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.

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 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.

Hourglass cystic schwannoma of the trochlear nerve

Cranial nerves' schwannomas most commonly arise from the vestibular nerve. Involvement of other cranial nerves, in absence of neurofibromatosis, is extremely rare. A case of a pathology proven trochlear nerve schwannoma, with internal cystic components, in a patient with isolated right superior oblique muscle palsy, is described. Only 67 cases of such entity have been previously reported in the literature.

[Neurinomas of the trochlear nerve]

Trochlear neurinomas are extremely rare. This paper presents 2 cases of surgically treated trochlear neurinomas. In the first case, the tumor occupied the lateral part of the tentorial notch was removed via retromastoidal approach. In the other case, neurinoma was located in the posterior parts of the tentorial notch and removed via paramedian subtentorial supracerebellar approach.

Acute superior oblique palsy in monkeys: I. Changes in static eye alignment

PURPOSE

To investigate immediate and long-term changes in static ocular alignment with acute acquired superior oblique palsy (SOP) in monkeys.

METHODS

The trochlear nerve was severed intracranially in two rhesus monkeys. After the surgery, the paretic eye was patched for 6 to 9 days, and then binocular viewing was allowed. Three-axis eye movements (horizontal, vertical, and torsional) were measured with binocular, dual search coils. Eye movements were recorded over a +/-20 degrees horizontal and vertical range of fixations before the lesion and then, beginning the first day after surgery. Changes in alignment with +/-30 degrees head tilt were also studied.

RESULTS

The main findings were (1) misalignment (10-12 degrees vertical in adduction, down; 10-12 degrees torsional in abduction, down); (2) changes in vertical deviation (VD) with head tilt (Delta 2-6 degrees with left versus right 30 degrees tilt); and (3) changes in comitance and VD over time. During the early postlesion period, before binocular viewing was allowed, VD decreased and comitance improved. Once binocular viewing was allowed, VD increased and comitance worsened.

CONCLUSIONS

Rhesus monkeys with induced SOP show a characteristic pattern of misalignment that helps define the ocular motor signature of acute denervation of the superior oblique muscle. The animals also showed striking changes over time in the amount and comitance of the vertical misalignment that depended on whether viewing was monocular or binocular, suggesting a role for proprioception in adaptation to misalignment with habitual monocular viewing.

Intraorbital Surgery for Trigeminal Neuralgia

PURPOSE

First-division trigeminal neuralgia, or tic douloureux refractory to medications, presents problems to the surgeon because of the desirability of preserving corneal sensation. A new operation is described that may provide longer duration of pain relief than conventional supraorbital neurectomy, with preservation of the corneal reflex.

METHODS

Four patients underwent resection of the supratrochlear and supraorbital nerves within the orbit accessed from an upper eyelid skin crease incision.

RESULTS

Three patients with typical idiopathic trigeminal neuralgia involving branches of the frontal nerve are without pain 22 to 25 months after surgery. The final patient with atypical pain had no improvement after the procedure. Frontal nerve distribution anesthesia is present in all patients. Postoperative ptosis resolved in all patients within 4 months of surgery.

CONCLUSIONS

This procedure should be added to the treatment options for patients with first-division trigeminal neuralgia. By avoiding injury to the trigeminal root and ganglion, this surgery carries no risk of facial motor dysfunction, dysthesia, and/or anesthesia in the other trigeminal branches including corneal anesthesia.

Proposed Treatment Strategy for Cavernous Sinus Meningiomas: A Prospective Study

OBJECTIVE:

To establish a safe and effective treatment strategy for cavernous sinus (CS) meningiomas, we prospectively analyzed the outcome of a treatment protocol combining surgery and radiosurgery during the past 7 years.

METHODS:

Tumors confined to the CS and distant from the optic apparatus and the brainstem were treated with radiosurgery alone. Tumors attached to or compressing the optic apparatus and brainstem and that were larger than 3 cm in mean diameter, extended into the multiple cranial fossae, and were suspected of being malignant were treated with combined nonradical microsurgery and radiosurgery.

