Application of 3D Printing Technology in Microvascular Decompression for Trigeminal Neuralgia via Retrosigmoid Craniotomy

Summary

This protocol evaluates the application of 3D printing technology in cranial microvascular decompression for trigeminal neuralgia via retrosigmoid craniotomy, with a focus on individualized image data import, image processing, 3D model fabrication, intraoperative surgical guidance, and postoperative outcomes.

Abstract

Retrosigmoid craniotomy is the preferred surgical approach for treating cerebellopontine angle (CPA) lesions, particularly for microvascular decompression in primary trigeminal neuralgia. However, inaccurate localization of the transverse-sigmoid sinus junction (TSSJ) often leads to postoperative complications. To address this issue, the E-3D digital medical modeling and design system was employed for preoperative visualization and localization of the TSSJ, enabling precise surgical planning. The E-3D software identified the optimal position for the strategic burr hole, visualized its spatial relationship with the sigmoid and transverse sinuses, and facilitated the creation of a 3D-printed surgical guide plate to assist intraoperative navigation. This protocol minimizes injury to the sigmoid and transverse sinuses, reduces the risk of excessive skull defects, and helps prevent postoperative complications such as cerebrospinal fluid (CSF) leakage and infection. Overall, the integration of 3D printing technology and surgical guide plates enhances the safety and precision of retrosigmoid craniotomy.

Introduction

The retrosigmoid craniotomy (RCS) is one of the most widely used surgical approaches for accessing the CPA. This technique offers several advantages, including ease of operation, clear exposure of the cerebellopontine angle structures, and the ability to open the internal auditory canal as needed while preserving the facial nerve, auditory nerve, and surrounding vasculature. As a result, RCS has become the preferred surgical approach for treating pathologies in the CPA region¹. However, during microvascular decompression via retrosigmoid craniotomy for trigeminal neuralgia, it is essential to fully expose the junction of the sigmoid and transverse sinuses, the inferior edge of the transverse sinus, and the medial border of the sigmoid sinus. This often requires extensive bone removal, which increases the risk of venous sinus injury, postoperative CSF leakage, and other complications^2,3,4. Traditionally, the 'strategic burr hole' is localized using the 'star point,' defined as the intersection of the parietal, occipital, and temporal bones posterior and superior to the mastoid root. This point corresponds to the external cranial projection of the transverse-sigmoid sinus junction⁵. However, due to anatomical variations among individuals, relying solely on the 'star point' for localization often results in inaccuracies, increasing the risk of sinus injury and potentially leading to severe complications^6,7.

With the rapid advancement of modern medical imaging, cranial Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) enable the acquisition of precise and individualized patient anatomical data. CT-based 3D reconstruction can transform two-dimensional images into three-dimensional models, facilitating preoperative localization of the 'strategic burr hole'⁸. However, it fails to directly visualize the relationship between the 'strategic burr hole' and lateral skull landmarks during surgery, limiting its utility for real-time surgical guidance. Intraoperative neuronavigation systems, based on MRI, can directly map the position and morphology of the transverse and sigmoid sinuses onto the scalp and skull surface, allowing for more accurate localization of the 'strategic burr hole'⁹. Nevertheless, these systems are complex to operate, costly, and prolong anesthesia and surgical duration. Additionally, most hospitals lack proficiency in this technology¹⁰. Therefore, identifying an economical, convenient, safe, and reliable method for designating the 'strategic burr hole' holds significant clinical importance.

In recent years, 3D printing technology has seen rapid development and increasing application in the medical field¹¹. This technology offers significant advantages for clinical use, as it can convert individualized CT and MRI imaging data into intuitive, tangible models for surgical guidance. Additionally, it is cost-effective, highly accurate, and easy to produce¹². In this study, we present the case of a 65-year-old female patient with trigeminal neuralgia who underwent microvascular decompression via retrosigmoid craniotomy, guided by preoperative and intraoperative 3D printing technology, as a representative case.

Protocol

The General Hospital of Ningxia Medical University approved the use of 3D printing to guide surgical procedures for the treatment of a 65-year-old patient with trigeminal neuralgia (KYLL-2025-1006). Written informed consent was obtained from the patient. The 3D printing supplies were commercially obtained. The reagents and equipment used in the study are listed in the Table of Materials.

