Neurology India, Vol. 58, No. 2, March-April, 2010, pp. 327-328
Letter To Editor
Posterior fossa arachnoid cyst presenting with cerebrospinal fluid rhinorrhea
Alok A Umredkar1, Sunil K Gupta1, Sandeep Mohindra1, Parmjeet Singh2
1 Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India
Correspondence Address:Alok A Umredkar, Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India, email@example.com
Date of Acceptance: 02-Jul-2009
Code Number: ni10087
Arachnoid cyst (AC) involving the posterior fossa may be asymptomatic  or may produce a wide variety of posterior fossa symptoms with little specificity.  Posterior fossa AC with isolated cerebrospinal fluid (CSF) rhinorrhea as a presenting symptom has not been reported in the literature.
An 18-year-old girl presented with complaints of watery nasal discharge spontaneously of one week duration. Her computed tomography (CT) scan of brain showed posterior fossa cystic lesion with obstructive hydrocephalus [Figure - 1]a. Magnetic resonance imaging (MRI) scan showed normal cerebellar hemispheres, with posteriorly placed midline cystic lesion compressing the fourth ventricle, without any communication with the fourth ventricle, ruling out Dandy Walker malformation. Thinking the primary cause of CSF rhinorrhea as hydrocephalus due to posterior fossa arachnoid cyst, she underwent posterior fossa surgery, sub occipital craniotomy and de-roofing of AC. Postoperatively, her CSF rhinorrhea subsided for a few days only. Repeat CT scan showed persistent hydrocephalus. She underwent right ventriculo-peritoneal shunting. Her CSF rhinorrhea subsided completely and she was discharged after two weeks. After one month she was again admitted with complaints of intermittent CSF rhinorrhea. Her CT scan showed pneumocephalus with normal size ventricles with shunt in situ [Figure - 1]b. MR cisternography showed evidence of CSF leak at the cribriform plate [Figure - 1]c. She underwent endoscopic sinus surgery for repair of CSF leak twice. At first, the ENT surgeons could not find the leak site. In the second attempt, they defined the leak site in the region of the cribriform plate and repaired it. Postoperatively, the patient was fine and was discharged after one week. After one month patient presented to the emergency with altered sensorium and vomiting. CT scan brain showed increased pneumocephalus in frontal region and pneumoventricle with mass effect (tension pneumocephalus) suggesting failure of endoscopic repair [Figure - 1]d. Bifrontal craniotomy and anterior cranial fossa repair with pericranial grafting, both intra and extradural was done. Postoperatively; patient was conscious, alert with no CSF leak. She was discharged after one week. At six-month follow-up she was fine and her CT showed disappearance of pneumocephalus and pneumoventricle.
Common sites of AC include the middle fossa and the posterior fossa, especially the cerebellopontine angle (CPA). ,, AC involving the posterior fossa may be asymptomatic or may produce a wide variety of posterior fossa symptoms with little specificity such as ataxia, dizziness, tinnitus, hearing loss,  hysterical breathlessness, postural headache,  seizures and tremors.  Posterior fossa AC presenting with isolated CSF rhinorrhea without any clinical features suggestive of posterior fossa lesion or of raised intracranial pressure (ICP) is rare.
Management options include serial cyst fenestration, stereotactic puncture, endoscopic cyst fenestration, cystoperitoneal shunt, cyst marsupialization into the subarachnoid space, and complete or partial resection of the cyst wall. In many cases, AC are asymptomatic and do not grow progressively. Conservative management with regular radiological control will identify those cases with gradual cyst enlargement that need surgical treatment. In cases of posterior fossa communicating AC with associated hydrocephalus, ventriculoperitoneal shunting should first be attempted. If no relief of the preoperative symptoms is achieved and serial postoperative scans demonstrate no shrinking of the cyst, open surgery should be performed. 
Spontaneous CSF rhinorrhea is an uncommon condition. All patients with spontaneous CSF rhinorrhea, irrespective of the cause, require surgery to treat the responsible lesion and to close the dural defect at the site of its communication with the air sinuses/nasal cavity. The treatment of hydrocephalus or a tumor removal takes precedence over any attempt to close the fistula as the initial operation. Many a times, attending to the cause responsible for raised ICP is enough to stop the leak. , In the present case, the patient probably had erosion of the bony floor of the anterior cranial fossa due to longstanding persistent chronic pressure secondary to hydrocephalus. Reduction of ICP by de-roofing the cyst and by a ventriculoperitoneal shunt probably created a low pressure in the intracranial compartment causing sucking of air in the cranium leading to tension pneumocephalus. It is our opinion that in such situations, repair of the bony defect (ACF) should be performed simultaneous to the cyst decompression/shunting procedure.
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