Microvascular decompression through an anterior transpetrosal approach for trigeminal neuralgia caused by persistent primitive trigeminal artery variant traversing Meckel’s cave: A case report

Abstract

Background:

Trigeminal neuralgia (TN) is most commonly caused by neurovascular compression, and microvascular decompression (MVD) remains the standard surgical treatment for patients refractory to medical therapy. Rarely, TN is associated with persistent primitive trigeminal artery (PPTA) or its PPTA variant (PPTAv). TN caused by PPTAv traversing Meckel’s cave is extremely rare.

Case Description:

A 68-year-old female presented with TN affecting the left V2 and V3 distributions. Despite pharmacological management, her pain progressively worsened; therefore, MVD was performed. Preoperative magnetic resonance angiography and fast imaging employing steady-state acquisition revealed a PPTAv arising from the left internal carotid artery, coursing tortuously through Meckel’s cave before entering the posterior fossa. Neurovascular compression of the trigeminal nerve (cranial nerve V [CN V]) within Meckel’s cave by this vessel was identified as the cause of TN. To achieve adequate opening of Meckel’s cave, the anterior transpetrosal approach (ATPA) was selected. Intraoperatively, a markedly tortuous PPTAv was identified within Meckel’s cave. Opening Meckel’s cave enabled successful transposition of the PPTAv and decompression of CN V. Postoperatively, the neuralgia resolved completely, with no complications such as hearing impairment or cerebrospinal fluid leakage. At 6 months after surgery, the patient remained pain-free without recurrence and required no medication or additional treatment.

Conclusion:

We report a rare case of TN caused by a PPTAv passing through Meckel’s cave. Careful evaluation of preoperative imaging is critical in TN cases with atypical vascular anatomy. In this case, ATPA facilitated the safe opening of Meckel’s cave and the effective transposition of the offending vessel, suggesting that it may be a useful surgical option in carefully selected cases.

INTRODUCTION

Trigeminal neuralgia (TN) is a representative cranial nerve compression syndrome most commonly caused by neurovascular compression. Microvascular decompression (MVD) is considered the gold standard treatment for patients refractory to medical therapy.[1] In most cases, the offending vessels are the superior cerebellar artery (SCA) or the anterior inferior cerebellar artery (AICA).[12] However, in rare cases, TN may result from a persistent primitive trigeminal artery (PPTA) or its variant (persistent PPTA variant [PPTAv]), which represents a remnant of embryonic vascular development.[5]

Here, we report a rare case of TN caused by a markedly tortuous PPTAv coursing within Meckel’s cave. Based on preoperative imaging findings, the anterior transpetrosal approach (ATPA) was selected, allowing safe opening of Meckel’s cave and adequate transposition of the offending vessel, resulting in a favorable surgical outcome. This report describes the clinical and radiological features of this case. It discusses the anatomical characteristics of PPTA/PPTAv, their association with TN, the effectiveness of ATPA, and the importance of selecting an appropriate surgical approach. An edited high-definition video with detailed subtitles is included to illustrate this technique and its nuances [Video 1, Supplemental Digital Content].

CASE DESCRIPTION

Patient history and clinical presentation

A 68-year-old female with a history of hypertension, diabetes mellitus, and nephrotic syndrome presented with a 5-year history of paroxysmal pain in the left maxillary (V2) and mandibular (V3) distributions of the trigeminal nerve. Her pain was classified as Grade IV on the Barrow Neurological Institute (BNI) Pain Intensity Scale. She had been diagnosed with left TN at a previous hospital and was treated with carbamazepine at a dose of 800 mg/day. However, her pain persisted despite medical therapy, and she developed significant dizziness as a medication-related adverse effect. Because she declined nerve block therapy and preferred definitive surgical treatment, MVD was planned.

