Acute sinusitis is an infection of the paranasal sinus cavities. The majority of infections are viral, and will resolve without treatment. Some infections are bacterial or will become bacterial over time (typically 7 - 10 days) and may require antibiotic treatment. Most bacterial infections are successfully treated with oral antibiotics, while a small percentage may require intravenous antibiotics. An even smaller number of patients may develop complications of an infection, including spread into the tissues around the eye and brain, and may require intravenous antibiotics and surgery.