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IMAGING EVALUATION OF TRIGEMINAL NEURALGIA/Trigeminal Nevraljide Goruntuleme.

Introduction

Classic trigeminal neuralgia (TN) is an episodic stabbing facial pain syndrome followed by a period of relief in the sensory distribution of the trigeminal nerve (cranial nerve V; CN V). The pain may be triggered by mild sensory stimulation such as light touch, washing, cleaning teeth and shaving; and it can disrupt daily living and lead to depression (1). The anatomy of CN V will be briefly reviewed followed by a discussion on commonly implicated conditions in TN (Table 1).

Anatomy of the fifth cranial nerve

CN V is the largest cranial nerve and it has a mixed sensory and motor function (2). In the brainstem, there are three sensory and one motor trigeminal nuclei (2, 3). The mesencephalic nucleus mediates facial proprioception. In the pons, approximately at the level of the cisternal segment of CN V, the primary sensory nucleus mediates facial tactile sensation, and the motor nucleus innervates the muscles of the first branchial arch (Figure 1) (2). The spinal nucleus of CN V mediates facial pain and temperature, and is the largest nucleus extending from the dorsal aspect of the pons into the upper cervical cord. The cisternal segment of CN V arises from the anterolateral aspect of the pons (Figure 1), and consists of a large sensory root comprising the main bulk of the nerve, and of one or more smaller motor roots arising superomedial to the sensory root (4). The cisternal segment of CN V crosses the cisternal space and enters the Meckel's cave through the porus trigeminus (Figure 1). The trigeminal (or semilunar or gasserian) ganglion is centered along the anterior, inferior and lateral wall of the Meckel's cave, which is essentially a cerebrospinal fluid (CSF) filled space continuous with the subarachnoid space of the basal cisterns through the porus trigeminus (5). The ophthalmic (V1) and the maxillary division (V2) of CN V enter the cavernous sinus anterior to the Meckel's cave, whereas the mandibular divisions (V3) of CN V extends inferolateral to exit the skull base through the foramen ovale without entering the cavernous sinus (2). V1 courses along the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure. V2 is also situated along the lateral wall of the cavernous sinus inferior to V1, and exits the skull base through the foramen rotundum to enter the pterygopalatine fossa. V3 never enters the cavernous sinus, but instead courses through foramen ovale to extend into the masticator space. V1, V2, and V3 supply sensory innervation to the upper, mid, and lower third of the face, respectively (2). CN V provides motor innervation to the muscles of mastication (medial and lateral pterygoid, masseter, and temporalis muscles), the mylohyoid, the anterior belly of the digastric, the tensor veli palatini, and the tensor tympani muscles.

Neurovascular conflict

Classic TN is most commonly secondary to neurovascular conflict (80-90%), which refers to symptomatic compression of the cisternal segment of CN V by an artery or less commonly a vein (6). Neurovascular conflict can range from simple contact to severe compression, displacement and nerve volume loss (Figure 2) (7). The most common offending vessel is the superior cerebellar artery followed by the anterior and inferior cerebellar artery (6). Neurovascular contact is common in asymptomatic patients and in the asymptomatic side; and neurovascular contact alone cannot be used for diagnosis of TN without the appropriate clinical context (8). Symptomatic neurovascular conflict tends to involve the proximal half of the cisternal segment of CN V (9), and to produce nerve root displacement and atrophy (6). However, in a large series of patients that underwent microvascular decompression, neurovascular conflict was observed throughtout the cisternal segment of CN V (10). Furthermore, in a small series of TN due to venous compression, the offending vein was more common in the midcisternal segment and the porus trigeminus (11).

In our practice, when a patient presents for MRI with documented TN by clinical history and evaluation, any neurovascular contact or compression, arterial or venous, proximal or distal, is included in the final radiologic report along with morphologic alterations of the nerve (i.e., deformity, atrophy). The cisternal segment of CN V is evaluated best with high-resolution three dimensional heavily T2-weighted sequences, such as constructive interference in steady state (CISS), and fast imaging employing steady-state acquisition (FIESTA) (7, 12). Less common causes of TN caused by vascular compression of the cisternal segment of CN V include saccular aneurysm, arteriovenous malformation, vertebrobasilar dolichoectasia, dural arteriovenous fistula, and persistent trigeminal artery (1-3).