Preoperative imaging findings

Preoperative magnetic resonance angiography (MRA) revealed an artery arising from the dorsal aspect of the C4 segment (cavernous portion) of the left internal carotid artery. The vessel coursed markedly tortuously through Meckel’s cave and entered the posterior fossa [Figure 1A]. It ran along the trigeminal nerve (cranial nerve V [CN V]) and did not join the basilar artery; instead, it extended toward the lateral cerebellar hemisphere. Based on these findings, the vessel was diagnosed as a PPTAv (Saltzman type III).

Figure 1:

Preoperative magnetic resonance imaging findings. (A) Preoperative magnetic resonance angiography revealed a persistent primitive trigeminal artery variant (primitive trigeminal artery variant [PPTAv]; red arrowhead) arising from the dorsal aspect of the cavernous portion of the left internal carotid artery, which exhibited marked tortuosity within Meckel’s cave. The artery did not anastomose with the basilar artery and coursed laterally toward the cerebellar hemisphere. (B) Fast imaging employing steady-state acquisition imaging demonstrated compression of the trigeminal nerve (cranial nerve V; white arrowhead) by the tortuous part of PPTAv within Meckel’s cave.

High-resolution T2-weighted imaging (fast imaging employing steady-state acquisition [FIESTA]) suggested compression of CN V by this vessel within Meckel’s cave [Figure 1B]. Cerebral angiography confirmed the same vascular course observed on MRA and demonstrated that the distal branches perfused the ipsilateral AICA and posterior inferior cerebellar artery territories [Figure 2].

Figure 2:

Preoperative three-dimensional cerebral angiography findings. Three-dimensional cerebral angiography revealed a primitive trigeminal artery variant (PPTAv) (red arrowhead) with a course consistent with that observed on magnetic resonance angiography. PPTAv supplied the anterior inferior cerebellar artery and posterior inferior cerebellar artery.

A small lesion suggestive of a lipoma was also identified near the medial side of the root entry zone (REZ) of CN V; however, no compression of CN V was observed, and it was not considered the cause of TN.

Surgical procedure and intraoperative findings

Because preoperative imaging indicated severe tortuosity of the PPTAv within Meckel’s cave compressing CN V, the ATPA was selected to allow opening of Meckel’s cave and ensure adequate decompression.

Under general anesthesia, auditory brainstem response and facial nerve stimulation monitoring were established. A left temporal craniotomy was performed, and the middle cranial fossa base was flattened. The dura was dissected toward the foramen spinosum, and the middle meningeal artery was coagulated and divided. Slightly anteriorly, the foramen ovale, through which V3 exits the skull, was identified. The groove of the greater superficial petrosal nerve (GSPN) was confirmed using facial nerve stimulation. Interdural dissection was performed while preserving the GSPN and extended to the foramen ovale [Figure 3A].

Figure 3:

Intraoperative photographs. (A) Extradural dissection exposing the Kawase rhomboid. greater superficial petrosal nerve; cranial nerve V3, mandibular nerve. (B) Exposure of the posterior fossa dura mater following petrosectomy. (C) Transection of the superior petrosal sinus. (D) The primitive trigeminal artery variant (PPTAv) is gently drawn out after opening Meckel’s cave. CN: Cranial nerve, GSPN: Greater superficial petrosal nerve.

The Kawase rhomboid, located anterior to the internal auditory canal, was drilled (anterior petrosectomy), exposing the posterior fossa dura [Figure 3B]. The dura of the middle and posterior fossae was incised with the superior petrosal sinus (SPS) between them, and the SPS was transected anterior to the confluence with the petrosal vein [Figure 3C]. The superior wall of Meckel’s cave (the tentorium) was then incised and opened.

After dissecting the arachnoid surrounding CN V, the PPTAv was identified coursing from Meckel’s cave into the posterior fossa along the inferior aspect of CN V [Figure 3D]. As anticipated from preoperative imaging, the vessel exhibited marked tortuosity. The tortuous segment within Meckel’s cave was carefully mobilized into the posterior fossa, and both the proximal and distal segments were secured to the medial and lateral surfaces of the pons using Teflon slings to avoid contact with CN V [Figure 4A-C].

