Cluster headache: to scan or not to scan.

By definition, cluster headache (CH) is not caused by underlying structural pathology. However, patients with CH or CH-like syndromes and an associated structural lesion have been described. In many cases it is difficult to establish a causal relation between the headache syndrome and the lesion. We reviewed the literature for symptomatic CH or CH-like cases in which causality was very likely, and we found that even typical CH with a typical episodic time pattern and a response to typical CH treatment can be caused by underlying structural pathology such as a pituitary tumor. Based on this small retrospective series of case reports, it is impossible to give advice about neuroimaging. If neuroimaging is considered, MRI (not CT) is the investigation of choice.