Microstructural alterations in trigeminal neuralgia determined by diffusion tensor imaging are independent of symptom duration, severity, and type of neurovascular conflict

Abstract

T rigeminal neuralgia (TN) is characterized by recurrent episodes of intense and lancinating pain localized to the sensory supply areas of the fifth cranial nerve (CN V), which is also known as the trigeminal nerve. 11 The most frequent cause of TN is mechanical irritation of the nerve within a vulnerable zone that extents for about 4 to 5 mm from the point of transition from the peripheral (derived from Schwann cells) to the central myelin (derived from the oligodendroglia) (i.e., transition zone) to the most proximal aspect, where the nerve enters the pons (i.e., root entry zone [REZ]). 24,25,31,32 It is widely believed that direct arterial contact causes pulsatile, repetitive trauma that leads to focal axonal degeneration and demyelination processes within this vulnerable site. 9,13,25 These structural alterations facilitate ephaptic neurotransmissions that cause pain upon common triggers such as chewing or tactile sensations.11 Most frequently, neurovascular compression is caused by a direct anatomical relation with the superior cerebellar artery (SCA) (60%-90%), followed by the anterior inferior cerebellar aBBreViatiONS AD = axial diffusivity; ADC = apparent diffusion coefficient; AICA = anterior inferior cerebellar artery; CE = contrast enhanced; CN = cranial nerve; DTI = diffusion tensor imaging; FA = fractional anisotropy; FIESTA = fast imaging employing steady-state acquisition; MRA = MR angiography; MVD = microsurgical decompression; PICA = posterior inferior cerebellar artery; RD = radial diffusivity; REZ = root entry zone; ROI = region of interest; SCA = superior cerebellar artery; TN = trigeminal neuralgia. OBJectiVe In this prospective study diffusion tensor imaging (DTI) was used to evaluate the influence of clinical and anatomical parameters on structural alterations within the fifth cranial nerve in patients with trigeminal neuralgia (TN) due to neurovascular compression. methOdS Overall, 81 patients (40 men and 41 women; mean age 60 ± 5 years) with typical TN were included who underwent microsurgical decompression. Preoperative 3.0-T high-resolution MRI and DTI were analyzed in a blinded fashion. The respective fractional anisotropy (FA) and apparent diffusion coefficient values were compared with the clinical, imaging, and intraoperative data. This study was approved by the institutional review board, and written informed consent was obtained from all patients. reSultS DTI analyses revealed significantly lower FA values within the vulnerable zone of the affected trigeminal nerve compared with the contralateral side (p = 0.05). The DTI analyses also included 3 patients without clear evidence of neurovascular conflict on preoperative MRI. No differences were seen between arterial and venous compression. Lower FA values were found 5 months after symptom onset; however, no correlation was found with the duration of symptoms or severity of compression. cONcluSiONS DTI analysis allows the quantification of structural alterations, even in those patients without any discernible neurovascular contact o...

Fraction of anisotropy and apparent diffusion coefficient as diagnostic tools in trigeminal neuralgia

“…Other three studies did not find differences in ADC values between affected and unaffected sides of patients and controls [13,24,25]. Concerning only DTI studies about TN caused by NVC, six articles found a significant decrease in FA values [14,17,[22][23][24][25] and two a significant increase in ADC values [17,23] in the affected nerves.The measurement of FA and ADC provides robust values for quantifying the degree of microstructural abnormalities of TGN. Degeneration or damage of white matter tracts is expected to result in reduced FA, owing to the loss of directionality of diffusion and increase in ADC, that is due to diffusivity being averaged in all spatial directions as a result of the loss of myelin and axonal membranes [1].…”

“…Chen et al, Leal et al, and Lummel et al reported a significant elevation in ADC values in the affected sides of patients [7,17,23]. Other three studies did not find differences in ADC values between affected and unaffected sides of patients and controls [13,24,25]. Concerning only DTI studies about TN caused by NVC, six articles found a significant decrease in FA values [14,17,[22][23][24][25] and two a significant increase in ADC values [17,23] in the affected nerves.The measurement of FA and ADC provides robust values for quantifying the degree of microstructural abnormalities of TGN.…”

“…FA describes how much molecular displacements vary in space and is related to the presence of oriented structures [28]. ADC, expressed as square millimeter per second, characterizes the overall mean-squared displacement of molecules and the overall presence of obstacles to diffusion [2, 28].These evidences motivated several studies to examine structural abnormalities in the trigeminal nerve (TGN) of patients with TN using FA [5-7, 9, 10, 13-15, 17, 22-25, 30] and ADC [7,13,17,[23][24][25]. Most of the studies examining FA by comparing the affected and unaffected sides of patients and controls revealed a significant decrease in FA values [5-7, 9, 10, 14, 15, 17, 22-25].…”

“…These evidences motivated several studies to examine structural abnormalities in the trigeminal nerve (TGN) of patients with TN using FA [5-7, 9, 10, 13-15, 17, 22-25, 30] and ADC [7,13,17,[23][24][25]. Most of the studies examining FA by comparing the affected and unaffected sides of patients and controls revealed a significant decrease in FA values [5-7, 9, 10, 14, 15, 17, 22-25].…”

Application of diffusion tensor imaging in detecting microstructural alteration of the trigeminal nerve root in patients with classical trigeminal neuralgia without neurovascular compression

“…MRI was performed on a 3.0-T MRI scanner (Signa HDx; 3T GE Healthcare) using a standardized protocol. [21] Images were obtained using an 8-channel head coil with sensitivity encoding parallel processing capability, with the application of 64 non-collinear directions of diffusion gradients. The sequences and their parameters are summarized in Table 1.…”