Trigeminal neuralgia and facial nerve paralysis

Abstract

The trigeminal nerve is the largest of the cranial nerves. It provides sensory input from the face and motor innervation to the muscles of mastication. The facial nerve is the cranial nerve with the longest extracranial course, and its main functions include motor innervation to the muscles of facial expression, sensory control of lacrimation and salivation, control of the stapedial reflex and to carry taste sensation from the anterior two-thirds of the tongue. In order to be able adequately to image and follow the course of these cranial nerves and their main branches, a detailed knowledge of neuroanatomy is required. As we are dealing with very small anatomic structures, high resolution dedicated imaging studies are required to pick up normal and pathologic nerves. Whereas CT is best suited to demonstrate bony neurovascular foramina and canals, MRI is preferred to directly visualize the nerve. It is also the single technique able to detect pathologic processes afflicting the nerve without causing considerable expansion such as is usually the case in certain inflammatory/infectious conditions, perineural spread of malignancies and in very small intrinsic tumours. Because a long course from the brainstem nuclei to the peripheral branches is seen, it is useful to subdivide the nerve in several segments and then tailor the imaging modality and the imaging study to that specific segment. This is particularly true in cases where topographic diagnosis can be used to locate a lesion in the course of these nerves.

Imaging the cranial nerves: part II: primary and secondary neoplastic conditions and neurovascular conflicts

“…Primary cranial nerve neoplasms include schwannomas, neurofibromas, hemangiomas, paragangliomas, hamartomas and other exceedingly rare tumors [1,[7][8][9][10].…”

“…It is not uncommon that cranial nerve dysfunction is the first sign of neighboring disease due to compression, perineural spread or metastatic disease. Neurologists, ENT surgeons, ophthalmologists and maxillo-facial surgeons are often confronted with cranial nerve deficits when they first examine a patient, and cranial nerve dysfunction is a common indication for imaging [1][2][3].…”

Imaging the hypoglossal nerve

“…The principles of designing a MR protocol for the hypoglossal nerve follow the same basic principles as for the other cranial nerves [7,[13][14][15]38] (Table 2).…”

What if you cannot see the target? Two case studies of atlas-to-patient registration in trigeminal neuralgia radiosurgery.

“…Both morphological MRI and magnetic resonance angiography (MRA) [19] have been widely proposed to understand the aetiology of the trigeminal neuralgia and plan the appropriate therapeutic strategy. Additionally, CT scans have been suggested to offer complementary information, especially for the bony structures [20] and provide information able to reduce the uncertainty present in the localization of the nerve when using MRI only [21]. Therefore, to localize the trigeminal nerve in functional radiosurgery, two patients affected by trigeminal neuralgia and candidates scheduled to undergo trigeminal radiosurgery by the CyberKnife were imaged with a 3T scanner (TrioTim, Siemens Healthcare, Erlangen, Germany) using several T1-weighted (T1w) and T2-weighted (T2w) pulse sequences with different parameters.…”

“…The objective function was optimized by applying a steepest descent algorithm, which searches for the local optimum solution in the neighbourhood of the initial conditions, which are supposed to be favourable because of the previously applied global and local affine transformations. The regularization factor, as in our previous works [14][15][16][17][18][19][20][21][22], was initially set equal to 0.4, which provided the most accurate matching of the brain structures with a LNR registration error smaller than or equal to the maximum voxel size (mvs) of the datasets to be registered. Different regularization factors were investigated for special cases of dramatic changes in the brain geometry, but the initial value proved to offer the most accurate match…”