Figure 4:

Illustrations showing the primitive trigeminal artery variant (PPTAv) transposition process. (A) A highly tortuous PPTAv (transparent portion) coursing through Meckel’s cave. (B) Meckel’s cave was opened, and the tortuous segment was gently pulled outward to relieve the compression of cranial nerve V (CN V). (C) The PPTAv was fixed to the pons using Teflon slings at two points, medial and lateral to CN V.

A lipoma was observed near the REZ of CN V; however, no compression of the nerve was observed. The dura was closed using fascia lata, and the petrous bone defect was filled with abdominal fat and fibrin glue.

Postoperative course and imaging findings

The patient’s facial pain resolved completely after surgery (BNI Pain Intensity Scale: I). No postoperative complications, including hearing disturbance or cerebrospinal fluid leakage, were observed. Postoperative magnetic resonance imaging showed no brain contusion along the surgical corridor or venous infarction. Postoperative MRA confirmed successful transposition of the PPTAv, with resolution of its tortuous course within Meckel’s cave. FIESTA imaging verified that no structure was compressing CN V [Figure 5]. The patient was discharged without neurological deficits (modified Rankin Scale score: 0). At 6 months after surgery, the patient remained pain-free without recurrence and required no further treatment.

Figure 5:

Postoperative magnetic resonance imaging findings. (A) Postoperative magnetic resonance angiography confirmed the resolution of the tortuous course of the primitive trigeminal artery variant (red arrowhead) within Meckel’s cave. (B) Fast imaging employing steady-state acquisition imaging revealed no compressive structure on cranial nerve V (white arrowhead).

DISCUSSION

Embryology and prevalence of PPTA/PPTAv

PPTA is a fetal anastomotic vessel connecting the carotid and vertebrobasilar systems during early embryonic development.[6] The reported prevalence of PPTA detected by cerebral angiography or MRA ranges from 0.1% to 0.76%, making it the most common persistent fetal carotid–basilar anastomosis.[3] In 1959, Saltzman proposed a classification of PPTA based on its connection with the basilar artery.[7] Subsequently, Teal et al.[14] described a variant that continues directly to the SCA, thereby first describing the anatomical subtype later termed PPTAv. In 2012, Uchino et al.[15] provided a systematic description clearly distinguishing PPTA from PPTAv. The reported prevalence of PPTAv ranges from 0.18% to 0.76%.[3] However, cases in which PPTAv courses through Meckel’s cave and lies adjacent to CN V are extremely rare.

Pathophysiology of PPTA/PPTAv-related TN

TN is most commonly caused by compression from the SCA[1,12], whereas PPTA- or PPTAv-related TN is extremely rare.[13] Morita et al.[5] reviewed 1257 patients with TN who underwent MVD in 1989. Among these cases, only eight were attributed to PPTA/PPTAv. Notably, only one case involved a typical PPTA, whereas seven were associated with PPTAv. The authors suggested that PPTAv follows a more dorsal course than typical PPTA, bringing it into closer proximity to CN V and its REZ. Consequently, PPTAv may have a higher potential to cause TN.

Surgical technique and approach

The retrosigmoid approach remains the standard technique for MVD; however, visualization of anterior-posterior fossa structures, including Meckel’s cave, is often limited. Moreover, the posterolateral surgical trajectory may create a long and narrow operative corridor, increasing the risk of injury to the facial nerve (CN VII) and vestibulocochlear nerve (CN VIII), as well as interference from the petrosal vein.[11] Samii et al.[8] described a variation incorporating suprameatal drilling; however, limitations in accessing anterior-posterior fossa structures such as Meckel’s cave persist.

