halo sign

1. a halo effect produced in the radiograph of the fetal head between the subcutaneous fat and the cranium; said to be indicative of intrauterine death of the fetus. 2. a sign of cerebrospinal fluid in rhinorrhea: a drop of bloody nasal discharge is placed on a cloth; if it contains cerebrospinal fluid, there will be a light-colored ring radiating out farther than the blood. 3. an early computed tomographic finding in pulmonary aspergillosis, consisting of a ring of ground-glass opacity surrounding a primary nodule; it is occasionally seen in other pulmonary conditions, including mycoses, carcinoma, and pneumonia.