pneumocephalus ( asymptomatic intracranial air ) is commonly seen in patients who have recently undergone craniotomy . 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 . a 40 kg , 15-year - old boy presented with a history of episodic headache , vomiting , and difficulty in walking of 4-years duration . 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 ] . he was premedicated with intramuscular glycopyrrolate 0.2 mg , one hour before induction of anaesthesia . in the operating room , 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 . 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 . 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 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 . 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 ) the incidence of pneumocephalus may vary from 57 - 73% in horizontal positions to 100% in sitting position . 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 . 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 . 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 , 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 . although the role of nitrous oxide in the genesis of tension pneumocephalus is controversial , 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 . postoperatively , the patients may present with delayed recovery , seizures , and arterial hypertension and reflex bradycardia ( cushing 's reflex ) due to mass effect . our patient made a slow uneventful recovery following twist drill - hole aspiration of air under water - seal . 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 . 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 . 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 .
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 .