In contrast, ATPA provides a subtemporal corridor with removal of the petrous apex, allowing shorter and more direct access to the ventral brainstem and petroclival region. This approach enables visualization of CN V from its REZ to Meckel’s cave within a single operative field. Furthermore, it is less influenced by the petrosal vein and avoids manipulation of CN VII and CN VIII, potentially reducing the risk of cranial nerve injury.[10,11]

Reports of MVD for TN caused by PPTAv passing through Meckel’s cave are extremely limited. To date, following the report by Morita et al. describing five cases, only two additional individual case reports have been published.[4,5,18] In all previously reported cases, the neurovascular conflict was located within the cerebellopontine cistern, and decompression was achieved at that site using a retrosigmoid or similar posterior fossa approach [Table 1]. However, in the present case, neurovascular conflict was located predominantly within Meckel’s cave, where a markedly tortuous PPTAv compressed CN V. Adequate decompression required opening Meckel’s cave and mobilization of the tortuous vessel at the site of compression. Although a retrosigmoid approach with suprameatal drilling or endoscopic assistance might also have been feasible, we considered ATPA more suitable as it provides a wider and more direct exposure of Meckel’s cave, facilitating visualization of the entire neurovascular conflict and secure transposition of the offending vessel.

Table 1:

Summary of previously reported cases and the present case in which microvascular decompression is performed for trigeminal neuralgia caused by persistent primitive trigeminal artery variants passing through Meckel’s cave.

Another important consideration is the possibility of small branches arising from PPTA/PPTAv. Anatomical studies have demonstrated that PPTA may give rise to perforating branches to the brainstem as well as small branches around the trigeminal nerve.[17] Although angiography revealed no obvious branches within Meckel’s cave in our patient, the presence of very small branches could not be completely excluded. Therefore, wide exposure and meticulous microscopic inspection were considered advantageous for safe mobilization and transposition of the vessel.

We acknowledge that ATPA is more invasive than the conventional retrosigmoid approach and carries approach-specific risks, including cerebrospinal fluid (CSF) leakage and hearing-related complications, due to the opening of air cells in the petrous and temporal bones while drilling the petrous apex.[2,16] Therefore, this approach should be reserved for carefully selected cases in which its anatomical advantages are considered beneficial. In this patient, the risk was further increased due to long-term corticosteroid therapy for nephrotic syndrome and the need for postoperative steroid administration. At our institution, dural defects are reconstructed by suturing a fascia lata graft to the posterior fossa dura using 6-0 Prolene under microscopic visualization, and opened mastoid air cells are packed with abdominal fat. These techniques were applied in the present case, resulting in no postoperative CSF leakage or secondary complications, such as severe otitis media, even without lumbar drainage.

Careful selection of the surgical approach based on detailed preoperative imaging is also essential. Segawa et al.[9] reported two cases of TN caused by a markedly tortuous vertebrobasilar artery treated with MVD through ATPA. They demonstrated that this approach is effective when safe and adequate decompression is difficult using the conventional retrosigmoid approach. Although the retrosigmoid approach remains the standard, meticulous preoperative planning and appropriate selection of the surgical approach are critical in cases with atypical offending vessels or unusual vascular anatomy. Furthermore, the choice of surgical approach should be individualized according to the anatomical characteristics of the lesion and the surgeon’s experience and familiarity with the relevant skull base anatomy.

This report describes a single case; therefore, the effectiveness of ATPA cannot be generalized. TN caused by PPTA/PPTAv is rare, and further case accumulation and investigation are required.

CONCLUSION

TN caused by a markedly tortuous PPTAv within Meckel’s cave is extremely rare. In this case, successful treatment was achieved using the ATPA. The choice of surgical approach should be individualized according to preoperative imaging findings, anatomical characteristics, and the surgeon’s experience and familiarity with the relevant skull base anatomy.

Ethical approval:

Institutional review board approval is not required. This study was conducted in accordance with the ethical standards of the institutional and national research committee and with the Helsinki Declaration of 1975, as revised in 2000.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript, and no images were manipulated using AI.

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