An 18-year-old male patient attended the emergency department for severe headache and headache referred by his GP due to the lack of improvement with conventional treatment for viral upper respiratory infections. His personal history included only a history of infectious mononucleosis. After a week of catarrhal symptoms, with general malaise, dry cough and fever (up to 38.5 ºC), he developed a global headache, more intense at the frontal level, in the last 48 hours, initially without rhinorrhoea or nasal obstruction. Isolatedly, he presented minimal purulent nasal discharge that was occasionally bloody in the last few days. He did not present loss of consciousness, convulsions, shivering or chills.
Physical examination revealed: temperature: 37.5ºC; BP: 137/73 mmHg; P: 71 bpm. Good general appearance with correct hydration and muco-cutaneous perfusion. No signs of illness. Febrile facies. No painful spots on percussion of the paranasal sinuses. On the skin there was a macular and erythematous rash affecting the trunk and neck. There were no palpable larynocervical, axillary or inguinal adenopathies. Cardiac auscultation was rhythmic, with no murmurs. Pulmonary auscultation shows a preserved vesicular murmur, without the presence of rhonchi, crackles or wheezing. The abdomen is soft, depressible and there are no palpable masses or megaliths. The upper and lower extremities are free of pathological findings, with distal pulses present. The neurological examination was strictly normal, with no evidence of focality or meningismus.
The corresponding complementary examinations were carried out, with a rigorously normal chest X-ray, non-pathological urine analysis and a haemogram showing leukocytosis with the presence of young forms (keys: 4%), making it necessary to consider the differential diagnosis between sinusitis and meningitis; therefore, a lumbar puncture was performed with 3 predominantly lymphoid cells and 0.3 g/dl of protein and no glucose consumption. At the same time, a radiographic study of the paranasal sinuses showed no data compatible with sinusitis; then, to rule out intracranial complications (such as cavernous sinus thrombosis / encephalitis), a cranial CT scan was performed, which showed occupation of the left sphenoid sinus, which was related to acute sinusopathy.

Once the diagnosis of sphenoidal sinusitis was confirmed, it was decided to admit the patient to hospital for proper monitoring of the patient's evolution and to start intravenous antibiotic treatment with third generation cephalosporins, treatment with which the patient evolved correctly, without complications, with the headache and fever subsiding within 48 hours and being asymptomatic at the time of discharge from hospital.