Occasionally, radiologically diagnosed acute appendicitis is found to harbour underlying appendiceal neoplasm on post-surgical histopathology. Conversely, a situation in which radiologically, the appendix demonstrates features consistent with an underlying tumour but post-operative pathology finds no evidence of neoplastic change is rare. We describe a case of a 50-year-old man who presented with a markedly dilated "mass-like" appendix with minimal inflammatory changes on a computed tomography scan. Radiological findings were suspicious for an appendiceal neoplasm/mucocele (i.e. low-grade mucinous neoplasm). However, the post-surgical histopathological diagnosis did not concur with the radiological diagnosis and instead demonstrated findings compatible with acute appendicitis without neoplastic change. In this case report we provide a histopathological correlation and an explanation as to how this may have happened with the hope of helping radiologists avoid this pitfall in the future.