Other causes of TN

Evaluation of patients with TN with MRI for the presence of neurovascular conflict allows simultaneous evaluation for other causes (6, 7). A number of lesions occurring anywhere from the trigeminal nuclei to the most distal branches can cause facial pain (9), and relevant differential considerations are going to be reviewed starting proximally at the level of the brainstem.

Brainstem

Multiple sclerosis (MS) is the most common cause of trigeminal neuropathy in the brainstem (Figure 3A) (3). MS patients have a 20-fold increased risk for TN compared to the general population (13). Demyelinating plaques may involve the trigeminal nuclei, the fascicular fibers in the brainstem, or extend into the root entry zone of the cisternal segment (7). However, it should be kept in mind that neurovascular conflict may be the cause of pain in MS, and selected MS patients may benefit from microvascular decompression to separate the offending vessel from the cisternal segment of CN V (14). Various mass lesions in the brainstem, such as primary and metastatic tumors, and cavernous malformations (Figure 3B), may involve the nuclei and/or the fascicular fibers of CN V (2, 15). A cavernous malformation may cause isolated TN, whereas neoplasms tend to produce more complex neurologic syndromes including long fiber tract and additional cranial nerve involvement (Figure 3C) (2). Cavernous malformations have a typical imaging appearance on MR due to blood degradation products that usually allows for a confident diagnosis (12). Infection involving the brainstem is called rhombencephalitis, and it may affect the trigeminal nuclei. Common pathogens include viruses, fungi, and Listeria (2, 12). In herpetic neuralgia, there is centripetal transaxonal spread of the virus along CN V fibers to the brainstem nuclei (16). Hyperintense T2 signal may be observed involving the spinal trigeminal nucleus in trigeminal zoster (Figure 3D), Ramsay-Hunt syndrome, and in trigeminal neuropathy associated with herpes labialis (17). Transient enhancement of the cisternal segment of CN V has also been described in infectious neuritis (12). Posterior inferior cerebellar artery infarcts may involve the spinal trigeminal nucleus. The most common presentation is lateral medullary/Wallenberg syndrome, which includes ipsilateral facial pain and temperature loss (3). Isolated trigeminal neuropathy due to infarct is uncommon (2).

Cisternal space and Meckel's cave

The cisternal segment of CN V may be involved, compressed and distorted by a wide variety of neoplasms and lesions (3, 12), which may present with TN accompanied by sensory loss (7). Trigeminal schwannomas are the most common primary neoplasm of CN V and the second most common intracranial schwannoma following vestibular lesions (Figure 4A) (18). They may arise anywhere distal to the transitional zone in the cisternal segment, where the centrally myelinated portion of the nerve (oligodendrocytes) transitions to the peripherally myelinated portion of the nerve (Schwann cells) (9). Central myelination and thus the transitional zone may be located up to approximately the mid aspect of the cisternal segment of CN V (9). Schwannomas are benign nerve sheath tumors that may occur sporadically or in the setting of Neurofibromatosis type 2 (18). Most trigeminal schwannomas occur in the Meckel's cave (18), and tend to grow in the parasellar region or extend through the porus trigeminus in the posterior fossa along the cisternal segment of the nerve (15). Vestibular schwannomas may enlarge enough to cause TN (1, 12). Other common benign lesions in the skull base that may present with TN or trigeminal dysfunction include meningioma (Figure 4B) and epidermoid (Figure 4C). They may affect CN V in the cisternal space or the Meckel's cave (2, 15, 19). TN, typical or atypical, was the presenting symptom in 10 out of 16 patients with Meckel's cave meningioma, and larger lesions tend to have additional cranial nerve deficits (20). CN V in the cisternal space is susceptible to a number of a leptomeningeal processes, including carcinomatosis, lymphoma, leukemia, sarcoidosis, and meningitis (3, 12). Benign or malignant involvement of the cisternal segment of CN V presents with enhancement on imaging (Figure 4D), and the nerve itself may be enlarged (12). Skull base lesions, such as chordoma, chondrosarcoma, multiple myeloma and bony metastases, may grow exophytically in the basal cisterns to impinge on the nerve or may invade the Meckel's cave directly (2). Tumoral involvement of the Meckel's cave is well demonstrated on T2-weighted images due to effacement of the normal fluid intensity signal due to CSF (15), and mass-like enhancement confirms neoplastic tissue. Skull base osteomyelitis in the petrous apex may extend into the adjacent Meckel's cave to produce TN (Figure 5A). The classic Gradenigo syndrome triad is completed with the addition of diplopia due to involvement of the abducens nerve in the Dorello canal in the petroclival region and deafness due to concurrent suppurative otitis media (2, 21).