RESULTS:

In accordance with this treatment protocol, 40 patients aged 26 to 72 years (median, 51 yr) with primary (n = 27) or recurrent (n = 13) CS meningiomas (volume range, 0.9–39.3 cm3; median volume, 5.4 cm3) were treated with combined surgery and radiosurgery (n = 23) or radiosurgery alone (n = 17). During radiosurgery, 12 to 18 Gy (median, 16 Gy) was delivered to the tumor margin. The follow-up period ranged from 14 to 79 months (median, 47 mo). The actuarial tumor control rate was 94.1% at 5 years. The improvement of cranial nerve function was significantly frequent in patients with primary CS meningiomas (P< 0.05). Permanent cranial nerve dysfunction was significantly frequent in patients with tumors compressing the brainstem or smaller than 10 cm3 (P< 0.05). All 36 patients with a pretreatment Karnofsky Performance Scale score of 90 or more maintained the same range after treatment.

CONCLUSION:

Proper combination of microsurgery and radiosurgery for CS meningiomas provides excellent growth control with favorable functional state. Outcomes were better when this protocol was adopted at the initial diagnosis for patients with smaller tumors that did not compress the brainstem.

Cystic schwannoma of the anterior tentorial hiatus. Case report and review of the literature

Intracranial schwannomas not arising from the facial, trigeminal, or vestibular nerves in the absence of neurofibromatosis are extremely rare. We report a case of a schwannoma arising in the region of the anterior tentorial hiatus and posterior cavernous sinus. A 17-year old girl presented with headaches and intermittent diplopia. An MRI of the brain revealed a heterogeneously enhancing mass adjacent to the free edge of the tentorium, superior to the cerebellopontine angle. An orbitozygomatic pterional craniotomy was done with complete resection of the tumor. Postoperatively, the patient remained neurologically intact. The clinical presentation and treatment of schwannomas arising in this location are discussed.

Neurotization of oculomotor, trochlear and abducent nerves in skull base surgery

OBJECTIVE

To anatomically reconstruct the oculomotor nerve, trochlear nerve, and abducent nerve by skull base surgery.

METHODS

Seventeen cranial nerves (three oculomotor nerves, eight trochlear nerves and six abducent nerves) were injured and anatomically reconstructed in thirteen skull base operations during a period from 1994 to 2000. Repair techniques included end-to-end neurosuture or fibrin glue adhesion, graft neurosuture or fibrin glue adhesion. The relationships between repair techniques and functional recovery and the related factors were analyzed.

RESULTS

Functional recovery began from 3 to 8 months after surgery. During a follow-up period of 4 months to 6 years, complete recovery of function was observed in 6 trochlear nerves (75%) and 4 abducent nerves (67%), while partial functional recovery was observed in the other cranial nerves including 2 trochlear nerves, 2 abducent nerves, and 3 oculomotor nerves.

CONCLUSIONS

Complete or partial functional recovery could be expected after anatomical neurotization of an injured oculomotor, trochlear or abducent nerve. Our study demonstrated that, in terms of functional recovery, trochlear and abducent nerves are more responsive than oculomotor nerves, and that end-to-end reconstruction is more efficient than graft reconstruction. These results encourage us to perform reconstruction for a separated cranial nerve as often as possible during skull base surgery.

The microsurgical anatomy of the cisternal segment of the trochlear nerve, as seen through different neurosurgical operative windows

OBJECTIVE

To describe the anatomy of the cisternal segment of the trochlear nerve as seen through different neurosurgical approaches.

METHODS

The cisternal course of ten trochlear nerves was observed in five cadaveric embalmed heads, through the view afforded by the median infratentorial-supracerebellar, the extreme-lateral infratentorial-supracerebellar, and the combined presigmoid-subtemporal transtentorial approaches. The relationships of the trochlear nerve with the surrounding neuro-vascular structures were analyzed.

RESULTS

We identified 3 segments of the cisternal trochlear nerve: quadrigeminal, ambient and tentorial. The median infratentorial-supracerebellar approach allowed exposure of the quadrigeminal segment, including the origin of the nerve. The extreme-lateral supracerebellar and the combined presigmoid-subtemporal transtentorial approaches provided visualization of the ambient and tentorial segments of the nerve. The tentorial segment runs in a dural canal contained in the free edge of the tentorium, surrounded by its own arachnoidal sleeve.

CONCLUSION

The trochlear nerve is a very delicate structure that can be easily injured during approaches to the tentorial incisura. Accurate knowledge of its anatomy as seen through different operative windows is helpful in maintaining its integrity during surgery.

Infratentorial lateral supracerebellar approach for trochlear nerve schwannoma

Schwannomas of the trochlear nerve are very rare. Only 25 cases without associated neurofibromatosis were reported in the literature, only 15 of which were surgically verified. We report an unusual case of a 31-year-old man who presented with isolated unilateral trochlear nerve palsy due to a left sided trochlear nerve schwannoma. The tumor was totally resected without additional morbidity using an infratentorial lateral supracerebellar approach.

