Imaging the trigeminal nerve and pons before and after surgical intervention for trigeminal neuralgia

Characteristics and management of the offending veins in microvascular decompression surgery for trigeminal neuralgia

The optimal technique of microvascular decompression (MVD) for trigeminal neuralgia (TN) caused by venous conflict remains unclear. The objectives of this study are to characterize the offending veins identified during MVD for TN and to evaluate intraoperative technique applied for their management. From 2007 till 2019, 308 MVD surgeries were performed in 288 consecutive patients with TN, and in 58 of them, pure venous conflict was identified. In 44 patients, the offending vein was interrupted, as was done for small veins arising from the cisternal trigeminal nerve (CN V) or its root entry zone (REZ) causing their stretching (19 cases), small veins on the surface of REZ (9 cases), transverse pontine vein (TPV) compressing REZ or distal CN V (12 cases), and superior petrosal vein (SPV) using flow conversion technique (4 cases). In 14 other cases, the offending vein was relocated, as was done for the SPV or the vein of cerebellopontine fissure (8 cases), TPV (3 cases), and the vein of middle cerebellar peduncle (3 cases). Complete pain relief after surgery was noted in 49 patients (84%). No one patient experienced major neurological deterioration. Postoperative facial numbness developed in 14 patients (24%), and in 8 of them, it was permanent. In 14 patients, MRI demonstrated venous infarction of the middle cerebellar peduncle, which was associated with the presence of any (P = 0.0180) and permanent (P = 0.0002) facial numbness. Ten patients experienced pain recurrence. Thus, 39 patients (67%) sustained complete pain relief at the last follow-up (median, 48 months), which was significantly associated with the presence of any (P = 0.0228) and permanent (P = 0.0427) postoperative facial numbness. In conclusion, in cases of TN, small offending veins arising from REZ and/or distal CN V and causing their stretching may be coagulated and cut. In many cases, TPV can be also interrupted safely or considered as collateral way for blood outflow. The main complication of such procedures is facial numbness, which is associated with the venous infarction of middle cerebellar peduncle and long-term complete pain relief.

Nerve atrophy in severe trigeminal neuralgia: noninvasive confirmation at MR imaging--initial experience

PURPOSE

To retrospectively evaluate the size of the trigeminal nerve on magnetic resonance (MR) images of patients with unilateral trigeminal neuralgia.

MATERIALS AND METHODS

Institutional review board approval was obtained and informed consent was waived for this HIPAA-compliant study. The sizes of the trigeminal nerves in 31 patients (18 men and 13 women; mean age, 68 years; age range, 44-84 years) with clinically confirmed intractable unilateral trigeminal neuralgia were measured before treatment with gamma knife radiosurgery. Images were analyzed separately by two neuroradiologists who were blinded to the side of the face with symptoms. Coronal projection images were used to determine the diameter and cross-sectional area of the trigeminal nerves at 5 mm from the entry point of the nerve into the pons. Comparisons were made by using a paired t test. Interobserver variability was assessed by using the Pearson correlation coefficient.

RESULTS

The mean diameter of the trigeminal nerve on the symptomatic side was significantly smaller than the mean diameter on the asymptomatic side in 30 of 31 patients (2.11 mm +/- 0.40 [standard deviation] and 2.62 mm +/- 0.56, P < .001, 95% confidence interval: -0.35, -0.67 mm). The mean cross-sectional area on the symptomatic side was significantly smaller than the area on the asymptomatic side in 27 of 31 patients (4.50 mm(2) +/- 1.75 and 6.28 mm(2) +/- 2.19, P < .001, 95% confidence interval: -2.41, -1.16 mm(2)).

CONCLUSION

The results indicate that trigeminal nerve atrophy can be depicted noninvasively in patients with trigeminal neuralgia.

