The<unk>  may contain one of several kinds of tumor. The most common tumor here is sacrococcygeal teratoma. Others are retrorectal hamartoma (tailgut cyst), schwannoma, ganglioneuroma, and ependymoma. Also sometimes found here is an anterior meningocele, a relatively mild form of neural tube defect. Causes of increased<unk>  are: ulcerative colitis, granulomatous colitis, lymphogranuloma venereum, and in postirradiation changes, thrombosis of the inferior vena cava and tuberculous proctitis, tumor of the sacrum or posterior wall of the rectum. Carcinomatous deposits in the pelvis can also cause<unk>  widening.<unk>  edema is common in patients with heart failure who are confined to bed.
Presacral space
Supracristal plane
Radial plane
Muscular triangle
Costovertebral angle
Mid-inguinal point
Suboccipital triangle
Pocock boundary