In many cases, acute mastoiditis is manageable with intravenous antibiotics and hospitalised care. However, the decision whether to intervene surgically remains crucial and reliance is based on radiological findings – CT scans for bony changes and MRI for possible intra-cerebral complications. In this illustrative article, the authors have mentioned a 16-point checklist to help the otolaryngologist to pick up possible complications of acute mastoiditis from CT scans and MRI. The checklist comprises more common complications involving the temporal bone, such as ossicular involvement, pars flaccida cholesteatoma and tegmen erosion, and goes on to include several extratemporal involvements such as brain abscesses, sinus thrombosis, meningeal and vascular involvements. It also incorporates Bezold’s and Luc’s abscesses and temporomandibular joint involvement. Anatomical variations that may affect surgery are mentioned, such as an unsuspected high jugular bulb which may come in the way of a simple myringotomy! This comprehensive list with illustrations and pathological explanations provides a handy and practical ‘ready reckoner’.