Microsurgical Resection of a Giant Trochlear Nerve Schwannoma: 2-Dimensional Operative Video.

We present the case of a 17-year-old male, who complained of a 1-year onset of pulsatile headache, dysphagia, speech changes, and emotional lability. Neuroimaging revealed a large left-sided contrast-enhancing tumor located at the infratentorial space consistent with a large trochlear nerve schwannoma. The tumor was compressing the brainstem, obstructing the outflow of the third and lateral ventricles causing hydrocephalus, and disturbing the cortico-bulbar pathways bilaterally leading to the diagnosis of pseudobulbar palsy. After the patient consented the surgical procedure, he was operated through a subtemporal transtentorial approach placed in the lateral position. A lumbar drain was used for brain relaxation during the procedure and image guidance to define the limits of surgical exposure. A microsurgical technique was used, aiming to preserve the cranial nerves and the vascular structures running through the perimesencephalic cisterns. Gross total resection was achieved and clinical course remained uneventful aside from a transient third nerve palsy. Symptoms improved and the three-month follow-up revealed an almost complete function of the oculomotor nerve (Video 1). Trochlear nerve schwannomas are the rarest variety of the cranial nerve schwannomas. Depending on tumor size, clinical and neuroimaging signs of mass effect and brainstem compression, treatment can be observation, microsurgical resection through cranial base approaches or radiosurgery.1-5.

Effect of inferior oblique myectomy on ocular torsion according to the absence of the trochlear nerve in unilateral congenital superior oblique palsy.

OBJECTIVES: To evaluate the effect of inferior oblique (IO) myectomy on ocular torsion according to the absence of the trochlear nerve in unilateral congenital superior oblique palsy (UCSOP). METHODS: We retrospectively reviewed the clinical data of patients who had been diagnosed with UCSOP and underwent ipsilateral IO myectomy (n = 43). Patients were classified into the present and absent groups according to the absence of the trochlear nerve and superior oblique hypoplasia on magnetic resonance imaging (MRI). For quantitative analysis of ocular torsion, disc-fovea angles (DFA) were collected in both eyes using fundus photographs taken within three months before surgery and one month after surgery. RESULTS: DFA of the paretic eye did not differ according to the absence of the trochlear nerve (9.4±5.6° in the present group vs. 11.0±5.4° in the absent group, p = 0.508). However, the present group had a larger DFA in the non-paretic eye than the absent group (14.1±6.7° in the present group vs. 8.0±5.0° in the absent group, p = 0.003). The change of ocular torsion after IO myectomy in the paretic eye was -5.3±3.7° in the present group and -4.8±3.5° in the absent group, respectively (p = 0.801). In the non-paretic eye, the change in DFA was -1.5±3.0° in the present group, which was larger than that in the absent group (0.7±2.6°, p = 0.047). In the multivariate analysis, the change in DFA was correlated with only the preoperative DFA (standardized ß = -0.617, p<0.001 in the paretic eye, and standardized ß = -0.517, p<0.001 in the non-paretic eye). CONCLUSIONS: In the paretic eye, there was no significant difference in the change of ocular torsion between both groups, whereas in the non-paretic eye, the present group had a larger change in DFA after IO myectomy than the absent group. However, in the multivariable analysis, the change in ocular torsion was significantly correlated with preoperative excyclotorsion but not with the presence of the trochlear nerve itself.

An endoscope-assisted craniometric cadaveric study for the brain stem and the cisternal segment of the trochlear nerve.

Background and purpose: This study analyzed the relationship of trochlear nerve with neurovascular structures using craniometric measurements. The study was aimed to understand the course of trochlear nerve and minimize the risk of injury during surgical procedures. Methods: Twenty trochlear nerves of 10 fresh cadavers were studied bilaterally using endoscopic assistance through the view afforded by the lateral infratentorial-supracerebellar, and the combined presigmoid-subtemporal transtentorial approaches. Trochlear nerves were exposed bilaterally taking seven parameters into consideration: the distance between the cisternal segment of trochlear nerve and vascular structures (superior cerebellar artery/SCA; posterior cerebral artery/PCA), the origin of the trochlear nerve in the brain stem, the angle in the level of tentorial junction, length, diameter, and length of nerve in the cisternal segment. Results: We identified the brain stem and cisternal segments of the trochlear nerve. The lateral infratentorial supracerebellar approach allowed the exposure of the cisternal segments (crural and ambient cisterns), including the origin of the nerve in the brain stem. The combined presigmoid-subtemporal transtentorial approaches provided visualization of the cisternal segment of the nerve and the free edge of the tentorium. In this study, the mean length and width of the trochlear nerve in the cisternal segment were 30.3 and 0.74 mm, respectively. Length of the trochlear nerve from its origin to its dural entrance was 37.2 mm, tentorial dural entrance angle of the trochlear nerve and exit angle of the trochlear nerve from the brain stem were 127.0 degrees and 54 degrees, PCA to trochlear nerve in mid ambient cistern and SCA to trochlear nerve in mid ambient cistern were 7.3 mm and 6.8mm. Conclusion: Trochlear nerve is vulnerable to injury during the surgical procedures. Therefore, it is necessary to have a sufficient knowledge of the anatomy of cisternal segment and its relationship with adjacent neurovascular structures. The anatomical and craniometric data can be helpful in middle and posterior fossa surgery in minimizing the potential injury of the trochlear nerve.