[New view on the causes and treatment of Brown's syndrome]

The cause of the Brown's syndrome has so far been assigned to changes in the tendon sheath. Mühlendyck has proved that in Brown's syndrome patients the tendon sheath is regular whereas the symptoms are caused by changes in muscle obliquus superior or in the trochlea area. Resection of the irregular structures results in a normalisation of the active and passive elevation in adduction. 18 patients have been operated at our department according to the Mühlendyck method. Early postsurgical observations suggest positive results.

Surgically created fourth-third cranial nerve communication: temporary success in a child with bilateral third nerve hamartomas. Case report

Shortly after birth, an otherwise healthy infant developed eye deviation and ptosis due to a hamartomatous lesion of the interpeduncular segment of the right oculomotor nerve. The left nerve became similarly involved when the child was 1.5 years of age. Direct nerve repair was not possible. Instead, the trochlear nerve was divided and its proximal end was attached to the distal end of the third nerve. Elevation of the upper eyelid and partial adduction of the eye developed gradually over the ensuing 3 to 5 months. Both functions were lost after an additional 2 months, presumably as a result of tumor recurrence or neuroma formation. This case report shows that surgically created fourth-third cranial nerve communication is feasible and may merit consideration under similar circumstances.

Relationships of the cisternal segment of the trochlear nerve

OBJECT

The cisternal portion of the trochlear nerve (fourth cranial nerve) can easily be injured during intracranial surgical operations. To help minimize the chance of such injury by promoting a thorough understanding of the anatomy of this nerve and its relationships to surrounding structures, the authors present this anatomical study.

METHODS

In this study, in which 12 cadaveric heads (24 sides) were used, the authors describe exact distances between the trochlear nerve and various surrounding structures. Also described are relatively safe areas in which to manipulate or enter the tentorium, and these are referenced to external landmarks.

CONCLUSIONS

This information will prove useful in planning and executing surgical procedures in and around the free edge of the tentorium cerebelli.

Trochlear nerve schwannomas occurring in patients without neurofibromatosis: case report and review of the literature

OBJECTIVE AND IMPORTANCE

Despite their predilection for sensory nerves, intracranial schwannomas have been reported in a number of mixed and purely motor cranial nerves, especially in association with Type 2 neurofibromatosis. We report the rare occurrence of a trochlear nerve schwannoma in a patient without neurofibromatosis and review 17 other case reports from the literature.

CLINICAL PRESENTATION

A 35-year-old woman presented with an 8-week history of evolving left hemiparesis, bilateral bulbar paresis, and out-of-character emotional lability.

INTERVENTION

She underwent a left temporal craniotomy and a subtemporal, transtentorial approach to the tentorial hiatus, with complete excision of a cisternal trochlear nerve schwannoma.

CONCLUSION

Postoperative complications included temporary oculomotor and abducens nerve palsies and temporary right hemiparesis and mild expressive dysphasia, which were resolved at 23-month follow-up. Preoperative symptoms and signs completely resolved, but a postoperative complete trochlear nerve palsy required inferior oblique myectomy for correction of diplopia. A review of the literature showed no preoperative trochlear nerve involvement in at least 45% of cases. The tumor is isointense on T1- and T2-weighted magnetic resonance images and enhances brightly with gadolinium. The most frequently used approach for surgical excision is the subtemporal approach, and the tumor is almost always totally excised. Long-term follow-up suggests recovery of preoperative deficit, and persisting or new trochlear nerve palsy is the rule.

Cystic trochlear nerve neurinoma

A case of a cystic neurinoma of the trochlear nerve, originally interpreted as an intrinsic brainstem lesion, is presented. The history of the disease, its clinical picture and surgical treatment are described in detail.

Superior oblique luxation and trochlear luxation as new concepts in superior oblique muscle weakening surgery

PURPOSE

We used superior oblique luxation and trochlear luxation as new surgical procedures to treat acquired Brown's syndrome and superior oblique muscle overaction.

METHODS

We studied nine patients (11 eyes) who underwent trochlear surgery between 1988 and 1993. Four patients had acquired Brown's syndrome and five had superior oblique muscle overaction. In five patients (six eyes) the trochlea was incised to luxate the superior oblique tendon out of the trochlea. In four patients (five eyes) the trochlea was luxated out of its fossa via a periosteal approach without opening the trochlea itself.

