated in Figure 1. For success of the model, investigators ...

Discussion

Posterior circulation aneurysms have been historically hard to clip or coil, especially those originating off the SCA and AICA. Several techniques have been tried, such as endovascular pipeline embolization devices, microsurgical skull base approaches, and the supraorbital keyhole approach for clip application^15,16,17. While these techniques are successful in some cases, the widespread applicability is limited due to stark diffe...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anticoagulant citrate dextrose	Pierce Laboratories	117037
Embalming solution	Chemisphere
10% Formalin fixative	Chemisphere	B2915DR55
Red Microfil solution	Flow Tech	MV-130	Silicone compound
Arterial cannula clamp
5 mm Arterial cannula	Instrument Design & Mfg. Co.	ART187-2-CT	Used for jugular vein and carotid artery cannulation
3 mm Arterial cannula	Instrument Design & Mfg. Co.		Used for vertebral artery cannulation
Curved hemostat	Aesculap	BH139R
Zero-degree endoscope (4 mm diameter, 18 cm length)	Karl Storz	H3-Z TH100
30-degree endoscope (4 mm diameter, 18 cm length)	Karl Storz
Suction - 7 and 10 FR	V. Mueller
11-blade surgical blade	Bard-Parker	371111
Penfield 1	Jarit	285-365
Kerrison rongeur	Aesculap	FM823R, 3mm/180 mm
Pituitary rongeur	Aesculap	FF806R
Transsphenoidal drill	Depuy-Synthes
5 mm coarse diamond burr drill	Depuy-Synthes
Forceps	Jarit	Carb bite I22-500
Iris scissors	Black & Black	B 66110
Perfusion Pump	Belmont Instrument Corporation, Billerica, MA, USA	Belmont Fluid Management System 2000
L-aneurysm clip	Peter Lazic Microsurgical Innovations	45.782
Vessel clip system	Peter Lazic Microsurgical Innovations	45.442
Dural flap clip	Weck	523242