Surgical Technique and Nuances of Resection of a Trochlear Schwannoma: Operative Video.

Cranial nerve schwannomas accounts for around 8% of all benign intracranial tumors, arising most commonly from the vestibular nerve, followed by the trigeminal nerve and other lower cranial nerves. However, trochlear schwannoma in a patient without neurofibromatosis-2 are extremely rare and to date, fewer than 100 cases have been reported in the literature. They are either asymptomatic or present with ophthalmologic or neurologic symptoms. Diplopia is the most common initial symptom. As the tumor grows, it can compress the surrounding brainstem and other cranial nerves, causing neurologic symptoms. Asymptomatic lesions are detected incidentally following imaging for some other reason. There are no clear guidelines for the management of these tumors. In general, small asymptomatic tumors are closely observed by serial imaging and symptomatic or larger tumors are managed by surgical excision and/or stereotactic radiosurgery.1-7 Here we present a 41-year-old female patient with incidentally detected left trochlear schwannoma during the follow-up magnetic resonance imaging (MRI) scans. She was followed up regularly with multiple repeat MRI. Recently she started complaining of occasional headaches, and MRI showed a left peimesencephalic cistern tumor causing mass effect on the ipsilateral midbrain. There was also significant brainstem edema. Hence she underwent left retromastoid suboccipital craniectomy, lateral supracerbellar approach, and complete excision of the tumor. Postoperatively the patient had an uneventful recovery without any new neurologic deficits. At 6 months' follow-up the patient is doing well.

Surgical Treatment of Trochlear Nerve Schwannomas: Case Series and Systematic Review.

BACKGROUND AND OBJECTIVE: Cranial nerve schwannomas almost always arise from sensory or mixed nerves. Motor cranial nerves, such as the trochlear nerve, are rarely associated with schwannomas. No consensus has yet been made for surgical intervention because of the low number of reported cases of trochlear nerve schwannomas. This study comprises a systematic review of the literature and our experience for surgically treated trochlear nerve schwannomas. METHODS: Three databases (Web of Science, PubMed, and Cochrane Library) were searched without date restrictions. Studies were included if they were published in the English literature and presented patients of any age who underwent surgical treatment for trochlear schwannoma. Data extracted from the included studies were combined with our experience. RESULTS: Forty-one studies, presenting 43 patients, met the inclusion criteria. The total number of patients was 45 after our experience was added. The most common symptoms were diplopia (62.2%), headache (46.7%), and motor weakness (37.8%). Mean age during the diagnosis was 45.1 years. Although the subtemporal transtentorial approach (n = 14) is the most preferred method, its application has decreased in recent years. In the last decade, the lateral suboccipital approach (n = 11) has gained popularity. Residual postoperative trochlear nerve deficit was detected in 81% of patients. The probability of neurologic deficit was not statistically associated with tumor volume (P = 0.914), location (P = 0.669), or resection rate (P = 0.554). CONCLUSIONS: Although trochlear schwannomas are rare and their treatment involves challenges, total resection with the proper approach provides the most desirable results.

Trochleaectomy: An Effective Treatment of Trochlear Pain in Monocular Patients.

BACKGROUND: Conventional treatment options for trochlear pain arising from trochleitis or primary trochlear headache include oral anti-inflammatory medications and/or local injection of corticosteroids and local anesthetic. Trochleaectomy is an additional option to consider for monocular patients with intractable trochlear pain. METHODS: We report 3 patients undergoing trochleaectomy for refractory trochlear pain syndromes. RESULTS: Trochleaectomy resulted in resolution of their periocular discomfort. CONCLUSIONS: Trochleaectomy is an effective procedure to treat trochlear pain syndrome in functionally monocular patients.

