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. Preoperative MRI ruled out secondary trigeminal neuralgia, and trigeminal vascular scans (Figure 1) identified the superior cerebellar artery and anterior inferior cerebellar artery as the causative vessels (Table 1). These findings were corroborated by preoperative electrophysiological studies, which confirmed the affected trigeminal nerve branches. Cranial CT imaging (Figure 2) demonstrated a well-developed posterior cranial fossa without malformations or intracranial hemorrhage, indicating no contraindications for surgery. Collectively, these findings confirm a definitive diagnosis of primary trigeminal neuralgia and establish the patient as a suitable candidate for 3D printing-guided microvascular decompression via a retrosigmoid craniotomy approach.

The position of the 'strategic burr hole' was visualized and designed based on the patient's preoperative examination data, and a 3D-printed surgical guide was fabricated (as shown in Figure 6). Preoperative patient positioning and routine sterilization of the surgical site were performed. Subsequently, under the guidance of a 3D-printed surgical template, methylene blue was marked on the lateral aspect of the skull. After drilling, the edges of the vascular sinus were visible through the 'strategic burr hole', confirming the accuracy of the preoperative positioning of the 'strategic burr hole' (as shown in Figure 7).

Figure 1: Preoperative MRI imaging of the trigeminal nerve. (A) Axial 3D-TOF-MRA image demonstrates a high-intensity vascular structure adjacent to the right trigeminal nerve. (B) Axial 3D-T2-weighted image provides clear visualization of the trigeminal nerve (scale bar: 1 cm). (C,D) Different levels illustrate the spatial relationship between the trigeminal nerve and surrounding vasculature, as well as the morphological features of the vessels. White arrow: blood vessel; blue arrow: trigeminal nerve; red arrow: trigeminal nerve and surrounding blood vessels. Scale bars: 1 cm. Please click here to view a larger version of this figure.

Figure 2: Preoperative three-dimensional reconstruction of skull CT imaging. (A) Medial view of the CT-reconstructed skull image demonstrating the sigmoid sinus groove and transverse sinus groove. (B) Three-dimensional CT reconstruction of the lateral skull base and craniocervical junction). Red arrows: sigmoid sinus groove and transverse sinus groove; blue arrows: parietal, occipital, and temporal bones and their intersection point, the 'star point'. Scale bars: 1 cm. Please click here to view a larger version of this figure.

Figure 3: Three-dimensional reconstruction of the patient's cranial CTA examination data. (A) A scaled three-dimensional reconstruction model of the patient's craniofacial skin tissue, preserving the original anatomical morphological features. (B) A vascular reconstruction model of the sigmoid sinus and transverse sinus, with the sinus confluence region clearly displayed in three-dimensional spatial configuration after digital trimming. (C) A sagittal section view of the cranial bone three-dimensional model, clearly showing the bony landmarks of the sulcus for the sigmoid sinus and the sulcus for the transverse sinus on the inner table of the skull. (D) The reconstructed image clearly demonstrates the three-dimensional topological relationships and spatial localization of the sigmoid-transverse sinus junction. Blue arrow: Reconstruction of the cranial skin; red arrow: Spatial relationship between the sinus and the sinus groove. Please click here to view a larger version of this figure.

Figure 4: Nail path planning function positioning 'strategic burr hole' and surgical path planning. (A) Axial positioning of the vascular sinus margin and surgical path optimization. (B) Coronary positioning of the vascular sinus margin and surgical path adjustment. (C) Sagittal positioning of the vascular sinus margin and surgical path optimization. (D) A three-dimensional image showing the nail path located at the angle between the sigmoid sinus and transverse sinus. The point where the nail path penetrates the skull is the 'strategic burr hole', and the direction of the nail path determines the direction of the 'strategic burr hole'. Red arrow: location of the nail and its relationship to the sigmoid sinus and transverse sinus. Please click here to view a larger version of this figure.

Figure 5: Guide plate design function generates a specific surgical guide plate: (A) Selecting the path extraction base surface option, and combining anatomical landmarks (zygomatic arch, nasal root, and 'strategic burr hole') to complete the three-dimensional selection of the surgical guide base plane. (B,C) After selecting the target area, executing the base surface generation master command to generate a master model that completely fits the patient's craniofacial structure. (D) Clicking on 'Generate Guide Plate,' the E-3D software automatically performs a Boolean operation between the master model and the drill path trajectory to generate a surgical guide plate with navigation functionality. Black arrow: path extraction base surface, red arrow: master model. Blue arrow: drill path trajectory. Please click here to view a larger version of this figure.

