A unique presentation of trigeminal neuralgia related to a central nervous tissue choristoma along the trigeminal nerve root: illustrative case

Abstract

BACKGROUND

Trigeminal neuralgia (TNa), or tic douloureux, is characterized by severe facial pain triggered by everyday activities. Recurring and intense TNa pain results from localized demyelination within the affected nerve segment. The primary cause of TNa is typically vascular compression, with the superior cerebellar artery being the most common vessel. Tumors, multiple sclerosis, and infectious diseases such as herpes are less frequent causes of TNa.

OBSERVATIONS

The authors present a unique case in which TNa was caused by an aberrant mass resembling a schwannoma during surgery. However, histological examination revealed heterotopic benign central nervous neurons and myelinated axons, which could represent a choristoma in the cisternal segment of the portio major of the trigeminal nerve. Following surgery, the patient’s TNa was completely resolved.

LESSONS

To the best of the authors’ knowledge, this is the first documented case of a central nervous tissue choristoma causing TNa and responding positively to surgical intervention, aside from one previous report that did not specifically use the term “choristoma” in identifying the lesion. This case highlights the challenges involved in diagnosing and managing a rare TNa presentation, with a particular focus on pathology findings. It underscores the potential role of surgery for patients whose condition is resistant to medical intervention.

https://thejns.org/doi/10.3171/CASE24384

The trigeminal nerve (TN) is the largest cranial nerve (CN) and has a dual role in both sensory input of the face and motor control of the muscles of mastication.¹ The TN can be classified into six segments based on anatomical location. These include the pontine, cisternal, ganglionic, preforaminofissural, foraminofissural, and extracranial segments.² The TN emerges from the anterolateral pons with a larger sensory (portio major) and smaller motor (portio minor) component. It then travels through the prepontine and cerebellopontine angle (CPA) cisterns before entering the trigeminal recess, Meckel’s cave, via the dura mater’s porus trigeminus. Within the trigeminal recess, the ophthalmic, maxillary, and mandibular divisions of the nerve arise from the trigeminal ganglion.¹

Trigeminal neuralgia (TNa), or tic douloureux, is an intense, shock-like facial pain affecting the sensory distribution of the TN, often triggered by everyday activities.³ The most common reason for TNa is compression by nearby vessels. While compression by the superior cerebellar artery is the most common cause, compression by the anterior inferior cerebellar artery, vertebral artery, and even local veins could also lead to TNa.⁴ In rare instances, TNa might be linked to various uncommon factors, including tumors in the CPA, demyelinating disorders such as multiple sclerosis, infarction of the pons, infections such as herpes simplex, congenital or acquired bone irregularities such as petrous apex hyperplasia, encephalocele/meningocele, and systemic conditions such as Marfan syndrome.^{5, 6} Compression of the TN by a mass lesion, blood vessels, or other irritants causes localized demyelination in the affected nerve segment. This demyelination leads to spontaneous and abnormal nerve impulses, resulting in brief, sudden, and recurring pain known as TNa.⁷

We present a unique case of TNa caused by a nonneoplastic, heterotopic mass of central nervous tissue, known as “choristoma,” in the cisternal segment of the portio major of the TN, an unprecedented occurrence to the best of our knowledge. This case report aims to elucidate this rare presentation’s clinical course, diagnostic challenges, treatment, and outcomes, contributing to a better understanding of diverse TNa etiologies.

Illustrative Case

History and Examination

A 65-year-old male patient presented with a 2-year history of left-sided TNa that was unresponsive to gabapentin and carbamazepine. The pain typically originated from the left ear and radiated into the jaw. Notably, the pain was triggered by exposure to cold water, washing his face, and eating. The patient did not exhibit numbness at the presurgical site of pain.

Cranial magnetic resonance imaging (MRI) revealed a 3 × 2–mm structure along the lateral margin of the cisternal segment of the left TN. This mass exhibited a low signal on the high-resolution T2-weighted sequence. No enhancement was observed on postcontrast imaging, with a presumptive diagnosis of vascular compression versus a nonenhancing trigeminal schwannoma (Fig. 1). After discussing the pros and cons of continued observation versus surgical removal, the patient chose surgery and subsequently underwent a left retrosigmoid craniotomy to explore and possibly address microvascular compression or resection of the tumor.

FIG. 1.

Preoperative T2-weighted MRI (A–C) demonstrating the mass (arrows). Postoperative axial contrast T1-weighted (D) and T2-weighted (E and F) MRI showing gross-total resection of the lesion.

Microsurgical Approach

The patient was placed supine, and the sigmoid and transverse sinuses were marked using neuronavigation. A postauricular C-shaped skin incision was outlined. Following the skin incision, a myocutaneous flap was elevated and retracted. A single burr hole was placed just below the junction of the sigmoid and transverse sinuses, and then a retrosigmoid craniotomy was performed.

