**2.3 Histology**

*Basic Principles and Practice in Surgery*

neum, head [2, 3].

with advanced age.

commonly identified.

Small: as 2–5 cm diameter Moderate: 5–10 cm Large: >10 cm.

**2.2 Classification**

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, retroperito-

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

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

Size of a SCT (average 8 cm diameter, range 1–30 cm) does not predict its

Antenatal diagnosis is important to avoid complications during delivery. Fetal US and MRI are the mainstay of antenatal diagnosis of SCT. MRI is more accurate in describing the intrapelvic and abdominal extent of the tumor and provides more information on compression of adjacent organs. Prenatal assessment of the fetus is critical for counseling the parents and planning surgical options. Because of acoustic shadowing by the fetal pelvic bones, US cannot always define the extent of SCT. Fetal MRI has been successfully performed to evaluate anatomy, content and extent of the tumor, but just a few small cases series have been published yet.

SCT arise from the base of the coccyx and may continuously grow in the posterior direction forming an external protrusion, or in the anterior direction, dissecting and distorting surrounding structures such as the rectum, vagina and bladder, but without invading them. Based on this morphologic characteristic, Altman et al.

biological behavior. Altman et al. defined the size of SCT as follows:

**58**

SCT are graded histologically as follows:

Grade 0—tumor contains only mature tissue

Grade 1—tumor contains rare foci of immature tissues

Grade 2—tumor contains moderate quantities of immature tissues

Grade 3—tumor contains large quantities of immature tissue with or without malignant yolk sac elements.
