Brain Diseases [Disease/Finding] Headache Disorders [Disease/Finding] C0393735 M0328324 Headache Syndromes 230461009 Headache Disorders 1023986 N0000004182 Various conditions with the symptom of HEADACHE. Headache disorders are classified into major groups, such as PRIMARY HEADACHE DISORDERS (based on characteristics of their headache symptoms) and SECONDARY HEADACHE DISORDERS (based on their etiologies). (International Classification of Headache Disorders, 2nd ed. Cephalalgia 2004: suppl 1) C8542 D020773 Headache Disorders Cephalgia Syndromes