LETTER TO THE EDITOR

Bilateral abducent nerve palsy as the initial clinicalmanifestation of medulloblastoma

Sachin Baldawa & C. V. Gopalakrishnan

Received: 10 July 2010 /Accepted: 12 July 2010 /Published online: 21 July 2010# Springer-Verlag 2010

Sir,A 6-year-old girl was brought to the neurosurgical departmentas her mother had noticed inward deviation of the left eye of 4-week duration followed by inward deviation of the right eyeafter 2 weeks. She did not have any clinical featuressuggestive of raised intracranial pressure. Fundus examinationwas normal. Cranial nerve examination demonstrated bilateralabducent nerve palsy. Rest of the neurological examinationwas normal. Magnetic resonance imaging brain revealed a 3×2 cm lesion in the inferior vermis, hypointense on T1-weighted image, hyperintense on T2-weighted and FLAIRimages. It showed restriction on diffusion-weighted imagingand heterogenous enhancement on gadolinium administra-tion. There was no evidence to suggest presence of leptome-ningeal metastasis. Imaging features were suggestive ofmedulloblastoma. Spinal screening revealed the presence ofintrathecal drop metastasis at L5-S1 vertebral level. The childwas taken up for tumor resection. Midline suboccipitalcraniectomy was performed and the tumor was radicallydecompressed. Cerebrospinal fluid (CSF) cytology showedthe presence of malignant cells. Post-operatively, she hadbilateral sixth nerve palsy that persisted at follow-up. Thepatient was started on adjuvant cranio-spinal radiotherapy.

Presence of sixth nerve palsy, especially if bilateral, is oftenconsidered as a false localizing sign. Abducent nerve palsycommonly occurs following raised intracranial pressure eitherdue to supratentorial tumors or infratentorial tumors withobstructive hydrocephalus. The resultant central herniationleads to axial displacement of the brainstem. The sixth nerve

with its long intracranial course is highly sensitive to stretch.Downward displacement of the brainstem causes distortion ofthe abducent nerve or its compression against the petrosphe-noid ligament in the Dorellos canal or against the ridge ofpetrous temporal bone [3]. Dysfunction of the axoplasmicflow is often said to be responsible for this reversible palsy[2]. This false localizing sign diverts attention from theprimary pathology that may remain clinically silent.

Sixth nerve palsy can also rarely occur as a falselocalizing sign in posterior fossa abnormalities in absenceof obstructive hydrocephalus and raised intracranialpressure. This false localizing sign has been reportedfollowing posterior fossa extradural hematoma occurringpostoperatively [2]. This is probably due to the forwarddisplacement of the brainstem, rather than downwardsresulting in distortion of the nerves in its intracranialcourse. Bilateral abducens nerve palsy occuring in Chiari1 malformation is due to the downward traction of theponto-medullary junction [4]. Foramen magnum decom-pression relieves the traction on the nerve. Seeding ofprimary brain tumors into the subarachnoid space is wellknown phenomenon in medulloblastoma. However, theinitial signs and symptoms in primary brain tumors areseldom due to diffuse leptomeningeal metastasis. Metas-tasis at a distinct site can present with misleading clinicalsymptoms especially if the primary tumor is occult. Extentof CSF seedling does not depend on the primary tumorsize [1].

In our case, the presence of malignant cells on CSFcytology and lumbosacral drop metastasis on imagingfavored leptomeningeal metastasis as the most probablecause for bilateral sixth nerve palsy as the initial presentingsign even though it was not evident on advanced imaging.Thus, the presence of posterior fossa tumor needs to beconsidered as one of the differential diagnosis in a patient

S. Baldawa : C. V. Gopalakrishnan (*)Department of Neurosurgery, Sree Chitra Tirunal Institute forMedical Sciences and Technology,Trivandrum 695011, Indiae-mail: drgopal@sctimst.ac.in

Acta Neurochir (2010) 152:1947–1948DOI 10.1007/s00701-010-0751-1

presenting with bilateral sixth nerve palsy in the absence ofraised intracranial pressure.

References

1. Corbett JJ, Newman NM (1981) Symptomatic leptomeningealmetastasis preceding other manifestations of occult primary braintumors. Surg Neurol 15(5):362–367

2. Johnston NJ, Choudhari KA (2003) Bilateral sixth nerve palsy: arare presentation of postoperative posterior fossa extraduralhaematoma. Br J Neurosurg 17(3):272–273

3. Larner AJ (2003) False localising signs. J Neurol NeurosurgPsychiatry 74:415–418

4. Miki T, Ito H, Kawai H, Nakanishi T (1999) Chiarimalformation (type 1) associated with bilateral abducensnerve palsy; case report. No Shinmkei Geka 27:1037–1042

1948 Acta Neurochir (2010) 152:1947–1948