The authors present a rare case of treatment complications in a 12-year-old spayed female Shiba Inu with left nasal transitional cell carcinoma. To control the tumour, the authors performed hypofractionated radiotherapy for five fractions over 1 week, combined with surgery, acridine orange photodynamic therapy (AO-PDT) and cribriform irradiation, one month after the initial radiotherapy. Six months later, the dog presented with neurological abnormalities (circling, pacing and reduced consciousness). Pneumocephalus was diagnosed. The irradiated left side of the olfactory bulb had become necrotic; therefore, surgery was performed to close the hole of the cribriform plate. Two years later, no visible radiation side effects or clinical signs related to intranasal tumour recurrence were detected. This case suggests that hypofractionated radiotherapy followed by surgery, AO-PDT and cribriform irradiation can contribute to tumour control. However, rare side effects, such as pneumocephalus, should be considered. Therefore, patients should be monitored carefully for adverse events after this combination.