Section I Introduction.- 1 Perineum: Surgical Anatomy and Physiology.- 2 MRI Anatomy of the Anorectal Region.- 3 Ultrasound Anatomy of the Anorectal Region.- Section II Perianal inflammatory diseases.- 4 Crohn\'s Disease.- 5 Ulcerative colitis.- 6 Cryptogenetic Fistulas.- 7 Sexually Transmitted Diseases.- 8 Cancer in Perianal Fistulas.- Section III Clinical Examination and Medical Needs.- 9 Clinical Examination.- 10 Surgical Examination Under Anesthesia.- Section IV Ultrasound.- 11 Techniques.- 12 Crohn\'s Disease.- 13 Ulcerative Colitis.- 14 Cryptoglandular Fistulas.- 15 Cancer in Perianal Fistulas.- 16 Rare Diseases.- 17 Artifacts and Pitfalls.- Section V Magnetic Resonance Imaging (MRI).- 18 MRI Study Protocol.- 19 Dynamic MRI and the Assessment of Activity.- 20 Perianal Crohn\'s disease MRI classification and staging.- 21 Diagnostic Accuracy of MRI in Perianal Crohn\'s Disease.- 22 Post-surgical Findings and Post-treatment MRI Follow-Up.- 23 Ulcerative Colitis and Ileal Pouch Surgery.- 24 Cryptogenic Fistulas.- 25 Sexually Transmitted Diseases.- 26 Cancer in Perianal Fistulae.- 27 Rare Diseases.- 28 Artifacts and Pitfalls.- 29 Techniques and Role of CT in Perianal Disease.- 30 Integration of Diagnostic Modalities and Diagnostic Algorithms.