Trigeminal neuralgia secondary to osteoma and vascular compression: illustrative case

Abstract

BACKGROUND

Trigeminal neuralgia (TN) is a common neurosurgical issue that has a detrimental impact on patients’ quality of life. Osteoma at the petrous apex is a rare etiology of TN. Here, the authors present a case involving the co-occurrence of petrous osteoma and a vascular loop around the trigeminal nerve. Both exerted pressure or compression on the exit of the trigeminal nerve.

OBSERVATIONS

A 46-year-old male presented with a 3-year history of persistent severe pain in the right side of his face. Magnetic resonance tomographic angiography of the trigeminal nerve revealed an abnormal signal in the right prepontine cistern, along with a vascular loop accompanying the right trigeminal nerve. A computed tomography scan of the skull indicated a nodular calcified density. The combined anterior transpetrosal approach for petrous osteoma and microvascular decompression (MVD) for the offending vessel were successfully performed. The patient was discharged without any complications or facial pain.

LESSONS

Although extremely rare, TN simultaneously secondary to petrous osteoma and offending vessels should be considered in the diagnosis. In this case, the combined surgical removal of petrous osteoma and MVD for the offending vessels proved to be an effective treatment for TN secondary to osteoma and vascular compression.

Trigeminal neuralgia (TN) is an typical condition characterized by neuropathic facial pain. Its prevalence is between 4 to 13 cases per 100,000 persons, primarily affecting individuals above the age of 50 years.^1,2 Updated diagnostic categories have been proposed.^3,4 Classic TN requires confirmation of morphological changes in the trigeminal nerve root resulting from vascular compression. Secondary TN is due to an identifiable underlying neurological disease. The most common factors contributing to secondary TN are tumors (such as meningiomas, acoustic neuromas, and epidermoid cysts), and less frequently, occurrences of aneurysms and arteriovenous malformations.⁵ A new classification of facial pain has been proposed that may predict surgical success.⁶ Typically, diagnosing TN is straightforward, primarily relying on the patient’s medical history. However, patients experiencing atypical facial pain have a more insidious onset of pain. Additionally, osteoma is an even rarer cause of this condition, and secondary TN caused by concurrent compression by both an osteoma at the petrous apex and offending vessels is exceedingly uncommon. The standard treatment for classic TN is microvascular decompression (MVD) of the trigeminal nerve. Here, we report the clinical case of a patient who had intractable TN caused by an osteoma and vascular compression and was treated with MVD in addition to osteoma excision.

Illustrative Case

History and Examination

A 46-year-old male presented with severe pain on the right side of his face that felt like electric shocks and was especially triggered by chewing food, severely affecting his quality of life. His only notable medical history was hepatitis B, for which he was undergoing regular medical treatment. Initially, he was treated by the neurology department with carbamazepine (200 mg, 3 times/day). The medication provided some relief during the initial phase of treatment. However, in April, the patient reported worsening of the right facial pain, leading to a referral for neurosurgical evaluation.

Upon examination, the patient exhibited paroxysmal pain in the right V1–V2 facial regions, without any other neurological signs. Magnetic resonance tomographic angiography (MRTA) of the trigeminal nerve showed that the lesion was hypointense on both T1- and T2-weighted images in the right prepontine cistern along with a vascular loop accompanying the right trigeminal nerve (Fig. 1). The trigeminal nerve MRTA enhancement scan indicated no enhancement in the lesion in the right prepontine cistern. Additionally, a computed tomography (CT) scan of the head indicated a nodular calcified density in the right prepontine cistern (mean CT number of osteoma: 902.7 Hounsfield units [HU]), measuring approximately 17 mm × 11 mm × 12 mm (Fig. 2). Because the osteoma at the petrous apex cannot be resected en bloc through the retrosigmoid approach and the surgical risk is increased due to segmented resection of the osteoma, it was decided to proceed with a right anterior transpetrosal approach to excise the osteoma tissue at the apex of the petrous bone and to explore the right trigeminal nerve, and then to determine the necessity of MVD.

FIG. 1.