Figure 6: Three-dimensional visualization and verification of the surgical guide and screw trajectory. (A,B) Three-dimensional reconstruction analysis using E-3D software shows that the screw trajectory of the surgical guide design accurately penetrates the skull (i.e., the 'strategic burr hole'), with the positioning point accurately located at the anatomical intersection of the sigmoid sinus and transverse sinus. (C,D) Three-dimensional reconstruction of the guide model and registration verification of the physical 3D-printed guide show that the guide exhibits high morphological matching with the patient's craniofacial anatomical structures. Please click here to view a larger version of this figure.

Figure 7: 3D printed surgical guides to guide surgical procedures. (A) Following patient positioning, the patient-specific surgical guide is precisely placed in the designated operative area, ensuring accurate alignment with anatomical landmarks and the planned surgical trajectory. (B) Using a 5 mL syringe, puncture along the preset path of the surgical guide to the outer surface of the skull, and inject 0.05 mL of 1% methylene blue solution. (C) After incising the skin and subcutaneous tissue, the methylene blue markings on the skull surface are exposed, corresponding to the pre-planned 'strategic burr hole'. (D) Drilling holes according to the methyl blue marking points; the bone holes clearly show the margins of the vascular sinuses. Blue arrow: methylene blue marking point, white arrow: 'strategic burr hole', and the edge of the vascular sinus. Please click here to view a larger version of this figure.

Figure 8: CT image of the operated area. (A) Preoperative CT image. (B) CT imaging was conducted postoperatively for surgical assessment. Red arrow: Postoperative follow-up CT image of the surgical area. Please click here to view a larger version of this figure.

Table 1: Patient's preoperative MRI findings and postoperative improvement. Please click here to download this Table.

Table 2: Preoperative and postoperative pain, quality of life scores, craniotomy duration, and complications in patients. Please click here to download this Table.

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 facial spasms¹⁴. The positioning of the strategic burr hole varies depending on the lesion. For instance, retrosigmoid craniotomy for facial dystonia requires sufficient exposure of the operative area below the mastoid notch, with the posterior border of the sigmoid sinus serving as the base. In such cases, the strategic burr hole is positioned just below the junction of the sigmoid and transverse sinuses¹⁵. Accurate placement of the strategic burr hole minimizes excessive bone removal from the posterior fossa, reduces operative time, and decreases postoperative complications. Historically, intraoperative techniques such as skull bone marking, stereotactic methods, and neuronavigation have been limited in their ability to precisely localize the strategic burr hole or have faced challenges in practical application and widespread adoption¹⁶.

Since the 1990s, 3D printing technology has seen growing applications in fields such as aerospace, medicine, and architecture¹⁷. In medicine, its ability to produce personalized and precise products has significantly enhanced its clinical value. The affordability of 3D printers and materials, coupled with the ease of mastering the technology, has facilitated their adoption in developing countries¹⁸. Consequently, many developing nations are now utilizing 3D models for surgical simulation and training, achieving favorable outcomes¹⁹. Furthermore, advancements in 3D printing technology have led to the increasing use of 3D-printed models for surgical navigation and treatment planning²⁰. In this context, we employ patient-specific imaging data to accurately locate the strategic burr hole and create a 3D-printed model. This model not only provides visual guidance but also translates virtual 3D images from imaging workstations into tangible, three-dimensional tools for clinical use. Additionally, for other lesions requiring retrosigmoid craniotomy, 3D modeling software can integrate various imaging modalities, such as cranial CT, MRI, and CTA, to generate a fused 3D model. This model clearly delineates the anatomical relationships between the lesion and surrounding structures, enabling the formulation of a precise surgical plan.

The traditional 'star point' marking method has obvious anatomical limitations when locating 'strategic burr hole', primarily manifested in the inability to accurately display the edges of the venous sinuses, leading to the need for additional bone removal toward the venous sinuses using bone forceps during surgery. This approach not only causes postoperative cranial bone defects but also significantly prolongs craniotomy time, thereby increasing the incidence of postoperative CSF leakage²¹. In this study, pre-printed surgical guides accurately located the 'strategic burr hole' and clearly defined the edges of the venous sinuses. The removal of the bone flap in the surgical area was smooth, craniotomy time was significantly shortened, and bone defects during surgery were minimal (Table 2). The 3D-printed guide demonstrated good clinical outcomes, including no venous sinus rupture during surgery and no postoperative complications such as subcutaneous fluid accumulation, CSF leakage, or poor wound healing. Given the limited sample size of this study, large-scale clinical trials are needed to assess the safety, indications, and contraindications of 3D-printed guides in sigmoid sinus craniotomy. Additionally, standardized assessment criteria, such as guide positioning accuracy and size of the bony defect, should be established to evaluate the effectiveness of this technology.

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