Cavernous sinus

Trigeminal schwannomas in the cavernous sinus usually arise in the Meckel's cave and demonstrate secondary anterior extension (2). Additional neoplastic considerations in the cavernous sinus leading to trigeminal neuropathy include meningioma, pituitary macroadenoma (Figure 5B), lymphoma, nasopharyngeal carcinoma (Figure 5C) and metastatic disease (2, 12, 21). Tolosa-Hunt syndrome (THS) is an idiopathic inflammatory syndrome specific to the cavernous sinus and the orbital apex leading to painful ophthalmoplegia (21); and trigeminal branches may be involved. Typical imaging findings in THS include T2 hypointense signal and homogeneous intense enhancement. Vascular lesions that may involve the cranial nerves III, IV, VI, V1 and V2 in the cavernous sinus include cavernous carotid aneurysm and carotid cavernous fistula (2, 12). Trigeminal symptoms are present in approximately one third of these patients (3). Infection may spread from the paranasal sinuses intracranially into the cavernous sinus, and the typical scenario involves an immunosuppressed host including diabetic patients (12).

Extracranial space

The most common extracranial cause of trigeminal neuropathy is perineural spread of head and neck malignancies (2, 15). Commonly implicated lesions in perineural spread include squamous cell carcinoma, adenoid cystic carcinoma, lymphoma, melanoma, and sarcoma (22). The abnormal enhancement may track along the extracranial trigeminal divisions intracranially to involve the cavernous sinus (Figure 5D), the Meckel's cave, the cisternal segment of CN V, and rarely the brainstem (7). Nerve sheath tumors may arise from the extracranial branches of CN V, but are uncommon comprising only 5% of trigeminal schwannomas (2).

Conclusion 11.

TN is a clinical diagnosis, and the most common cause is neurovascular conflict affecting the cisternal segment of CN V. MRI is helpful to confirm neurovascular contact when present and to exclude other causes, which may occur anywhere from the brainstem to the extracranial space.

Source of funding

None declared.

Conflict of interest

None declared.

References

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Corresponding Author:

Marinos KONTZIALIS

Department of Radiology

Rush University Medical Center

1653 W Congress Pkwy, Chicago, IL 60612,

USA

Phone: +1 312 947 0398

e-mail: marinos.kontzialis@gmail.com

Marines KONTZIALIS, Mehmet KOCAK

Department of Radiology, Rush University Medical Center, Chicago, IL, USA

How to cite: Kontzialis M, Kocak M. Imaging evaluation of trigeminal neuralgia. J Istanb Univ Fac Dent 2017;51(3 Suppl 1):S62-S68.

Received: 22/02/2017

Accepted:21/03/2017

http://dx.dei.erg/10.17096/jiufd.27242
Table 1. Causes of trigeminal neuralgia by location. The list is not
exhaustive and highlights the major considerations encountered in
clinical practice.

Brainstem            Multiple sclerosis
                     Mass lesion: tumor, cavernous malformation
                     Infection including herpes
                     Infarct
                     Syringobulbia
Cisternal space and  Neurovascular conflict (the most common cause
Meckel's cave        of trigeminal neuralgia)
                     Mass in the cisterns: schwannoma, meningioma,
                     epidermoid
                     Leptomeningeal process: carcinomatosis, lymphoma,
                     leukemia, sarcoidosis, meningitis
                     Skull base mass: chordoma, chondrosarcoma, multiple
                     myeloma, osseous metastasis
                     Gradenigo syndrome
Cavernous sinus      Neoplasms: schwannoma, meningioma, pituitary
                     macroadenoma, lymphoma, nasopharyngeal carcinoma,
                     metastatic disease
                     Tolosa-Hunt syndrome
                     Infection
                     Carotid-cavernous aneurysm/fistula
Extracranial space   Perineural spread of head and neck neoplasm
                     Peripheral nerve sheath tumor
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Author:Kontzialis, Marines; Kocak, Mehmet
Publication:Journal of Istanbul University Faculty of Dentistry
Article Type:Report
Date:Oct 15, 2017
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