Innervation of Orbicularis Oculi by Trochlear Nerve: Word of Caution.

BACKGROUND: Neurosurgeons who operate in and around the pathway of the ocular nerves should have good knowledge of not only their normal anatomy but also their variations. CASE DESCRIPTION: During routine dissection of the orbits in an adult cadaver, an aberrant branch of the right trochlear nerve continued on to innervate the orbicularis oculi muscle. In this case, the trochlear nerve also provided a branch to the supratrochlear nerve. CONCLUSIONS: Surgeons who operate along the pathway of the trochlear nerve such as the cavernous sinus should be aware of such an anatomic variant in order to avoid unwanted complications such as weakness of the orbicularis oculi muscle.

Transventricular Transvelar Approach to Trochlear Nerve Schwannoma: Novel Technique to Lesions of Inferior Pineal Region.

OBJECTIVES: The schwannoma of the trochlear nerve is rare and originates mostly from the distal parts in the interpeduncular cistern. A lesion on the proximal segment in the inferior pineal region is extremely rare. Because of the rarity of the disease, the surgical approach to this region for the resection of trochlear nerve schwannoma has not been well documented in the literature. We herein describe a novel approach to successfully resect the trochlear nerve schwannoma. METHODS: A 12-year-old boy presented with occipital headache, abnormal gait, and disturbed conjoined eye movement. He was diagnosed with a lesion in the inferior pineal region compressing the superior medullary velum into the roof of the fourth ventricle. A bilateral midline suboccipital craniotomy was performed, and the fourth ventricle was exposed. The lesion was approached through the fourth ventricle superior medullary velum (transventricular transvelar approach). The lesion was totally resected, and his histopathology examination revealed trochlear schwannoma. RESULTS: The patient's symptoms resolved, and he had no recurrence at 12-year follow-up with normal eye movement and vision. CONCLUSION: The transventricular transvelar approach is feasible and safe to treat a lesion of the lower part of the pineal region being pushed through the superior medullary velum.

Supratrochlear Neuralgia: A Prospective Case Series of 15 Patients.

OBJECTIVE: The aim of this study was to describe clinical features unique to supratrochlear neuralgia. BACKGROUND: The supratrochlear nerve supplies the medial aspect of the forehead. Due to the intricate relationship between supraorbital and supratrochlear nerves, neuralgic pain in this region has been traditionally attributed to supraorbital neuralgia. No cases of supratrochlear neuralgia have been reported so far. METHODS: From 2009 through 2016, we prospectively recruited patients with pain confined to the territory of the supratrochlear nerve. RESULTS: Fifteen patients (13 women, 2 men; mean age 51.4 years, standard deviation 14.9) presented with pain in the lower paramedian forehead, extending to the eyebrow in two patients and to the internal angle of the orbit in another. Pain was unilateral in 11 patients (six on the right, five on the left), and bilateral in four. Six patients had continuous pain and nine described intermittent pain. Palpation of the supratrochlear nerve at the medial third of the supraorbital rim resulted in hypersensitivity in all cases. All but one patient exhibited sensory disturbances within the painful area. Fourteen patients underwent anesthetic blockades of the supratrochlear nerve, with immediate relief in all cases and long-term remission in three. Six of them had received unsuccessful anesthetic blocks of the supraorbital nerve. Five patients were treated successfully with oral drugs and one patient was treated with radiofrequency. CONCLUSIONS: Supratrochlear neuralgia is an uncommon disorder causing pain in the medial region of the forehead. It may be differentiated from supraorbital neuralgia and other similar headaches and neuralgias based on the topography of the pain and the response to anesthetic blockade.

Pineal region schwannoma arising from the trochlear nerve.

Schwannomas arising from the trochlear nerve are very rare and to our knowledge, less than 35 histologically documented cases have been reported in the literature. There are no reports of a schwannoma in the pineal region. We report a 24-year-old woman who underwent a para-occipital trans-tentorial approach and gross total excision of a pineal region schwannoma arising from the trochlear nerve. This is the first such reported case.

Surgical Outcomes of Inferior Oblique Myectomy in Unilateral Congenital Superior Oblique Palsy with or without Trochlear Nerve.

