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 Table of Contents  
CASE REPORT
Year : 2016  |  Volume : 5  |  Issue : 1  |  Page : 33-35

An unusual cause of trochlear nerve palsy and brainstem compression


Department of Neurosurgery, Grant Medical College and Sir JJ Group of Hospitals, Mumbai, Maharashtra, India

Date of Web Publication13-Jan-2016

Correspondence Address:
Jasmit Singh
Department of Neurosursgery, Grant Medical College and Sir JJ Group of Hospitals, Mumbai - 400 008, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2278-344X.173884

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  Abstract 

Schwannoma originates from the Schwann cells at the Obersteiner-Redlich zone, which marks the junction of central and peripheral myelin of the cranial nerves. Most frequently affected are the vestibular, trigeminal, and facial nerves followed by the lower cranial nerves. Trochlear schwannoma in the absence of neurofibromatosis is a rare entity. The purpose of this report is to serve as a reminder to consider trochlear nerve schwannoma in the list of differential diagnosis of such tumors as the outcome is far better than the intraaxial tumor in that location.

Keywords: Brainstem, palsy, schwannoma, trochlear nerve


How to cite this article:
Singh J, Kharosekar H, Velho V, Survashe P. An unusual cause of trochlear nerve palsy and brainstem compression. Int J Health Allied Sci 2016;5:33-5

How to cite this URL:
Singh J, Kharosekar H, Velho V, Survashe P. An unusual cause of trochlear nerve palsy and brainstem compression. Int J Health Allied Sci [serial online] 2016 [cited 2019 Sep 21];5:33-5. Available from: http://www.ijhas.in/text.asp?2016/5/1/33/173884


  Introduction Top


Neurinomas (schwannomas) originate from the Schwann cells at the Obersteiner-Redlich zone, which marks the junction of central and peripheral myelin of the cranial nerves. Most frequently affected are the vestibular, trigeminal, and facial nerves followed by the lower cranial nerves.[1],[2] Trochlear schwannomas in the absence of neurofibromatosis are a rare entity. Most of the patients present with trochlear nerve palsy. We report a rare case of trochlear nerve schwannoma who presented with hydrocephalus and signs of brainstem compression. The purpose of this report is to serve as a reminder to consider trochlear nerve schwannoma in the list of differential diagnosis of such tumors as the outcome is far better than the intraaxial tumor in that location.


  Case Report Top


A 35-year-old female presented to us with chief complaints of headache and imbalance while walking since 15 months. She also had complaints of diplopia, and her symptoms were progressive. Her higher mental functions were normal. She had left trochlear nerve palsy and fundus examination revealed bilateral papilledema. She also had left side grade III facial paresis with depressed gag reflex on the same side. Rest of the cranial nerve examination was normal. The patient had right-sided hemiparesis (4/5 MRC grade), plantars were extensor bilaterally. The patient was investigated with computed tomography (CT) brain and magnetic resonance imaging (MRI) brain with gadolinium contrast. CT brain with contrast revealed hypodense lesion on the dorsal aspect of the brainstem with contrast enhancement and hydrocephalus. MRI brain revealed contrast enhancing lesion on the dorsal aspect of the brainstem at the tentorial notch causing mass effect with hydrocephalus [Figure 1] and [Figure 2]. A diagnosis of the brainstem or tectal plate glioma was made, and a ventriculoperitoneal shunt was performed on an emergency basis. This relieved patient's headache and the patient was prepared for definitive surgery. A supracerebellar infratentorial approach was used in a semi-sitting position. Intraoperatively, tumor was identified as firm and gray-colored, which could be traced along the course of trochlear nerve. A plane of cleavage was present between the tumor and the brainstem. Intraoperative frozen report was suggestive of benign spindle cell tumor. Gross total resection was achieved. The patient was extubated at the end of procedure and remained neurologically intact. Over the period of time, her hemiparesis and brainstem compression signs improved, though trochlear nerve palsy persisted. Histopathology was suggestive of schwannoma. The patient was subsequently discharged and is following up regularly in our outpatient department [Figure 3], [Figure 4], [Figure 5].
Figure 1: Preoperative magnetic resonance imaging brain with contrast showing the lesion

