Pneumoencephalia is a rare disorder in veterinary medicine and defined as the presence of air between or in any brain compartments (like ventricular, paranchimal, subarachnoid, subdural). Its most often causes are cranial trauma or surgeries like rhinotomy or craniotomy. In humans it is mostly shows no symptoms, doesn’t requires any intervention and resolves spontaneously after two to five days. Altough in some cases it can cause symptoms like epileptic seizures, loss of consciousness, nausea, vomiting, dizziness and paralysis. This is called “tension pneumoencephalia”.In this case, 8 year old dog was referred because of sneezing, reverse sneezing and sanguineus discharge from both nostrils and right eye. After the initial evaluation, a mass in the nasal cavity was identified by Computed Tomography and dorsal rhinotomy was performed for its complete removal. The biopsy material was sent for histopathological examination and the result was Adenocarcinoma. In follow up after ten days from surgery the patient shows no abnormalities and radiation therapy was suggested as the therapy of choice for Adenocarcinoma. After five days from follow-up, the patient referred again to our clinic because of neurological symptoms like imbalance, vomiting, anorexia, spinning around on its own axis and agression towards the owner. After the examination, cranium CT and Magnetic Resonance Imaging shows pneumoencephalia in lateral ventriculi, lysis of cribriform plate lysis and herniation of the bulbus olfactorius in the right side. The neurological symptoms of this case was resolved completely after three days of medical treatment towards intracranial pressure, oedema and possible seizure activity. After four months post-op follow up examination also shows no abnormalities in this case’s patient. As result, patients needs to be monitorized after sinonasal tumor surgery for possible neurological symptoms and pneumocephalia. If the pneumocephalia exists but it doesn’t cause any neurological symptoms, it can be treated conservatively without surgery.