After the retrosigmoid craniotomy was performed, the cerebellum was gently retracted, and cerebrospinal fluid was drained for brain relaxation. The arachnoid mater was then opened posterior to the facial and the vestibulocochlear nerve complex, creating a wider corridor toward the TN at the petrotentorial junction. No neurovascular conflict was observed after extensive dissection around the TN. However, a small mass was identified on the portio major of the TN, approximately 1 cm from its point of attachment to the pons, suggesting the possibility of a TN schwannoma. After division of the rootlet with scissors, the mass was removed in one piece and was submitted for pathological evaluation (Fig. 2, Video 1).

FIG. 2.

A: Intraoperative photograph revealing a mass on the portio major of the TN and involved fibers. B: Intraoperative photograph revealing the portio major, portio minor, and cavity on the portio major after mass removal.

VIDEO 1. Clip showing an unprecedented ganglion cell aggregation in the TN masquerading as a schwannoma, which presented as a case of TNa. AICA = anterior inferior cerebellar artery. Click here to view.

The paraffin sections stained with hematoxylin and eosin (H&E) revealed a noncapsulated cylindrical lesion measuring 0.4 cm in length and just under 0.2 cm in diameter. The tissue consisted of about three poorly defined clusters of mature neurons, ranging between 20 and 40 µm in largest diameter (Fig. 3B and C). The nuclei of these neurons were eccentrically positioned, and the basophilic (Nissl) substance was evenly dispersed in the perikaryon. Satellite cells, binucleation, and dysplastic features were not observed in association with these neurons. A mild crush artifact was visible in some neurons, along with granulovacuolar bodies and one neurofibrillary tangle–like structure. The Luxol fast blue combined with periodic acid–Schiff stain confirmed that the background was composed of abundant teal-blue–staining myelinated axons, representing central-type myelin (Fig. 3A). A minute fascicle of fibers with dark blue–staining peripheral myelin was identified only at the distal end of the mass. Using a neurofilament antibody, axons were noted to be mostly arranged in parallel bundles, forming fascicles (Fig. 3D). The GFAP antibody confirmed the presence of a small number of randomly distributed reactive astrocytes, representing gliosis.

FIG. 3.

A: At low magnification, the bulk of the cylindrical mass contains myelinated axons surrounded with central-type myelin that stained teal blue. At the lower corner (arrow) and in the inset, a small amount of dark blue myelin representing peripheral myelin is evident. Luxol fast blue combined with periodic acid–Schiff stain, original magnification ×2 and ×40 (inset). B: Arrows point to ill-defined clusters of neurons. H&E stain, original magnification ×4. C: At higher magnification, the H&E stain reveals several neurons (arrows) within each cluster. Original magnification ×4. D: Axons organized in bundles (arrows) are highlighted with the neurofilament antibody. Original magnification ×4.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

The International Association for the Study of Pain categorizes TNa into three types: idiopathic TNa, having no apparent cause; classic TNa, resulting from compression of the TN by a nearby blood vessel; and secondary TNa, resulting from significant neurological conditions such as multiple sclerosis and CPA tumors.⁸ The primary cause of TNa is often vascular in nature, with the superior cerebellar artery being the most frequently implicated vessel. Among secondary causes, multiple sclerosis stands as the most common factor contributing to TNa, with a prevalence ranging from 1% to 6.3%. Intracranial tumors are the next most common cause. Meningiomas in the petrous apex and epidermoid tumors are the most commonly recorded tumors associated with TNa. Due to their proximity to the TN, even with a slight growth in size, these tumors might result in TNa.^{9, 10}

In the context of TNa, meningioma-induced cases tend to exhibit direct or indirect vascular involvement, while epidermoid tumors primarily cause a mass effect without necessarily involving the vessels. Moreover, local irritation triggered by chemical substances, such as cholesterol and keratin found in epidermoids, that seep through the cyst’s outer layer could initiate inflammation and could cause harmful effects on the TN root, leading to a breakdown of the myelin sheath.⁷

Compression of the TN by mass lesions, blood vessels, or occasionally chemical irritants results in localized demyelination along the affected nerve segment. This demyelination can lead to spontaneous activation and the generation of abnormal nerve impulses. These atypical nerve impulses give rise to recurring, shock-like, and momentary pain called “TNa.”⁷

This case report details the findings of a patient with TNa symptoms caused by a small structure involving the cisternal portion of the TN. The initial neuroimaging examination suggested that this was a vascular compression, which is commonly linked with TNa or nonenhancing trigeminal schwannoma. Stereotactic radiosurgery (SRS) was not considered as a potential alternative treatment for TNa related to mass lesions in this particular case, since we believed that the more likely cause was vascular compression. However, SRS can be an alternative treatment for small trigeminal tumors.¹¹ During surgery, it appeared to us that the mass might have been a schwannoma. However, microscopic examination revealed the mass to be a collection of benign and somewhat organized mature heterotopic neurons and central white matter, which we referred to as “choristoma.” We describe this as a choristoma, defined as a collection of histologically normal tissue elements located heterotopically in another tissue, as opposed to a hamartoma, which refers to a mass composed of disorganized mature/benign tissue elements belonging to the host tissue or organ.