1. Collection and recording of the patient's medical history

1. Communicate with the patient to assess the location of trigeminal neuralgia, frequency of attacks, pain characteristics, associated symptoms, and prior treatment history.
   NOTE: The primary clinical features of trigeminal neuralgia include: (1) Pain - recurrent, transient episodes of electric shock-like, stabbing, or tearing pain within the trigeminal nerve distribution area, characterized by sudden onset and abrupt cessation. (2) Frequency - pain is often triggered by specific actions, lasting from seconds to minutes, with symptom-free intervals between episodes. Severe cases may be accompanied by ipsilateral facial muscle spasms. (3) Associated symptoms - ipsilateral facial flushing, sweating, elevated skin temperature, pupil dilation, tearing, mucosal congestion, and increased salivation.

2. Pre-surgical examinations

1. Perform the physical examinations.
   NOTE: Physical examination includes: (1) Sensory Examination - assess facial skin sensation, including the sensory distribution of the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve. (2) Reflex Examination - evaluate the corneal reflex by gently sweeping a cotton wisp across the lateral aspect of the cornea. (3) Motor Examination - examine the function of the medial pterygoid, lateral pterygoid, masseter, and temporalis muscles. Observe symmetry and strength during mouth opening and closing.
2. Magnetic resonance imaging
   1. Perform MRI to identify primary and secondary trigeminal neuralgia (as shown in Figure 1).
      NOTE: Primary trigeminal neuralgia clearly shows the relationship of the trigeminal nerve to the peripheral vessels, as well as the alignment of the responsible vessels.
3. Computed tomography (CT) examination
   1. Perform CT to reconstruct skull images showing the morphology of the posterior fossa, the sigmoid and transverse sinuses, and the 'star point' on the lateral side of the skull (as shown in Figure 2).
4. Electrophysiological examination
   1. Perform preoperative electrophysiological examination to determine the type of trigeminal neuralgia.
      NOTE: Preoperative electrophysiological examination includes the following indicators: (1) Pain-related evoked potentials (PREP) - provides an objective assessment of nociceptive conduction pathways and is considered the gold standard in clinical neurophysiological evaluation of pain. (2) Current perception threshold (CPT) - represents the minimum stimulation intensity required to consistently elicit a sensory response at a specific frequency and test site. (3) Quantitative sensory testing (QST) - quantifies the stimulus intensity needed to evoke specific sensations, enabling functional assessment of thick myelinated, thin myelinated, and unmyelinated nerve fibers. (4) Blink reflex (BR) - a defensive reflex triggered by stimulation of the supraorbital nerve, periorbital percussion, corneal provocation, or acoustic/optical stimuli. (5) Masseter inhibitory reflex (MIR) - also referred to as exteroceptive inhibition, MIR is a protective mechanism that safeguards the teeth and jaw during occlusion and mastication.

3. 3D-printed surgical guide fabrication

1. Importing imaging data and exporting surgical guides
   1. Download the raw DICOM data of the patient's cranial CTA scan from the hospital PACS system.
   2. Use the E-3D Digital Medical Modeling and Design System to perform the following operations: import the DICOM data through the "Data Management - Import CT/MRI" module.
   3. After completing the 3D printing guide design, export the STL model to the 3D printer using the "Export STL Model" function.
2. Three-dimensional reconstruction of cranial anatomical structures
   1. Perform 1:1 scale multi-tissue reconstruction of the patient's craniofacial anatomy using the 3D reconstruction module using the compatible software, including precise segmentation of the skin, sigmoid sinus, transverse sinus, and cranial bone structures (as shown in Figure 3).
      NOTE: After completing the three-dimensional reconstruction of the sigmoid sinus and transverse sinus, digital trimming was used to clearly display the morphology of the vascular sinuses and the three-dimensional spatial structure of the junction between the sigmoid sinus and transverse sinus. The cranial bone model was reconstructed by cutting along the mid-sagittal plane to display the ipsilateral sigmoid sinus groove and transverse sinus groove, verifying the spatial relationship between the reconstructed vascular sinuses and the corresponding grooves.
3. 'Strategic burr hole' positioning and surgical pathway planning
   1. Perform precise surgical planning using the software's trajectory planning module to designate the 'Strategic Burr Hole' at the intersection of the reconstructed sigmoid sinus and transverse sinus.
   2. Simultaneously display axial, coronal, and sagittal CT images and adjust the nail path trajectory in real-time (as shown in Figure 4).
      NOTE: The reconstructed 3D image shows the nail path, and the intersection of the nail path and the skull is the 'Strategic burr hole', which also serves as the visual marker point for methylene blue on the outer plate of the skull.
4. Preparation of personalized surgical guides
   1. Utilize the universal guide plate design function in thre software. Select craniofacial anatomical landmarks (zygomatic arch, nasal root, and 'Strategic burr hole') and merge them with the nail track trajectory to form a surgical guide plate.
   2. Implement the path extraction → base surface generation → guide plate fusion algorithm to create a patient-specific guide plate model with integrated navigation channels.
   3. Export the finalized guide plate model as per step 3.1 and manufacture using 3D printing technology (Figure 5).
      NOTE: E-3D software can automatically combine marked anatomical regions with preset nail paths to form a guide plate model with channels (Figure 6).