RESULTS

The mean follow-up was 18 months (range, nine to 33 months). Postoperatively, eight patients showed subjective and objective improvement. One patient with painful traumatic acquired Brown's syndrome had no objective improvement but obtained relief of pain.

CONCLUSIONS

These new techniques are a successful alternative in the treatment of acquired Brown's syndrome and superior oblique muscle overaction.

Transcranial approach to the orbit: microsurgical anatomy

An anatomical study of three microsurgical intraorbital routes to the optic nerve and orbital apex, which can be reached through a fronto-orbital craniotomy, was conducted on cadaver specimens. The structures that could be exposed via the medial, central, or lateral approaches directed through the orbital roof were defined. The medial approach, directed through the space between the superior oblique and the levator muscles, provides good access to all parts of the intraorbital optic nerve. The central approach, between the levator and the superior rectus muscles, provides the shortest route to the optic nerve. Two variants of the central approach were examined. In the first, the levator muscle and frontal nerve are retracted medially and the superior rectus muscle laterally. This variant provides access to only the midportion of the intraorbital segment of the optic nerve. In the second variant, the frontal nerve is retracted laterally together with the superior rectus muscle. This variant provides access to the posterior two-thirds of the intraorbital portion of the optic nerve. The lateral approach is directed between the levator and lateral rectus muscles. This approach also has two variants, depending on whether the superior ophthalmic vein is retracted medially or laterally. The variant in which the superior ophthalmic vein is retracted medially with the levator and superior rectus muscles provides access to the lateral side of the optic nerve except in the region adjacent to the superior orbital fissure. The variant in which the superior ophthalmic vein is retracted laterally together with the lateral rectus muscle provides excellent access to the optic nerve in the region of the superior orbital fissure. It is an ideal approach for lesions that involve both the cavernous sinus and orbit.

Intraoperative adjustable suture surgery for bilateral superior oblique palsy

BACKGROUND

The modified Harada-Ito procedure has been reported to be an effective treatment for correction of cyclotorsion in bilateral superior oblique palsy. However, there are no reports regarding its use in intraoperative adjustable suture surgery.

METHODS

The authors performed a retrospective study of 12 patients with traumatic bilateral superior oblique palsy who were classified as having either symmetric or asymmetric palsy according to the symmetry of the alternate hyperdeviation on side gazes. Cyclotorsion and vertical and horizontal deviation in the nine diagnostic positions were measured preoperatively and postoperatively.

RESULTS

Of the 12 patients, 6 were determined to have symmetric palsy and 6 asymmetric palsy. Intraoperative adjustable suture surgery with the modified Harada-Ito procedure was performed bilaterally in the six patients with symmetric palsy and unilaterally in those with asymmetric palsy. The median measured value of extorsion in the primary position was reduced from 14.5 degrees to 2.5 degrees in patients with symmetric palsy and from 9.5 degrees to 2.0 degrees in those with asymmetric palsy. In downgaze, some degree of residual extorsion remained, and there was no significant change in esodeviation after surgery. In five patients with symmetric palsy and in all of those with asymmetric palsy, normal single binocular vision in the primary position but did not that in downgaze was restored after surgery.

CONCLUSION

Intraoperative adjustable suture surgery is an effective treatment in correcting torsion, but may not be as effective for esodeviation in downgaze.

Trochlear nerve schwannomas: a case report and literature review

Trochlear nerve sheath tumours are extremely uncommon, only six cases diagnosed during life having been presented previously. In none of these earlier cases were magnetic resonance imaging studies obtained. We report here upon the clinical presentation, surgical management and post-operative course of a case where the diagnosis was suspected pre-operatively from MRI studies. The radiological appearances are described, together with a review of all previously published accounts of this rare tumour.

Pituitary apoplexy presenting as multiple ocular nerve palsies of sudden onset

An acromegalic patient with pituitary apoplexy presented with multiple ocular nerve palsies with full visual fields. High resolution CT confirmed a pituitary tumour. We believe this clinical combination to be unique.

'V' esotropia and excyclotropia after surgery for bilateral fourth nerve palsy

Six patients had residual diplopia at near in the downgaze position after surgery for bilateral fourth nerve palsy. They all showed a large excyclotropia in the downgaze position that was associated with a "V"-pattern esotropia and could not fuse in the reading position because of the size of the excyclotropia. They were treated with bilateral recessions of the inferior recti, which resulted in an expansion of the single binocular field of vision in downgaze, with an elimination of diplopia in the reading position. None experienced a deterioration in their alignment in the primary position.

