Recurrent Pneumocephalus due to over Draining Thecoperitoneal Shunt in a Patient with Multiple Skull base Defects

Abstract

We report a case of recurrence pneumocephalus in a 42-year-old man who underwent transnasal CSF leak repair for left lateral sphenoid meningocele, with thecoperitoneal(TP) shunt. The pneumocephalus was attributed to negative intracranial pressure created by an over draining shunt in the presence of multiple skull base defects.

Introduction

Pneumocephalus and pneumoventricle are known to occur following trauma, iatrogenic and nontraumatic causes [1]. Large amounts of intracranial accumulation of air over time (with in subdural space or ventricles), exerting mass effect by increasing the intracranial pressure (ICP) is known as tension pneumocephalus or pneumoventricle [2]. This results in altered consciousness, coma or even death when left untreated [3]. We report a case of recurrent pneumocephalus along with pneumoventricle in a patient with skull base defects presenting with cerebrospinal fluid (CSF) rhinorrhea, who underwent transnasal endoscopic repair of skull base defects followed by a theco-peritoneal (TP) shunt insertion for idiopathic intracranial hypertension (IIH).

Case Report

A 42-year-old male patient presented with a 3 days history of CSF rhinorrhea from the left nostril. There was no history of trauma or prior surgery. CT and MRI of brain were performed which showed a 3 mm bony defect in the left middle cranial fossa (MCF) with a meningocele filling the lateral recess of the left sphenoid sinus (Fig. 1a, b & e). Another 3 mm bony defect was detected in the right tegmen tympani (Fig. 1d & h). Other imaging findings including intraosseous cephaloceles (Fig. 1b, f, g, c) in the right lateral sphenoid were suggestive of IIH with CSF leak from the left MCF defect secondary to IIH.

Fig. 1.

Idiopathic intracranial hypertension. MRI Brain Coronal T2 DRIVE (a) & (b) and Coronal HRCT (e) & (f) shows hyperpneumatization of the sphenoid sinus with a small bony defect in the floor of the left MCF (red arrow) with a large meningocele filling the hyperpneumatised lateral recess of the sphenoid sinus (blue arrow). Fluid in the rest of the left sphenoid sinus. No gliosis in the adjacent brain. Small intraosseous cephaloceles in the right lateral sphenoid with thinning of the overlying bone (yellow arrow). No extension into the sphenoid sinus or fluid within the right lateral recesses or sphenoid sinus. Sagittal T2 (c) shows partial empty sella (dark green arrow) with reduced vertical height of the gland measuring 3 mm and normal mamillopontine distance of 6.8 mm. MR venogram (g) shows hypoplastic left transverse sinus with stenosis of bilateral transverse sinus (light green arrow). HRCT temporal bone coronal (d) & sagittal (h) shows small bony defect in the right tegmen tympani (orange arrow) with middle ear and mastoid effusion (dark blue arrow)

The patient subsequently underwent transnasal endoscopic repair, where the defect in the left MCF with active leak was identified and sealed off. In view of high CSF opening pressure (> 25 cm H2O) a TP shunt was inserted. Postoperatively, the patient was asymptomatic. Two months later, the patient presented with gait imbalance and decreased sensorium. CT brain performed now showed pneumocephalus in subarachnoid space with dilated ventricles, penumoventricle and diffuse cerebral oedema (Fig. 2 c & d). Now a focal breach along the medial wall of the intraosseous cephaloceles in the right lateral sphenoid was identified [which was intact on the previous scan (Fig. 1b & f)] with adjacent air loculi (Fig. 2a & b). The patient underwent emergency aspiration of pneumoventricle with right External ventricular drainage (EVD) placement and transnasal endoscopic repair of the defect in the right lateral sphenoid. TP shunt revision was also performed. Good resolution of pneumocephalus was noted on the post operative imaging (Fig. 2e & f). Six months later, the patient presented again with diffuse headache and hissing noise in the right ear. There was recurrence of pneumocephalus along the right cerebral convexity with thin subdural effusion along bilateral convexities (Fig. 3b, c & d). Pocket of intracranial air was noted adjacent to the right mastoid, close to the bony defect seen in the tegmen tympani on the first scan (Fig. 3e & f). There was also evidence of distended right transverse sinus (Fig. 3b) with near complete disappearance of right transverse sinus stenosis seen on prior imaging (Fig. 1g). An increase in the vertical height of pituitary gland was also noted as compared to the prior study – 3 mm in the first scan (Fig. 1c)  and 6 mm in the third visit (Fig. 3h). Mamillopontine distance was also found to be decreased during the third visit (0.58 mm). These imaging findings were consistent with intracranial hypotension secondary to CSF overdrainage by the TP shunt and resultant pneumocephalus, possibly through the bony defect in the right tegmen tympani. The patient underwent TP shunt blockage. His complaints resolved postoperatively and remained asymptomatic until the last follow-up.