This small mass was removed along the sensory nerve root/portio major of the TN. It was approached through an opening in the meningeal layer of the dura covering the TN root and ganglion. The mass was located approximately 1 cm from the TN root’s attachment to the pons. Intraoperatively, this mass measured nearly equal to the material seen in the paraffin sections, indicating that there was an opportunity to evaluate the entire lesion microscopically. During surgery, TN fibers were noted to enter and exit the mass (Fig. 3A, Video 1). Although we assume that the pain relief was due to the removal of the choristoma, we cannot rule out that pain relief might have been attributable to neurolysis by fascicle dissection or by a combination of neurolysis and mass removal.

Histological evaluation revealed a minute peripheral nerve segment entering one pole of the mass, presumably the caudal/distal end of the mass. In contrast, the rest of the mass consisted of relatively organized aggregates of neurons separated by well-formed bundles of axons with central myelin sheaths (Fig. 3). This is significant because, as in the TN, the transition from peripheral to central myelin takes place within a 0.2-cm distance from the pons, while this lesion was about 1.0 cm away from the pons. The mass is thus a heterotopic aggregate of central nervous tissue, with sensory-type neurons ranging between 20 and 40 µm, resting along the TN root. The lack of satellite cells suggests that these neurons are not misplaced trigeminal ganglion neurons.

Central nervous tissue choristomas are rare, with even fewer instances noted intracranially. By far, the majority of the cranial and intracranial choristomas that have been reported are composed of other tissue elements and do not represent central nervous tissue. These are mostly of mesenchymal origin, including an admixture of smooth muscle cells, skeletal muscle, peripheral nerve, glands, fibroadipose connective tissue, bone, or cartilage. Choristomas involving the CNs include glandular and smooth muscle involving the optic nerve;^12–14 smooth muscle and peripheral nerve elements involving the eighth CN/internal auditory canal;^15–17 and smooth muscle, striated muscle/rhabdomyoma, and central nervous tissue involving the TN.^18–20 In particular, the latter, described as a central nervous system (CNS) hamartoma, presented with TNa in the ophthalmic and maxillary distributions of the TN.²¹ Many other choristomas that have been reported involve fetuses, infants, and newborns and are likely better defined as glioneuronal heterotopias as part of CNS malformation.²²

Of interest, the neurons in our patient display similarities with the neurons of both the principal and the spinal trigeminal nucleus, suggesting the possibility that the mass in question contains second-order, somatic sensory neurons of the trigeminal pathway. While a definitive mechanism for the development of choristomas has not been identified to date, morphological similarities of neurons iin our patient to those of sensory trigeminal nuclei suggest the possibility that this particular choristoma could represent a focal migrational disorder related to TN development. This mass was not of TN origin because it did not consist of ganglion cells, and the proximal trunk did not reveal a transition from central to peripheral myelin. It solely consisted of central myelin. Since this was a cisternal CNS mass outside the confines of the pia that surrounds the intracranial CNS, we think that the most appropriate descriptive term is “choristoma,” as this has been used previously to identify this type of tissue occurrence.

Lessons

Our case underlines how clinical presentations can deviate from traditional diagnostic expectations, emphasizing the importance of considering atypical diagnoses in complex cases. Despite the unique nature of this choristoma-induced TNa, the fundamental role of surgical intervention in managing TNa remains unequivocal. The case further highlights that surgery is often the primary therapeutic recourse for patients with TNa that is unresponsive to medical treatment. Additionally, it demonstrates the necessity for thorough diagnostic evaluations and intraoperative exploration to identify rare causes like choristomas, reinforcing the value of tailored surgical approaches in effectively addressing diverse etiologies of TNa.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Baskaya, Ataoglu, Erginoglu, Sapanci, Salamat. Acquisition of data: Baskaya, Ataoglu, Erginoglu, Sapanci, Salamat. Analysis and interpretation of data: Erginoglu, Aydin, Sapanci, Salamat. Drafting the article: Erginoglu, Aydin, Sapanci, Salamat. Critically revising the article: Baskaya, Erginoglu, Salamat. Reviewed submitted version of manuscript: Baskaya, Ataoglu, Erginoglu, Salamat. Approved the final version of the manuscript on behalf of all authors: Baskaya. Administrative/technical/material support: Ataoglu, Salamat. Study supervision: Ataoglu.

Supplemental Information

Videos

  Video 1. https://vimeo.com/1002007447.

Correspondence

Mustafa K. Baskaya: School of Medicine and Public Health, University of Wisconsin–Madison, Madison, WI. baskaya@neurosurgery.wisc.edu.