Preoperative axial magnetic resonance imaging (MRI). A and B: Magnetic resonance tomographic angiography (MRTA) sequences showed the lesion was hypointense on both T1- and T2-weighted images (yellow arrows). C: MRTA sequences showed the trigeminal nerve was closely related to the lesion (green arrow). D: The right trigeminal nerve was accompanied by offending vessels (red arrow).

FIG. 2.

Preoperative axial computed tomography (CT) showing a clustered calcified density shadow in the right prepontine cistern (mean CT number of osteoma: 902.7 Hounsfield units [HU]), causing compression changes near the brainstem.

Surgery

The surgical plan was to first remove the osteoma, followed by exploration and possible decompression of the trigeminal nerve. The patient underwent an anterior transpetrosal approach. Afterward, the patient was positioned in the left lateral decubitus with the head in a park-bench position, and a straight incision was made in front of the right ear. Once the skull was exposed, a burr hole was made at the middle skull base, and the dura mater was suspended and incised. The craniotomy was planned to gain access flush with the base of the middle fossa. The temporal base was lifted, and the petrous bone was located, with the dura mater being incised above it. The petrous ridge was obstructing the view, so it was partially removed with a drill, revealing a tumor located below the petrous ridge, with a hard bony texture (Fig. 3). Because of the osteoma occupying the space, only the compressed and displaced trigeminal nerve was visible initially. Under the microscope, given the inability to resect the osteoma in pieces and the challenge of separating it from the overlying dura mater, the only viable approach was to remove the osteoma along with the dura mater. After complete removal of the osteoma, it was discovered that the trigeminal nerve root was compressing the superior cerebellar artery, and then a piece of Teflon (Balance Medical, China) was used to separate the offending vessel from the nerve root (Fig. 4). During the procedure, the trochlear nerve, trigeminal nerve, and abducent nerve were preserved intact. After confirming hemostasis, closure was performed in layers with the usual technique. There were no complications during the procedure.

FIG. 3.

Intraoperative images, first stage. Initial views (A–D) of the right prepontine cistern angle. Identification and complete resection of the osteoma (green arrows) around the trigeminal nerve.

FIG. 4.

Intraoperative images, second stage. A: Initial view after extracting the osteoma, from the lateral region of the trigeminal nerve (V) toward its exit point of the superior cerebellar artery (SCA) pons branch (green arrow). B: After microsurgical dissection, the SCA branch of the trigeminal nerve is separated. Placement of a piece of Teflon (T) between the vascular loop and the trigeminal nerve (green arrow). Final view of the trigeminal nerve free of any vascular compression.

The patient showed no additional neurological symptoms after extubation, and his facial pain disappeared. The patient was discharged 5 days after the surgery. The histopathological examination of the excised lesion confirmed the diagnosis of osteoma (Fig. 5). A follow-up CT scan on the third day after the surgery revealed no evidence of osteoma in the prepontine cistern. The patient reported the disappearance of facial pain 1 month after the surgery during a follow-up visit.

FIG. 5.

Fractured mature lamellar bone tissue consistent with osteoma was detected at the apex of the right petrous bone. Hematoxylin and eosin, original magnification ×100.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

Trigeminal neuralgia is a common and widely recognized neurosurgical condition that significantly impacts quality of life. Although TN is slightly more frequent on the right side, bilaterality can be seen in 5% of classic cases.^7,8 Trigeminal neuralgia is classified as classic, secondary, or idiopathic.^3,4 Undoubtedly, the primary cause of classic TN is often attributed to trigeminal neurovascular compression with morphological changes.

