**2.1 Etiology**

SCT arises from pluripotent cells of Hense's node that is present/located anterior to coccyx, a remnant of the primitive streak in the coccygeal region. The primitive

streak is a longitudinal ridge of ectodermal cells at the caudal end of the bilaminar embryonic disc. It consists of totipotent cells, which are able to transform into any type of cells. This structure determines the future craniocaudally axis of the embryo and demarcates the embryo into left and right halves. If totipotent cells of the primitive streak remain after the fourth week, these cells give rise to a SCT [1].

SCT is a relatively uncommon tumor affecting neonates, infants and children.

SCT represents a group of benign and malignant tumors deriving from the primordial germ cells. Pediatric germ cell tumors (GCTs) are neoplasms derived from primordial germ cells and may occur both inside the gonads and extragonadal organs. The five main histologic categories of GCTs are: dysgerminomas (in the ovary), seminomas (in the testes), teratomas, choriocarcinomas and endodermal sinus tumor (ESTS) or Yolk sac tumor. The most common site of extragonadal GCTs in the pediatric population is the sacrococcygeal region and the most common type are teratomas.

The sacrococcygeal region is the most frequent location for teratomas, but teratomas may occur in almost any organ, tending to develop more commonly in midline or paraxial location and can be observed from the brain (cephalad) to the coccyx (caudal). Less common sites are the mediastinum, testes, ovary, retroperitoneum, head [2, 3].

Females are affected more frequently with a female to male ratio of almost 4:1.78. SCT are either mature, immature or malignant, composed of embryonic elements. A mature SCT is a benign tumor containing only mature components, while immature SCT contains immature tissues. SCT that contains malignant elements are considered to be malignant tumors. Mature and immature teratomas are considered as benign tumors and may undergo malignant transformation. At birth, the great majority of SCTs are benign. They can manifest malignant transformation with advanced age.

They appear as cystic tumors or solid. The cystic may be filled with serous fluid, mucoid or sebaceous material, or even cerebrospinal fluid. Virtually any tissue can be present in a SCT. Neuroglial tissue, skin, respiratory and enteric epithelium cartilage, smooth muscle and striated muscle fibers are the most common elements found. Also bone, pancreatic tissue, choroid plexus and adrenal tissues are less commonly identified.