4. Surgical procedure

1. Use the 3D-printed surgical guide plate to accurately position the 'strategic burr hole'. After positioning the patient and fixing the head frame, place the sterile surgical guide on the head and face according to anatomical landmarks to precisely locate the 'strategic burr hole' (Figure 7).
   NOTE: Using a 5 mL syringe, penetrate the scalp along the preset nail track trajectory of the guide plate to reach the outer surface of the skull, and inject 0.05 mL of 1% methylene blue. The bone surface marking points formed by methylene blue correspond to the pre-planned 'strategic burr hole'.
2. Confirmation of the accuracy of surgical guides
   1. Incise the skin and subcutaneous tissue. Identify the methylene blue-marked area on the outer surface of the skull. Drill at this location, then verify whether its outer edge corresponds to a vascular sinus (Figure 7).

5. Postoperative care

1. Closely monitor mental status, level of consciousness, and vital signs. Implement fluid management to prevent low intracranial pressure. Perform a cranial CT scan 2 h postoperatively (as shown in Figure 8).
   NOTE: Postoperatively, symptoms resolved completely, with no recurrence of percussion-induced trigger point pain.

Results

All patients were diagnosed with primary trigeminal neuralgia, and multiple sclerosis was excluded. Clinical examination revealed the involvement of the maxillary branch of the ipsilateral trigeminal nerve and, to a lesser extent, the mandibular branch. The pain was characterized by an electric shock-like quality and could be triggered by activities such as toothbrushing or tapping on the trigger points. The duration of pain episodes varied, and no abnormalities in corneal reflexes or facial motor function were observed....

Discussion

Retrosigmoid craniotomy is the preferred surgical approach for microvascular decompression (MVD) in trigeminal neuralgia, requiring adequate exposure of the sigmoid sinus and transverse sinus junction¹³. After CSF drainage, the cerebellum is retracted using the angle between the cerebellar vermis and the petrous bone to expose the CPA region. Lesions in the CPA region include, but are not limited to, trigeminal neuralgia, acoustic neuromas, cholesteatomas, trigeminal nerve sheath tumors, and facia...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3D printing supplies	Zhongshan Dajian Technology Co.	UTR8360X
Cranial stabilization & Brain retraction	Mayfield Ltd.	A2000
CT	Siemens Medical Systems Ltd.	SOMATOM Force
E-3Ddigital medical modeling and design system	Hunan Liuwei Jinghang Digital Technology Co., Ltd.	(x64 V19.12 version)
Gauze	Yixin Medical Equipment Co.
Iodophor	Shandong Lilkang Medical Technology Co.
Medtronic IPCTM	Medtronic Medical Devices Ltd.
Methylene Blue Injection	Jumpcan PhaJumpcan Pharmaceutical Group Co., Ltd
MRI	Siemens Medical Systems Ltd.	MAGNETOM Vida
Surgical blades	Shanghai Pudong Jinhuan Medical Supplies Co.
Syringe	Hunan Oasis Huikang Development Co.
Tampon	Henan Zhongjian Medical Equipment Co.
UnionTech 3D printer	Shanghai Luen Thai Science & Technology Co.	Lite 600