Tension pneumoventricle after excision of third ventricular tumor in sitting position.

Occurrence of tension pneumoventricle (symptomatic intraventricular air) can result in rapid clinical deterioration in an otherwise stable patient. It is a rare clinical entity, mentioned in relation to cerebrospinal fluid (CSF) diversion procedures, during the late postoperative period. We present a patient with posterior third ventricular tumor who underwent excision by midline suboccipital craniotomy in sitting position. Neurological status of the patient deteriorated rapidly in the immediate postoperative period owing to development of tension pneumoventricle. The condition improved after twist-drill burr-hole evacuation of air under water-seal. Pre-existing gross hydrocephalus, exploration of third ventricle in sitting position, and residual tumor in third ventricle were possibly the factors responsible for this complication.

Introduction

Pneumocephalus (asymptomatic intracranial air) is commonly seen in patients who have recently undergone craniotomy.[1] It may occur in epidural, subdural, intraparenchymal or intraventricular regions. Intraventricular pneumocephalus, also known as pneumoventricle, is a rare clinical entity. It has been reported primarily following cerebrospinal fluid (CSF) diversion procedures.[2] Small amounts of air in ventricle is asymptomatic and do not require any active intervention. However, the presence of tension pneumoventricle (symptomatic intraventricular air) may lead to significant clinical deterioration. We present a case of extensive pneumoventricle after excision of third ventricular tumor.

Case Report

A 40 kg, 15-year-old boy presented with a history of episodic headache, vomiting, and difficulty in walking of 4-years duration. There was no history of trauma or medical comorbidities. His neurological examination revealed bilateral upward gaze palsy with alternate convergent squint. The patient had positive cerebellar signs in the left side. Computed tomographic (CT) scan of head showed a posterior third ventricular mass involving adjacent left thalamus causing proximal hydrocephalus of lateral ventricles and anterior third ventricle [Figure 1a]. A midline suboccipital craniotomy and excision of the tumor in sitting position was planned. The routine investigations were within normal limits. He was premedicated with intramuscular glycopyrrolate 0.2 mg, one hour before induction of anaesthesia. In the operating room, routine monitors like ECG, pulse oximetry, and noninvasive BP were connected. Anesthesia was induced with intravenous propofol 100 mg and fentanyl 100 mg, followed by rocuronium 40 mg to facilitate tracheal intubation. Anesthesia was maintained with isoflurane, 66% N2O in O2, and intermittent boluses of fentanyl and rocuronium. Arterial BP, central venous pressure (CVP), and nasopharyngeal temperature were monitored, continuously, during the intraoperative period. End-tidal CO2 and CVP were maintained at 35 ± 2 mmHg and 8 ± 2 mmHg, respectively. The surgery lasted for 5 hrs. Blood loss of 350 ml was recorded. Fluids were adequately replaced and the patient remained hemodynamically stable throughout the procedure. At the end of surgery, residual neuromuscular blockade was reversed but the trachea was not extubated since the patient remained drowsy. He was transferred to intensive care unit but drowsiness remained even an hour later. Gradually the patient became unconscious (able only to localize pain). An urgent CT scan of head was done which revealed extensive pneumoventricle and a small residual tumor in left lateral ventricle [Figure 1b]. Under local anesthesia, right frontal precoronal twist drill burr-hole was made and around 50 ml of air was tapped under water seal. The patient became conscious but drowsiness persisted. A repeat CT scan 12 hrs later revealed decreased extent of ventricular air. Ventricular tapping was repeated and approximately 30 ml of air was aspirated. The patient was mechanically ventilated for yet another day and trachea was extubated on third postoperative day (POD). The patient made a gradual recovery and was discharged from the hospital on eighth POD.

Figure 1

Computed tomographic scan of head showing posterior third ventricular mass involving adjacent left thalamus causing proximal hydrocephalus of lateral ventricles and anterior third ventricle (a); and postoperative extensive pneumoventricle involving both lateral ventricles and a small residual tumor in left lateral ventricle (b)

Discussion

There is always some degree of intracranial air entrainment after craniotomies. The incidence of pneumocephalus may vary from 57-73% in horizontal positions to 100% in sitting position.[3] Sitting position promotes the development of pneumocephalus through an ‘inverted pop bottle’ mechanism.[4] As CSF flows out of the skull, a negative pressure is created within the intracranial space. This negative pressure does not allow efflux of more CSF until air enters to take its place and equilibrates the pressure differential. Tension pneumocephalus develops when the volume of sealed intracranial air increases either by expansion of gas on warming to body temperature or by further diffusion of gas into the space.[5] Other etiological factors implicated include nitrous oxide anesthesia, prolonged surgery, gross hydrocephalus, functional ventriculoperitoneal (VP) shunt in situ, intraoperative administration of mannitol or frusemide, sitting position, and head-up position after surgery.[36]

Unlike supratentorial pneumocephalus, occurrence of tension pneumoventricle is rare. Most of the reported cases of tension pneumoventricle developed after CSF shunting procedures for hydrocephalus. This patient developed tension pneumoventricle after being operated for a posterior third ventricular tumor in the sitting position without a functioning VP shunt in situ. Prophylactic placement of an external ventricular drainage (EVD) during intraoperative period could have avoided this complication. However, EVD placement is associated with a risk of infection. The development of pneumoventricle in this case appears to be multifactorial. However, the main contributing factors seem to be large amount of CSF loss during exploration of third ventricle in addition to sitting position and pre-existing hydrocephalus. Theoretically, the influx of air into the intracranial cavity is greater in the presence of a noncompliant ventricular system because the ventricles do not collapse as the fluid is drained out and more air is allowed to fill the ventricle.[7] Although the role of nitrous oxide in the genesis of tension pneumocephalus is controversial,[8] it is wise to avoid its use in patients undergoing a repeat craniotomy within 2-3 weeks. In this case, the factors that lead to symptomatic (tension) pneumoventricle appears to be the presence air, residual tumor and blood in the third and fourth ventricles, thereby, causing features of obstructive hydrocephalus.

Tension pneumoventricle may manifest as deterioration of consciousness with or without lateralizing signs, severe restlessness, generalized convulsions, or focal neurologic deficits.[9] Postoperatively, the patients may present with delayed recovery, seizures, and arterial hypertension and reflex bradycardia (Cushing's reflex) due to mass effect. Prompt diagnosis requires a high index of suspicion after craniotomy. An urgent CT scan can identify intracranial air as small as 0.5 ml. Our patient made a slow uneventful recovery following twist drill-hole aspiration of air under water-seal.

Perrin and colleagues[7] suggested replacement of air in the ventricles with warm irrigation fluid. They suggest that the fluid would be less toxic than air and more likely to flow down the shunt. A slow infusion of normal saline through a subarachnoid catheter in the frontoparietal region during the surgical procedure may prevent the entrainment of air.[10]

A similar case of tension pneumoventricle has been reported in a patient who underwent excision of midbrain tectal plate tumour via a midline suboccipital approach while in sitting position.[11] The patient developed rapid neurological deterioration in the immediate postoperative period. Insertion of an external ventricular drain resulted in prompt recovery.

Conclusions

The present case highlights a rare complication of craniotomy performed in the sitting position. Breach of third ventricle, in presence of other contributing factors, resulted in massive loss of CSF which possibly led to accumulation of air in the ventricles. Close postoperative monitoring and an urgent CT scan helps in rapid diagnosis and successful management of the condition.