Reconstruction of the third through sixth cranial nerves during cavernous sinus surgery

Sixteen reconstruction procedures of the third through sixth cranial nerves were carried out in 14 patients during operations on 149 tumors involving the cavernous sinus. A direct end-to-end anastomosis was performed in five nerves, whereas in 11 cases the nerve stumps were bridged by means of an interposing nerve graft. The sixth cranial nerve was most frequently reconstructed (nine cases). In four cases, the fifth nerve or root was repaired. The third nerve was reconstructed in two patients, and the fourth nerve was repaired in only one case. Recovery of function, either partial or complete, was observed in 13 nerves: the third in two instances, the fourth in one, the fifth in three, and the sixth in seven. No return of function occurred in three nerves. In patients with a successful recovery of cranial nerve function, either binocular function or the cosmetic result was improved. These results suggest that repair of the third through sixth cranial nerves injured during surgery should be pursued in suitable patients.

Successful outcome following anastomosis of a severed trochlear nerve in the middle fossa

Complete return of function has been obtained following neurosurgical repair of a trochlear nerve inadvertently divided during the clipping of a basilar tip aneurysm. To date this is the second case reported in the literature. The technique of repair and the method of recording the return of function is discussed.

Cryptic angioma in the trochlear nerve. Excision of the invaded portion and successful repair with an autologous graft: case report

Cryptic angiomas, which are intrinsic to cranial nerves, are uncommon. Such lesions involving the trochlear nerve have not been previously described. The authors have therefore found it interesting to report a case fortuitously discovered in a patient with trigeminal neuralgia who underwent a fifth nerve microvascular decompression through the supracerebellar space. The angioma was not responsible for the neuralgia, but because of its potential risk of bleeding, the lesion was treated by resection of the trochlear nerve in its invaded portion. Then, the nerve was successfully repaired with an autograft harvested from the distal part of the sural nerve.

Anatomical landmarks of the Rhomboid fossa (floor of the 4th ventricle), its length and its width

Described are: 1. Length and width values of the rhomboid fossa. 2. Number and development of the transverse and oblique striae in the bottom area of the fourth ventricle. 3. The course of the facial nerve inside the pons and the medulla oblongata. 4. Some fiber tracts and nuclei in the tegmentum pontis and the medulla oblongata. 5. A very thick arcuato-cerebellar tract. 6. The results of our investigations are compared with descriptions of other researchers.

Left trochlear nerve palsy, unique symptom of an arachnoid cyst of the quadrigeminal plate. Case report

An arachnoid cyst of the quadrigeminal plate in a 49-year-old female is reported. This is the seventh published case of a cyst of this kind in an adult. The presenting symptom was an isolated left fourth cranial nerve palsy. Up to now, no other case with isolated superior oblique muscle palsy has been described which was caused by an arachnoidal cyst of the quadrigeminal plate.

Bilateral trochlear nerve paresis in hydrocephalus

Three patients with nonneoplastic hydrocephalus had bilateral paresis of the trochlear nerves. Associated signs, including paresis of upgaze, light-near dissociation of the pupils, and convergence-retraction nystagmus, suggested rostral involvement of the mesencephalon. Trochlear nerve paresis and accompanying signs improved after revision of ventricular shunts in two patients. Bilateral trochlear nerve paresis may be a localizing sign of involvement of the superior medullary velum (the anatomic site of trochlear nerve decussation) by a dilated sylvian aqueduct and/or downward pressure from an enlarged III ventricle.

Superior oblique myectomy and trochlectomy in recurrent superior oblique myokymia

In patients operated on for superior oblique myokymia with superior oblique tenotomy or tenectomy, symptoms of oscillopsia recur in approximately one-half. Failure of treatment may be caused by incomplete transection of the tendon or by residual attachments and postoperative adhesions between the proximal segment of superior oblique tendon and the globe which allow superior oblique muscle contractions to be partially transmitted to the globe. We report a patient with recurrent symptoms of superior oblique myokymia following superior oblique tenectomy who was successfully managed with superior oblique myectomy and trochlectomy via an anterior orbital approach.

Cystic schwannoma of the trochlear nerve mimicking a brain-stem tumor. Case report

A case is reported of a rare cystic schwannoma of the fourth cranial nerve which was interpreted as a probable intrinsic brain-stem lesion. The clinical approach to brain-stem tumors in terms of empirical treatment or surgical biopsy is discussed.

