The presence of gas in the cranial cavity is called “pneumocephalus”, and is usually seen after invasive surgical procedures. Although symptoms are non-specific, such as headache, it can cause neurological distortion, coma, and death. Oxygen therapy is the most effective way to treat pneumocephalus and accelerates the reabsorption of the air. Hyperbaric oxygen treatment (HBOT), with its direct high pressure effect, causes the air mass to shrink. In the case reported in this paper, the pneumocephalus manifested with the symptom of sudden loss of consciousness and the etiology was an invasive intervention of dialysis catheter placement while the patient was in a sitting position. HBOT was applied as an emergency treatment, after which a dramatic radiological improvement was detected with computed tomography. Although this patient needed consecutive HBOT sessions for the best result, only a single session of HBOT could be applied because she was under the observation in the intensive care unit of another hospital due to the lack of space in the intensive care unit of our hospital. One of the main points is that the clinicians should not decide to cease HBOT only after the first session. Consecutive HBOT sessions can dramatically improve the radiological and clinical findings in these case