Among secondary TN cases, facial pain can be caused by lesions that occupy space in the prepontine cistern or cerebellopontine angle (CPA). Reported cases have included meningiomas, schwannomas, epidermoid cysts, arachnoid cysts, and arteriovenous malformations. In particular, osteoma of the petrous apex protruding into the CPA is rare, and it is even rarer for an osteoma to play a significant role in the pathogenesis of TN. In our case, TN simultaneously secondary to a petrous osteoma and the offending vessel has been reported, which improved after combined surgical removal of the petrous osteoma and MVD for the offending vessels.⁹

The mechanism by which osteoma at the apex of the petrous bone causes TN is unclear, but it is hypothesized that the neuralgia may be linked to the compression, irritation, or distortion of the trigeminal nerve caused by the expanding lesion.¹⁰ Specifically, demyelination along the trigeminal afferent pathway is a major driver for TN pathophysiology, where pathological demyelination can be triggered by physical compression of the trigeminal nerve. The petrous osteoma was believed to have chronically compressed the cisternal segment of the trigeminal nerve, leading to mechanical demyelination of the nerve and the subsequent development of secondary TN. So far, a few cases of secondary TN due to osteoma have been reported,^11,12 which suggests that TN secondary to petrous osteoma may not be as uncommon as previously thought. Abdulla et al.¹³ reported a case in which osteoma originated from the clivus and extended into the CPA. That patient had a history of facial pain, primarily attributed to the pushing and compression of the trigeminal nerve fibers within Meckel’s cave by the osteoma. Complete relief was achieved for secondary TN following surgical removal of the petrous osteoma.¹¹ As we reported in this case, the osteoma of the petrous apex protruded into the CPA, compressing the trigeminal nerve, which may also be one of the direct factors leading to TN. In the operation, the osteoma of the petrous apex was removed as a whole, and direct compression of the trigeminal nerve by the osteoma was relieved.

The mass effect of the osteoma could also be one of the causes leading to TN, in addition to the facial pain caused by direct compression of the trigeminal nerve by the osteoma. The mass effect induced by osteoma of the petrous apex could have led to a local reduction in space. This effect pushed and displaced the trigeminal nerve, forcing it in contact with the superior cerebellar artery. The offending vessel came into even greater proximity to the trigeminal nerve, resulting in greater pressure that further accentuated the nerve’s compression of the vessel and then caused neuralgia. Samii and Matthies¹⁴ proposed that, in cases of TN secondary to brain tumors, further investigation is necessary to identify potential offending vessels and to perform MVD after tumor removal. In our case, following excision of the osteoma, we adequately exposed the entire course of the trigeminal nerve, meticulously examined suspicious offending vessels, and performed a thorough decompression. Besides the factor of direct compression of the trigeminal nerve by the osteoma, we believed that the mass effect of the osteoma led to displacement of the trigeminal nerve. This phenomenon resulted in a closer relationship with the neighboring offending vessel, causing compression of the nerve against this adjacent vessel, and becoming a significant factor in the onset of TN. Therefore, in cases of secondary TN, our focus should not only be on osteoma compression but also the mechanism of trigeminal nerve compression against neighboring offending vessels.⁸

Consequently, we presumed that the patient’s facial pain was primarily a result of the combined compression caused by both the osteoma and the offending vessel. This included direct compression of the nerve by the osteoma, along with the mass effect of the osteoma, compelling the trigeminal nerve to shift in proximity to the offending vessels, resulting in compression of the offending vessels of the trigeminal nerve.

Lessons

Osteoma originating from the petrous apex is uniquely located and extremely rare. The conventional surgical approach preferred for classic TN increases the surgical complexity when dealing with an osteoma of the petrous apex. An osteoma at the petrous apex cannot be excised in pieces and must be removed as a whole, potentially raising the surgical risks associated with the retrosigmoid approach. Therefore, it is advisable to choose the anterior transpetrosal approach.¹⁵ While extremely rare, there can sometimes be more than one possible etiology of TN in the same patient. In these circumstances, it is difficult or impossible to know which abnormality is the source of the patient’s symptoms, and it may be wise to address both abnormalities in a single operation. Hence, the current case demonstrated that the combined surgical removal of the petrous osteoma and MVD for the offending vessel was an effective treatment for TN secondary to osteoma and vascular compression.

Author Contributions

Conception and design: Jiang, Li. Acquisition of data: Jiang, Li. Analysis and interpretation of data: Cao. Drafting of the article: Cao. Critically revising the article: Jiang, Cao, Wu. Reviewed submitted version of the manuscript: Jiang, Cao. Approved the final version of the manuscript on behalf of all authors: Jiang. Study supervision: Cao.