Trochlear neurinoma

A case of neurinoma of the trochlear nerve presenting with the sudden onset of headache followed by transient paresis of the right trochlear nerve in a 37-year-old woman is reported. Unique clinical manifestations of the tumor are discussed with a brief review of five cases reported in the literature.

[Experimental microsurgical exposure of cranial nerves III, IV and VI in the cat]

The operative techniques for experimental microsurgical studies on the third, fourth and sixth cranial nerves in the cat are described. We have found that the oculomotor nerve is best reached by a subtemporal approach. The trochlear nerve is easily exposed by a posterior temporal craniotomy while the abducens nerve should be approached through the clivus.

Return of function after intracranial suture of the trochlear nerve. Case report

An excellent functional result was obtained after microsuture of a trochlear nerve which was inadvertently divided during the course of a craniotomy. Successful intracranial suture of this nerve has not previously been reported. Ophthalmoscopic detection of excyclotorsion of the eye on the side of the trochlear nerve palsy is discussed, along with its value in the differential diagnosis of acquired vertical diplopia.

[Surgical treatment of eye muscle palsies (author's transl)]

The surgical treatment of an eye muscle palsy is indicated at the end stage of all possible conservative therapeutic measures. If after an interval of 8 to 12 months an eye muscle palsy manifests no change of pattern, the indication for surgical treatment is given, provided the pathologic process causing the palsy is no longer active. Of great importance for the evaluation of surgery are the forced duction test, measurement of saccadic velocity and electromyography. The aim of the surgical intervention is to eliminate diplopia and restore parallelism of the visual axes if possible with every line of vision, but above all with the largest possible visual field in the primary position and in downwards gaze. Any eye muscle palsy produces an overaction of the homolateral antagonist, an overfunction of the contralateral synergist and a secondary inhibition of the contralateral antagonist. Theoretically four surgical possibilities would result from these conditions. However, in practice the choice is reduced to weakening (recession, faden-operation) of the homolateral antagonist or the contralateral synergist or possibly both and to strengthening (resection, tucking) of the primary paretic muscle. Not infrequently, the surgical intervention has to be performed in different steps on different muscles of both eyes. In cases of total palsies muscles transposition or transplantation procedures (Hummelsheim-O'Connor, Jensen etc.) must be considered. A promising new method of restoring innervation to a paralyzed muscle is muscular neurotization (implantation of the inferior oblique muscle into the paralyzed denervated external rectus muscle in cases of abducens nerve paralysis).

[Indications for interventions on oblique muscles of the eye (author's transl)]

Interventions in cases of vertical squint are done in most cases on the oblique muscles. Vertical squint occurs most frequently as a vertical component in horizontal deviations in children with early concomitant strabismus. Without horizontal deviation but with binocular vision, it is rare in symmetric, but rather frequent in asymmetric forms: the sursoadductory form occurs as "congenital trochlear paresis", the deorsoadductory form as "Brown's syndrome". Acquired paresis can cause oblique vertical forms of squint. Operative indications to be observed: 1. Size and nature of vertical deviation, changes of field of gaze. In horizontal and vertical changes of gaze, different patterns of incomitance have to be observed. 2. Horizontal components of squint: Their correction does not abolish VD (vertical deviation), this should be performed by intervention on the obliqui. In A- and V- incomitance with dysfunction of the vertical motors, these have to be operated on. 3. Method of fixation: If forms of upper squint are asymmetric, both eyes should be operated on.

Evaluation of a surgical method for immobilizing the eye of an alert monkey

One eye of a macaque monkey was immobilized by severing the third, fourth, and sixth cranial nerves. The residual movements of the operated eye were measured by repeatedly mapping the position of a visual receptive field. Movements of several degrees were caused by contraction of the orbital musculature during the closure blink. The amount of movement was dramatically reduced by paralysis of the superficial orbital muscles with a local anesthetic. Side effects of surgical immobilization include increased risk of corneal clouding and eye infection. In one monkey intraocular pressure was lowered for several weeks. Regeneration of the severed nerves causes return of some voluntary movement of the eye, which is not coordinated with movements of the unoperated eye even after nine months postoperative survival. The suitability of this approach for studies on the visual nervous system is discussed.

Trochlear nerve sheath tumor; case report

✓ The author describes the presenting symptoms and treatment of a patient with a trochlear nerve sheath tumor.