tension pneumocephalus is infrequent and the limited number of cases reported all involve positive airway pressure ventilation after head trauma with an undiagnosed skull fracture . we present a rare case of violent pneumocephalus after head trauma not involving mask ventilation but based on pathological respiration pattern , kussmaul breathing . a 53 year old man , known with insulin dependant diabetes mellitus , sustained a heavy blunt trauma to the back of the head from a crane arm . he was found estimated 15  h after the incident and was transported to the nearest hospital without intubation . on admission to the local trauma centre his glasgow coma score ( gcs ) was eight ( eyes two , motor five , verbal one ) . there was bleeding from the external meatus of the right ear and a periorbital haematoma on the right side . initial blood gas results showed plasma glucose 36  mmol / l , ph 7.3 , plasma lactate 5.8  mmol / l , base excess 8.3  mmol / l . there was diminished skin turgor and a strong smell of acetone emanating from the patient . 1 ) revealed multiple skull base fractures through the clivus , the petrus bone to the foramen magnum and through the frontal sinus and the sphenoid sinus and massive tension pneumencephalon ( tp ) bi - frontally compressing the cerebrum to about 2/3 of the cranial volume ( figs . 1 and 2 ) the neurosurgeon conferred advised making a burr hole in the right temporal region to relieve the pressure pneumo - encephalon before transport to the neurosurgical department . the burr hole was performed and air bubbled out of the incised dura . upon arrival at the neurosurgical department the patient underwent another ct - scan showing sustained pneumocephalus with compression on the brain bifrontally and air compressing the brainstem . furthermore an acute subdural haematoma was noted located under the burr hole . the patient was at that point sedated to gcs three , intubated , non - responsive and had normal - responsive pupils . the pt . underwent acute operation ; making use of the fracture lines in the skull and the subdural haematomas was evacuated . the brain that had been exposed to air for 20  h had a yellowish and dry surface and was hyperaemic . finally an intracranial pressure ( icp ) monitor was inserted through a small twist drill hole into the parenchym pre - coronally on the opposite site . post - operative ct showed reduction of the intracranial air and a normal calibrated brain with normal surface contours and parenchyma ( fig . the patient was admitted to neurointensive care unit , under surveillance with contiguous icp monitoring . two weeks later the patient was still intubated due to pulmonary causes , gcs ten ( eyes three , motor six , verbal one ) and with no obvious focal neurological deficits and was referred to a neurorehabilitation centre . two years later , the patient is awake , has gcs 15 and no cognitive deficits . when the bicarbonate ions buffering capacity is used , plasma ph and bicarbonate decline and respiration is stimulated . coma is uncommon ; most patients are lucid or exhibit mild - to - moderate disturbance of consciousness . we believe that the rapid and shallow respiration in this case has pushed the air intracranial , has caused the increasing pressure to the brain and the result is pneumocephalon . pneumocephalus develops due to a cranial or facial fracture through which air enters the intracranial cavity . tp is characterized by continued build - up of air within the cranial cavity , due to valve - effect usually in relation to a skull base fracture . head position during cranial surgery , duration of surgery , nitrous oxide ( n2o ) anaesthesia , intraoperative osmotherapy , hyperventilation , spinal anaesthesia , barotrauma , continuous csf drainage via lumbar drain , epidural anaesthesia are suggested as surgical causes . meningitis , otitis media , orbital emphysema and high pressure air applied into the orbit is also suggested as reasons to pneumocephalus without bone fracture . although the condition is generally asymptomatic , pneumocephalus of sufficient volume is implicated in postoperative lethargy , headaches , confusion , hemiparesis , abducens nerve palsy , mental changes and even seizure , in which cases treatment may be necessary . 1 . the pathophysiologic process starts with cerebral spinal fluid leak in the presence of associated discontinuity of the cranium and leptomeningeal disruption . subsequent development of relative negative intracranial pressure results in a sufficient  vacuum effect  to cause additional accumulation of air within the cranial cavity . at the site of the leptomeningeal tear , the positive end tympanic pressure exceeds the intracranial pressure , and air is forced into the cranial cavity . when the intracranial pressure exceeds the pressure within the air collection , the one - way valve  closes , thus preventing the egress of the trapped air . in this mechanism , the abnormal air is usually distributed in the extradural space . in the presented case , pathologic deep and rapid respiration exerted additional pressure on the dural fistula allowing ambient air at a pressure above icp to drive itself into the intracranial space . the loss of csf from skull base fractures created a void space and relative negative pressure , allowing air to bubble in and fill the void . tp is rare condition and exceptionally rare when positive airway pressure has not been applied . in this particular case , the vacuum and one - valve effects were instead accentuated by a pathological pattern of respiration due to severe ketoacidosis and have caused tension pneumocephalon . written informed consent was obtained from the patient for publication of this case report and accompanying images . dr . frederikke rosendal has found the case and written the case report part of the article . shima bjerrum has written the rest of article along with the title page and has contact with the patient .