Sacrococcygeal Region: The body region between (and flanking) the SACRUM and COCCYX.Coccyx: The last bone in the VERTEBRAL COLUMN in tailless primates considered to be a vestigial tail-bone consisting of three to five fused VERTEBRAE.Pilonidal Sinus: A hair-containing cyst or sinus, occurring chiefly in the coccygeal region.Sacrum: Five fused VERTEBRAE forming a triangle-shaped structure at the back of the PELVIS. It articulates superiorly with the LUMBAR VERTEBRAE, inferiorly with the COCCYX, and anteriorly with the ILIUM of the PELVIS. The sacrum strengthens and stabilizes the PELVIS.Chordoma: A malignant tumor arising from the embryonic remains of the notochord. It is also called chordocarcinoma, chordoepithelioma, and notochordoma. (Dorland, 27th ed)Teratoma: A true neoplasm composed of a number of different types of tissue, none of which is native to the area in which it occurs. It is composed of tissues that are derived from three germinal layers, the endoderm, mesoderm, and ectoderm. They are classified histologically as mature (benign) or immature (malignant). (From DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1642)Perforator Flap: A mass of tissue for transplantation that includes the skin and/or the SUBCUTANEOUS FAT, and the perforating blood vessel that traverses the underlying tissue to supply blood to the skin. Perforator flaps are named after the anatomical region or muscle from where they are transplanted and/or the perforating blood vessel.Spinal Neoplasms