Pneumocephalus is the presence of air or gas within the cranial cavity. It is usually associated with disruption of the skull: after head and facial trauma, tumors of the skull base, after neurosurgery or otorhinolaryngology, and rarely, spontaneously. The dry tap can lead to multiple attempts for ventriculostomy with added risk of complications. It can add dilemma as to what the subsequent management would be.There is also increased risk of tension pneumocephalus, seizures and shunt failure due to blockage by air bubbles. Head down positioning, adequate cruciate dural incision prior to cortex puncture and avoiding excessive egress of CSF are certain nuainces that will help to prevent such complication during the procedure.
According to a case reported by Sunil Munakomi, a 35 year old male from Nepal had undergone External Ventricular Drainage (EVD) placement for the management of post traumatic hydrocephalus. He had undergone craniotomy and evacuation of acute subdural hematoma following road traffic accident. Later as he was dependent on EVD, he was planned for VP shunting. Intraoperatively, there was dry tap during an attempt of ventriculostomy from the Kocher’s point. The proximal shunt was placed in assumed position of frontal horn of lateral ventricle. The patient was managed with 100% oxygen and stringent neurological monitoring for evaluating early neurological deterioration. After complete resolution of the condition, repeat computerized tomography scan showed that the proximal shunt was in third ventricle.
Pneumocephalus usually occurs after head trauma, skull base fractures and asociated CSF fistulas. If there is a valve mechanism which allows air to enter the skull but prevents it from escaping, a tension pneumocephalus can occur (similar to what can happen in a tension pneumothorax). CT scans of patients with a tension pneumocephalus typically show air that compresses the frontal lobes of the brain, which results in a tented appearance of the brain in the skull known as the Mount Fuji sign. Pneumocephalus has also been shown to follow neurosurgical procedures such as deep brain stimulation, where while seemingly innocuous to the patient, may cause brain shift and subsequent stereotactic inaccuracy. Efforts are made by neurosurgeons to reduce pneumocephalus volume during surgery, and thus, subsequent brain shift. The duration of the shunt surgery must be as short as possible and CSF leakage during the connection of the shunt system must be avoided. Another factor can be during puncturing of the cortex. Adequate cruciate incision must be given to prevent the passage of environmental air into the subdural space. Filling of the subdural space on the ventriculostomy site with the irrigation fluid until overflowing might be helpful in the outflow of the air from the intracranial vault and reducing the risk of this rare complication. Cortical atrophy probably had also an effect on the isolated air collection within the subdural space. Another remote possibility in our case would be any leak in the closed drainage system of the previous EVD drain. Proper layered closure of the skin in VP shunt surgery is the most important factor for prevention of this rare complication.
The dry tap can lead to multiple attempts for the correct trajectory thereby increasing the risk of false trajectories and also track hematomas. If there is no EVD hen it would lead to termination of the procedure thereby adding the morbidity and risk of subsequent surgery for the same. There is also risk of seizures and rapid neurological deterioration. Once it occurs, close monitoring of the patient, rapid identification of tension pneumocephalus and immediate surgical intervention is life-saving.