Somatotopic activation in the human trigeminal pain pathway

Functional magnetic resonance imaging was used to image pain-associated activity in three levels of the neuraxis: the medullary dorsal horn, thalamus, and primary somatosensory cortex. In nine subjects, noxious thermal stimuli (46 degrees C) were applied to the facial skin at sites within the three divisions of the trigeminal nerve (V1, V2, and V3) and also to the ipsilateral thumb. Anatomical and functional data were acquired to capture activation across the spinothalamocortical pathway in each individual. Significant activation was observed in the ipsilateral spinal trigeminal nucleus within the medulla and lower pons in response to at least one of the three facial stimuli in all applicable data sets. Activation from the three facial stimulation sites exhibited a somatotopic organization along the longitudinal (rostrocaudal) axis of the brain stem that was consistent with the classically described "onion skin" pattern of sensory deficits observed in patients after trigeminal tractotomy. In the thalamus, activation was observed in the contralateral side involving the ventroposteromedial and dorsomedial nuclei after stimulation of the face and in the ventroposterolateral and dorsomedial nuclei after stimulation of the thumb. Activation in the primary somatosensory cortex displayed a laminar sequence that resembled the trigeminal nucleus, with V2 more rostral, V1 caudal, and V3 medial, abutting the region of cortical activation observed for the thumb. These results represent the first simultaneous imaging of pain-associated activation at three levels of the neuraxis in individual subjects. This approach will be useful for exploring central correlates of plasticity in models of experimental and clinical pain.

Trigeminal neuralgia and other neuropathic pain syndromes of the head and face

Trigeminal neuralgia is the most common craniofacial pain syndrome of neuropathic origin. Although the diagnosis remains based exclusively on history and symptomatology, modern diagnostic techniques, particularly high-resolution magnetic resonance imaging, provides valuable new insight into the pathophysiology of these cases with additional implications for therapeutic strategies. Other neuropathic syndromes affect the trigeminal nerve and warrant different treatments with varied rates of success. Rarely, neuralgias of other cranial nerves mimic trigeminal neuralgia. Finally, it is imperative to distinguish atypical facial pains from these neuropathic syndromes to avoid unsuccessful therapies.

Diagnosis and differential diagnosis of trigeminal neuralgia

Trigeminal neuralgia is a chronic facial pain classified as a neuropathic pain. There is widespread agreement regarding the International Association for the Study of Pain definition of classical idiopathic trigeminal neuralgia as "a sudden, usually unilateral, severe, brief, stabbing, recurrent pain in the distribution of one or more branches of the fifth cranial nerve." However, there are variations in presentation that are less easy to diagnose and an erroneous diagnosis of trigeminal neuralgia is occasionally made. In patients with tumors or multiple sclerosis, trigeminal neuralgia is termed secondary. Currently, clinical manifestations are the mainstay for diagnosis because there are no objective tests to validate the diagnosis. The sensitivity and specificity of these clinical manifestations is reviewed. Magnetic resonance imaging (MRI) and three-dimensional fast-in-flow with steady-state precession MRI are performed to determine the presence of tumors or plaques of multiple sclerosis and to assess possible compressions and deformations of the trigeminal nerve. Their specificity and sensitivity regarding compressions found at the time of surgery is reviewed. Other differential diagnoses for chronic unilateral orofacial pain are discussed.

Microvascular decompression

Microvascular decompression (MVD) remains the only treatment of trigeminal neuralgia that directly addresses the presumed pathogenesis. It is a proven therapy, associated with the longest duration of pain relief while preserving facial sensation. The authors' premise for advocating early MVD is the belief that the disease's natural progression, in the absence of treatment, is toward the development of more atypical features that are refractory to treatment, signifying ongoing neuropathic injury. In an effort to more successfully select candidates for MVD, the authors have incorporated high-resolution magnetic resonance imaging into our preoperative algorithm, since it has proven extremely accurate in defining the neurovascular relations at the trigminal nerve complex. Microvascular decompression can only be recommended when it is performed with low rates of morbidity.