OBJECTIVES: To compare the surgical outcomes of inferior oblique (IO) myectomy in congenital superior oblique palsy (SOP) according to the presence of the trochlear nerve identified with high-resolution MRI. DATA EXTRACTION: Forty-one congenital SOP patients without a trochlear nerve (absent group) and 23 patients with a trochlear nerve (present group) who underwent IO myectomy as the primary surgical treatment were retrospectively reviewed. "Motor success" was defined as postoperative ipsilateral hypertropia ≤ 4 prism diopter (PD). "Head tilt improvement" was regarded as postoperative angle of head tilt < 5 degrees (°). Success rates for motor alignment and head tilt improvement, cumulative probabilities of success, and factors influencing surgical responses were evaluated. RESULTS: The cumulative probabilities of motor success at 2 years after IO myectomy were 92% in patients with a trochlear nerve and 86% in patients without a trochlear nerve (P = 0.138). The cumulative probabilities of undercorrection and recurrence of hypertropia after 2 years were 0% in the present group versus 21% in the absent group (P = 0.014). The cumulative probabilities of persistent head tilt after 2 years were 14% in the present group and 20% in the absent group (P = 0.486). A younger age at operation was associated with reduced probabilities of motor success and head tilt improvement (P = 0.009, P = 0.022 respectively). A greater preoperative angle of head tilt was associated with persistent head tilt after surgery (P = 0.038). CONCLUSIONS: Congenital SOP without a trochlear nerve had a higher risk of hypertropia undercorrection after IO myectomy compared to patients with a trochlear nerve. A younger age at operation and larger preoperative head tilt was related to poor outcomes.

Microsurgical anatomy of the trochlear nerve.

The trochlear nerve is the cranial nerve with the longest intracranial course, but also the thinnest. It is the only nerve that arises from the dorsal surface of the brainstem and decussates in the superior medullary velum. After leaving the dorsal surface of the brainstem, it courses anterolaterally around the lateral surface of the brainstem and then passes anteriorly just beneath the free edge of the tentorium. It passes forward to enter the cavernous sinus, traverses the superior orbital fissure and terminates in the superior oblique muscle in the orbit. Because of its small diameter and its long course, the trochlear nerve can easily be injured during surgical procedures. Therefore, precise knowledge of its surgical anatomy and its neurovascular relationships is essential for approaching and removing complex lesions of the orbit and the middle and posterior fossae safely. This review describes the microsurgical anatomy of the trochlear nerve and is illustrated with pictures involving the nerve and its surrounding connective and neurovascular structures.

Microvascular decompression for superior oblique myokymia: case report.

BACKGROUND: Superior oblique myokymia (SOM) is a rare disorder in which the patient suffers episodic uniocular torsional eye movement associated with diplopia and oscillopsia . Although the pathophysiology has been narrowed down to erratic discharge of the trochlear nerve, yet the exact etiology remains unclear; a handful of cases have been described in association with an identifiable space occupying lesions or dural AV fistulae. Neurovascular compression theory has been postulated in the early 1980s and to our knowledge, very few reports exist in the literature accrediting this hypothesis in the pathogenesis of superior oblique myokymia. CASE REPORT: We report a case of successful resolution of severe medication refractory SOM following microvascular decompression of the trochlear nerve. The clinical response has been sustained for a follow-up period of 18 months to date. CONCLUSION: Microvascular decompression may be considered as a definitive and least destructive surgical option for the treatment of medication refractory superior oblique myokymia.

Supratrochlear and supraorbital nerves: an anatomical study and applications in the head and neck area.

BACKGROUND: This article elucidates the anatomical details of the course and territory of the supraorbital (SO) and supratrochlear (ST) nerves. Possible applications of the SO and ST nerves for sensory nerve transfer are also examined. METHODS: The dissection of 3 fresh cadaver heads (6 hemifaces) was performed. In each hemiface, the ST and SO nerves were identified. The following data were recorded: 1) number of branches, 2) skin boundaries, 3) communicative branches, and 4) branch length. The feasibility of specific nerve-transfer procedures was also examined. RESULTS: In 4 hemifaces the SO nerve exited from the SO notch and in 2 hemifaces from the SO foramen. The position was lateral to the midline, with a mean distance of 1.93 cm. In all dissections, a maximum of 4 SO branches (range 2-4) were identified. The ST nerve exited the orbital rim medial to the SO nerve, and lateral to the midline with a mean distance of 0.866 cm. The mean distance between the SO and ST nerves at the level of the SO rim was 1.06 cm. In 5 of 6 hemifaces, several sub-branches emerged from the main trunk of the ST nerve. In 1 hemiface the ST nerve was divided in 2 main branches. CONCLUSIONS: The data presented in the current study are in agreement with previous anatomical studies. Both ST and SO nerves can be used as sensory nerve donors in the head and neck area for numerous expanding applications.

The extended subtemporal transtentorial approach: the impact of trochlear nerve dissection and tentorial incision.