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Figure 2: Preoperative magnetic resonance imaging brain with contrast showing the lesion

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Figure 3: Postoperative computed tomography brain with contrast showing complete excision of lesion with shunt in situ

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Figure 4: Magnetic resonance imaging brain with contrast at 1 year follow-up showing no residual lesion

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Figure 5: Magnetic resonance imaging brain with contrast at 1 year follow-up showing no residual lesion

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  Discussion Top


Cranial nerve schwannomas comprise 8–10% of all intracranial tumors, vestibular schwannoma being the most common. Nonvestibular cranial nerve schwannomas are uncommon. Of these, trigeminal schwannomas are the most common, but only account for up to 8% of intracranial schwannomas.[1],[2] Trochlear schwannomas are extremely rare; they arise mostly in middle-aged patients with an average age of 46 years, although they have been described in patients as young as 16 years old. They originate usually from the ambient part of the nerve and more rarely from its extradural cavernous part. They are classified as cisternal, cavernous, or cistern-cavernous.[1] Trochlear schwannomas may have a variety of presentations ranging from isolated trochlear nerve palsy to hemiparesis, cerebellar signs, or other cranial nerve deficits; depending upon the origin and extent of the tumor. Trochlear nerve palsy has only been seen in about half of the surgically confirmed trochlear schwannomas.[1] It has been proposed that due to the cisternal length of the fourth nerve, the tumor may displace and twist the nerve fibers instead of destroying them, which could account for the absence or late presentation of trochlear paralysis in these cases. As a general rule, resection of the trochlear schwannoma entails sacrificing the trochlear nerve, which results in a permanent fourth nerve palsy.[1] Preoperative diagnosis of this rare tumor is hardly made, but the possibility should always be considered; although with more widespread use of 3T MRI, the diagnosis of even small lesions is bound to increase. MRI brain with gadolinium contrast is the diagnostic modality of choice. Schwannomas have a characteristic MRI appearance. On T1-weighted images, they are usually iso- to hypointense compared to gray matter. On T2-weighted images, they are slightly hypointense to cerebrospinal fluid. Smaller schwannomas usually enhance homogeneously with gadolinium, but as they grow larger, they can become heterogeneous.[1] Often, trochlear schwannomas are observed along the cisternal portion of the nerve. Superior oblique atrophy may be noted.

As the entity is rare, there are no guidelines for the treatment. There are numerous reports in literature where small cisternal tumor is managed conservatively with serial MRI; reason being the fact that trochlear nerve is invariably sacrificed during surgery. It is not uncommon that patient is operated with some other diagnosis and TNS is diagnosed on histopathology. The subtemporal transtentorial approach with minor variations has been the most common approach used to resect these tumors.[1] Other approaches including pterional, suboccipital, the anterior transpetrosal approach, and presigmoid transpetrosal have been employed to resect trochlear nerve schwannoma.[1],[2] The ideal approach should be tailored based on the location and extent of the tumor. Overall prognosis in the absence of neurofibromatosis is good, also depends upon the preoperative neurological status.

Our patient had a large trochlear schwannoma, which was diagnosed only during surgery. The purpose of this report is to serve as a reminder to consider trochlear nerve schwannoma in the list of differential diagnosis of such tumors as the outcome is far better than other tumors in this location.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Elmalem VI, Younge BR, Biousse V, Leavitt JA, Moster ML, Warner J, et al. Clinical course and prognosis of trochlear nerve schwannomas. Ophthalmology 2009;116:2011-6.  Back to cited text no. 1
    
2.
Ho KL. Schwannoma of the trochlear nerve. Case report. J Neurosurg 1981;55:132-5.  Back to cited text no. 2
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]



 

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