Fig. 2.

Tension pneumocephalus and post EVD. Coronal CT brain window (a) and bone window (b) shows breach in the medial wall of the right intraosseous cephaloceles (yellow arrow) (seen intact on the previous scan Fig. 1b & f) in the right lateral sphenoid with air loculi at the site of breach and hypodensity in the adjacent temporal lobe (cerebritis). CT Brain axial images (c) shows extensive pneumocephalus in the subarachnoid space and ventricles with dilatation of the lateral ventricles and effacement of the sulci in bilateral cerebral hemispheres. CT Brain axial images (d) performed after few hours of Fig. 2c shows progressive increase in the ventricular dilatation and sulcal effacement. CT Brain axial images (e) and (f) performed few weeks after the second surgery shows significant interval resolution of the pneumocephalus, hydrocephalus and sulcal effacement as compared to the Fig. 2d. Persistent hypodensity in the right temporal lobe

Fig. 3.

Recurrent pneumocephalus. MRI Brain axial FLAIR (a), FLAIR (b) & (c), SWI (d), T2 (f) and coronal T2 (e) & (g) performed few months after the second surgery shows pneumocephalus along the right cerebral convexity. Gliosis in the right temporal lobe (b) & (g) with distended right transverse sinus (orange arrow). Air is noted adjacent to the right tegmen tympani (red arrow) close to region of the tegmen tympani defect seen in Fig. 1d & h. Subdural effusion along bilateral convexity and petrous ridge. Mixed signal intensity with in the sphenoid sinus and lateral recesses (yellow arrow) related to post operative changes from CSF leak repair. MR Venogram (i) No venous stenosis, resolved compared to earlier MR venogram (Fig. 1f). Sagittal T1 (h) Partial empty sella (dark green arrow) with increase in the vertical height of the pituitary gland (6 mm) and decrease in mamillopontine distance (5.8 mm) as compared to the prior image (Fig. 1c)

Discussion

The presence of air in the intracranial space and in the ventricles are termed as pneumocephalus and pneumoventricle, respectively [4]. When the air is under high pressure, it is referred to as tension pneumocephalus [1, 2]. The most common cause of pneumocephalus is head trauma, followed by surgeries [5]. Post-operative pneumocephalus occurs due to inadequate repair of the defects in the skull base which were opened during surgery or due to skin fistulas just above the burr hole. Congenital skull base defects, are another cause with congenital tegmen tympani defects seen in about 20% of general population [6]. The common symptoms of pneumocephalus include headache and altered mental status [4, 7], severity of which depends on the amount of intracranial air.

Two mechanisms have been proposed for the development of pneumocephalus:

• The ‘Dandy’s ball-valve effect’ occurs when elevated upper airway pressures, drive air intracranially in one direction through a preexisting defect, elevating the ICP. The defect is further tamponaded by the brain or meninges, which prevent the exit of air and trap the air in the intracranial space [1, 5, 8, 9].

• The ‘Horowitz inverted soda bottle effect’ occurs when negative intracranial pressure caused by a loss of CSF, such as via a lumbar drain or TP shunt, allows air to flow from the extra to the intracranial space across the pressure gradient through a defect in the skull base [1, 5, 8, 9].

Our patient had a spontaneous CSF rhinorrhea attributed to IIH. A sustained increase in ICP (due to IIH) causes erosions creating osteo-dural defects in pneumatized parts of the skull base which are plugged by the meninges or brain [1, 10]. These defects are the sites of CSF leaks leading to CSF rhinorrhea. When CSF diversion procedures are performed, due to a drop in ICP, these erosion points open with the inward flow of air, resulting in pneumocephalus [1]. This air is further prevented from escaping by the resealing of the defects, and this cycle repeats, resulting in tension pneumocephalus. In our case, a sustained negative pressure was caused by the TP shunt, as evident by the imaging features of intracranial hypotension (Fig. 3) with resultant recurrent pneumocephalus along with pneumoventricle. The patient also had features of tension pneumocephalus (dilated lateral ventricles and effacement of bilateral cerebral sulci) in his second visit. Here, both ‘inverted soda bottle effect’ and the ‘ball valve effect’ must have led to recurrent pneumocephalus. The treatment of tension pneumocephalus secondary to excessive CSF drainage includes interruption of the inverted soda bottle mechanism, which in our case meant clamping the TP shunt. An EVD was also placed to create an exit route for the intraventricular air. This case highlights the complex interaction between pressure dynamics, anatomical features, and CSF drainage procedures, underscoring the need for heightened awareness of tension pneumocephalus and its potential recurrence in patients with skull base defects undergoing CSF diversion procedures.

Funding

No funding was received to assist with the preparation of this manuscript.

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Nothing to be declared. The authors have no relevant financial or non-financial interests to disclose.

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Competing Interests

The authors have no competing interests to declare that are relevant to the content of this article.