The subtemporal transtentorial approach provides excellent exposure of the incisural space. Incision of the tentorium improves access to the interpeduncular cistern, basilar artery, and rostral ventral pons. Description of the starting and termination points of the tentorial incision has varied greatly. We assessed the impact on surgical exposure of freeing the trochlear nerve (TN) from its dural canal (DC) in addition to dividing and retracting the tentorium. A subtemporal approach was performed on 10 hemispheres of cadaveric specimens. Following exposure of the middle tentorial incisura, the TN is dissected from its DC over a few millimeters. Two retraction sutures are placed along the tentorial edge, posterior to the TN entrance in its DC. The tentorial incision is started between the sutures. Dissection of TN from its DC continues for a short distance. The tentorial incision is extended straight up towards the superior petrosal sinus. Dissection of the TN DC continues anteriorly, up to its entry into the cavernous sinus. The tentorial incision can then be extended, just over the entrance to Meckel's cave, and the flap reflected far anterolateraly. Using this technique, the exposure of the interpeduncular cistern and its content increased by a mean of 8.2 mm (standard deviation [SD] 3.9 mm) in the anteroposterior axis and by 5.5mm (SD 1.9 mm) in the rostrocaudal axis. Tentorial incision following dissection of the TN from its DC optimizes reflection of the tentorium flap anterolateraly, maximizes the exposure, and improves lighting and visibility as well as maneuverability within the interpeduncular and rostral pre-pontine cisterns.

Eyelid and eye movements following fourth to third nerve anastomosis.

A 34-year-old woman presented with brainstem compression from a large third nerve schwannoma although third nerve function was intact. At surgery, preservation of the proximal third nerve was not possible. Because of preexisting amblyopia of the contralateral eye, an attempt was made to surgically reinnervate the affected third nerve. The fourth nerve was divided at its entry into the tentorium and anastomosed to the distal stump of the third nerve. Partial recovery of third function occurred over several months and is still present 6 years later. Successful long-term reinnervation of the third nerve by direct anastomosis with the fourth nerve may be useful when third repair is not possible.

Anatomy of Meckel's cave and the trigeminal ganglion: anatomical landmarks for a safer approach to them.

AIM: Surgical approaches to Meckel's cave (MC) are often technically difficult and sometimes associated with postoperative morbidity. The relationship of surgical landmarks to relevant anatomy is important. Therefore, we attempted to delineate quantitatively their anatomy and the relationships between MC and surrounding structures. MATERIAL AND METHODS: With the aid of a surgical microscope, MC and its contents were studied in 15 formalin-fixed cadaver head specimens. Measurements were made and their relationships were observed. RESULTS: The distance from the zygomatic arch and the lateral end of the petrous ridge to MC was 26.5 and 34.4 mm, respectively. The distance from the arcuate eminence, the facial nerve hiatus, and the foramen spinosum to MC was 16.6, 12.8 and 7.46 mm respectively. The TG lay 5.81 mm posterior to the foramen ovale. The distance from the abducens, trochlear and oculomotor nerves to the trigeminal ganglion was 1.87, 5.53 and 6.57 mm respectively. The distance from the posterior and the anterior walls of the sigmoid sinus to the trigeminal porus was 43.6 and 33.1 mm respectively. The trigeminal porus was on average 7.19 mm from the anterior wall of the internal acoustic meatus. CONCLUSION: The anatomical landmarks as presented herein regarding MC may be used for a safer skull base approach to the region.

Location of the abducent nerve within the cavernous sinus.

AIM: Knowing the distance between the superior and inferior border of Parkinson's triangle and the location of the abducent nerve within the cavernous sinus is important to decrease the complications which may occur during surgery. We aimed to investigate the cavernous sinus to decrease the complications that may occur during surgery to this area. MATERIAL AND METHODS: Fifty MRIs without pituitary gland abnormality were chosen for radiological assessment of CS. These images were from 18 males and 32 females, with ages ranging from 9 to 58 years and a median age of 28 years. We evaluated structures within and on the lateral wall of the cavernous sinus (especially Parkinson's triangle) with magnetic resonance imaging. The position of the abducent nerve and its level according to the cranial nerves running close the lateral wall were examined. RESULTS: At the level of pituitary stalk, the distance between the trochlear nerve and the ophthalmic nerve ranged from 1 to 4 mm bilaterally. The abducent nerve was located between the trochlear and the ophthalmic nerves in 30% cases bilaterally. CONCLUSION: The knowledge of the position of the abducent nerve will provide a great benefit in minimizing the rate of complications that may occur during the resection of tumors of the cavernous sinus.