Septal haematoma following nasal trauma is a complication that, if not diagnosed and treated early, may evolve into a nasal septal abscess. We present the case of a 10-year-old male who suffered nasal trauma with fracture and an undiagnosed septal haematoma that evolved into a septal abscess. During drainage of the abscess, necrosis of the quadrangular cartilage was noted. The patient later presented collapse of the nasal dorsum and deviation of the nasal septum. This sequela was corrected by means of an osteochondral costal graft. In the presence of any nasal trauma, it is important to explore the nasal septum correctly to discard the presence of a haematoma which, if not drained early, may evolve into an abscess due to compression of the quadrangular cartilage, leading to its necrosis in a few days and later collapse of the nasal dorsum as the child grows.