Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 4, 2011, pp. 616-619

Neurology India, Vol. 59, No. 4, July-August, 2011, pp. 616-619

Case Report

Delayed otogenic pneumocephalus complicating ventriculoperitoneal shunt

Francesco Pieri¹, Carla Daniela Anania¹, Paolo Perrini¹, Michele Puglioli², Giuliano Francesco Parenti¹

¹ Department of Neurosurgery, University of Pisa, Pisa, Italy
² Neuroradiology Unit, Pisa, Italy
Correspondence Address: Paolo Perrini, Department of Neurosurgery, University of Pisa, Via Paradisa 2, 56100 Pisa, Italy, p.perrini@ao-pisa.toscana.it

Date of Submission: 23-Mar-2011
Date of Decision: 30-Mar-2011
Date of Acceptance: 31-Mar-2011

Code Number: ni11183

PMID: 21891946

DOI: 10.4103/0028-3886.84350

Abstract

Keywords: Pneumocephalus, Tegmen tympani defect, ventriculoperitoneal shunt

Introduction

Tension pneumocephalus can complicate severe head injury and neurosurgical interventions, ^[1] and rarely it has been described in association with paranasal sinus infection and skull-base tumors. ^[2],[3] Pneumocephalus following ventriculoperitoneal shunt is exceptionally rare and can occur when air is forced through the shunt ^[4] or enters the intracranial cavity through an osteodural defect of the paranasal sinuses or the pneumatized bone surrounding the middle ear. ^[2] We present a rare case of delayed occurrence of tension otogenic penumocephalus 1 year after placement of ventriculoperitoneal shunt.

Case Report

First admission: A 66-year-old man presented to our clinic with Hunt and Hess Grade 2 subarachnoid hemorrhage from a small anterior communicating artery aneurysm and hydrocephalus. He underwent urgent placement of an external ventricular drain (EVD) and endovascular aneurysm coiling. During hospitalization, he developed severe vasospasm and ischemic infarct in the left middle cerebral artery (MCA) territory despite aggressive therapy for vasospasm. He developed right hemiparesis and aphasia. Eventually, he failed EVD weaning and received a ventriculoperitoneal shunt. The shunt system included a programmable valve (Codman Hakim programmable valve system, Johnson & Johnson, Boston), whose pressure was adjusted to 120 mm H ₂ O. Postoperatively the patient improved neurologically and a repeat cranial computer tomography (CT) scan demonstrated resolution of hydrocephalus and was discharged to a rehabilitation facility on the tenth postoperative day. At 6-month follow-up, the patient was ambulating with a walker and had significant improvement of aphasia.

Second admission: One year after the first admission, the patient had clinical deterioration and was referred again to our department. On admission he had Glasgow Coma Scale score of 10 (E2, V3, M5) and was afebrile with no signs of meningism and rinorrhea. Routine laboratory parameters were normal. A CT scan obtained on admission revealed a massive intraventricular air collection and a porencephalic cyst in the right temporal lobe [Figure - 1]a and b. The shunt valve pressure was raised from 120 mm H ₂ O to 200 mm H ₂ O, and he was started on broad-spectrum antibiotics. A high-resolution CT scan with bone reconstructions obtained the following day confirmed a large pneumatocele on the petrous apex and revealed a right tegmen tympani defect [Figure - 2]a and b. He was taken-up for surgery, and a right subtemporal extradural approach provided exposure of the tegmen defect, which was covered by granulation tissue. The granulation was removed, and the bony defect was exposed. The tegmen tympani defect was sealed with temporalis fascia and fibrin glue. The postoperative course was uneventful and the clinical condition gradually improved in the following days. Serial postoperative CT scans demonstrated progressive resolution of pneumocephalus. He was discharged home 10 days after the operation with the valve-opening pressure at 120 mm H ₂ O. Six months postoperatively, he was ambulating with an assistance device and had minimal speech disturbances. Follow-up CT scans obtained at the last follow-up confirmed the complete resolution of pneumocephalus [Figure - 3]a and b.

Discussion

Otogenic shunt-associated pneumocephalus is a rare event, and only 13 additional cases have been reported [Table - 1]. ^{[3],[5],[6],[7],[8],[9]} A bony defect in the temporal bone and a pressure gradient between the defect and the intracranial space as the result of shunt were the common factors among the patients who developed otogenic shunt-associated pneumocephalus. The main predisposing factor is apparently a defect in the temporal bone surrounding the middle ear. Wide variations in the thickness of the tegmen tympani have been observed. The reported frequency of tegmen tympani defect was 21%, and more than five defects were observed in 6% of the specimen studied. ^[10] These observations suggest that the threshold for breaking the protective barrier between the intracranial cavity and the air cells surrounding the middle ear would likely be different among patients. Because of this interindividual variability, the mean time between shunt placement and development of tension pneumocephalus can be quite variable and the reported time interval ranged from 2 weeks to 30 months (mean, 9.7 months) [Table - 1]. Chronically increased intracranial pressure (aqueduct stenosis, communicating hydrocephalus) has been postulated to be an additional factor involved in the erosion of temporal bone. ^[11]

The low or negative pressure following shunt surgery may result in the fistula to be patent with resulting pneumocephalus. Postural changes of intracranial pressure after shunting have been well studied. ^{[12],[13],[14]} Patients with functioning shunts develop more negative ventricular pressures on assuming the upright position than do subjects without shunts. ^[12] In patients with shunts, the upright pressures are consistently negative, in the range of -15 to -35 cm H ₂ O. ^[12] The occurrence of otogenic pneumocephalus in patients with shunts may be explained by the "ball valve" mechanism initially described by Dandy. ^[15] In the presence of rapid linear fall in intraventricular pressure associated with the upright position, air may enter the intracranial space through the fistulous connection. When the pressure differential from atmosphere to intracranial space is reduced, the brain tissue seals off temporarily the dural and bone defects. This mechanism prevents egress of the entrained air and loss of cerebrospinal fluid (CSF) through the fistula. In this scenario, further CSF drainage promotes the entry of air by releasing the brain plug and it may induce progressive neurological deterioration. When the brain tissue is tightly adherent to the breached dura at the fistula site, air may flow directly into the brain parenchyma, setting up a tension pneumatocele. In patients with otogenic pneumocephalus, the occurrence of a pressurized porencephalic cyst in the temporal lobe is a common event, and it was found to occur in 64% of published cases. ^{[3],[5],[7],[9],[16]} The presence of a porencephalic cyst is generally a good indicator of the fistulous connection. High resolution CT-scan using a bone algorithm is an appropriate tool to locate the presence of bone defect in the skull base. In our patient, coronal CT scan clearly demonstrated the tegmen tympani defect and the communication of the temporal pneumatocele with the middle ear.

Effective management of otogenic pneumocephalus depends on a careful identification of skull base defect. Temporary closure of the shunt may stop the vicious circle established among displaced volume of CSF, intracranial negative pressure, and pneumocephalus. ^[7],[8] Two of the 14 reported cases were treated successfully by shunt manipulation alone. ^[7],[8] It is worth noting that in one of these cases ^[7] temporary CSF leakage from the mastoid air cells occurred after shunt ligation. The subtemporal extradural approach is a simple and highly effective way to repair the tegmen tympani defect. ^{[3],[5],[9],[11],[16]} Sealing the defect through a transmastoid approach can successfully treat patients with defect of the posterior mastoid plate and posterior fossa pneumatocele. ^{[6],[17],[18]}

References

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