Pathology of teratoma

Teratoma is a neoplasm of germ-cell origin that is composed of several types of tissue

* Corresponding author. Department of Urology, Sidney Kimmel Center for Prostate and Urologie Cancers, 353 East 68th Street, New York, NY 10021. E-mail address: [email protected] (J. Sheinfeld).

representing different germinal layers (endoderm, mesoderm, ectoderm), forming somatic-type tissue in various stages of maturation and differentiation. Based on findings of genetic studies, it is now recommended to consider teratoma as a single entity regardless of the degree of maturation and differentiation of the tissue comprising it [5]. Infantile teratomas are diploid and follow a benign course. Genetic studies (karyotyping and comparative genomic hybridization) tumors have failed to demonstrate chromosomal changes in these tumors. In contrast, teratomas in adult testes are hypotriploid and have genetic changes similar to those seen in other components of GCTs.

On gross examination, teratomas are usually nodular and firm with a variably cystic and solid cut surface. The cysts may be filled with keratinous material or clear serous or mucoid fluid. The solid areas may contain translucent, gray-white nodules representing cartilage. Hair or melanin-containing tissue may also be rarely seen. Areas of immature tissue are mostly solid and may have an encepha-loid, hemorrhagic, or necrotic appearance.

Fig. 1 demonstrates the microscopic appearance of the various histologic subtypes of tera-toma. Microscopically, mature elements contain well-differentiated tissues resembling normal postnatal tissue and typically including structures derived from the three germ layers. Tissue of ecto-dermal origin maybe represented by nests of squa-mous epithelium with or without cyst formation and keratinization. Neural tissue may be encountered as foci of neuroglia. Structures of endodermal origin are represented by glandular epithelium of enteric or respiratory type. Other glandular tissue such as pancreatic, mucus-producing, prostate, and thyroid may be found. Mesodermal elements are represented by cartilage,

Neonatal Kidney

Fig. 1. Teratoma with various types of mature tissue elements including enteric-type epithelium, cartilage, smooth muscle, and adipose tissue (A). Teratoma with immature tissue elements resembling fetal-type cartilage and undifferentiated mesenchyme (B). Teratoma with somatic-type malignancies: rhabdomyosarcoma (C) and primitive neuroectodermal tumor (D).

Fig. 1. Teratoma with various types of mature tissue elements including enteric-type epithelium, cartilage, smooth muscle, and adipose tissue (A). Teratoma with immature tissue elements resembling fetal-type cartilage and undifferentiated mesenchyme (B). Teratoma with somatic-type malignancies: rhabdomyosarcoma (C) and primitive neuroectodermal tumor (D).

bone, adipose tissue, fibrous tissue, and, most commonly, muscle. Attempts at organ formation are frequently identified with smooth muscle encircling glands of respiratory or enteric morphology.

Immature, fetal-type tissue may also consist of ectodermal, endodermal, and/or mesodermal elements. It usually occurs as islands of immature neuroepithelium resembling that of the developing embryonic neural tube. Immature tissue may also have an organoid arrangement with blastematous and primitive tubular structures resembling that of the developing kidney or lung. Embryonic skeletal muscle, cartilage, and nonspecific cellular stroma may also be encountered. There is no point, however, in grading the degree of immaturity in such tumors in adults because they derive from invasive malignant GCTs and they may have metastases even if they appear totally mature.

Teratoma with somatic-type malignancies refers to the development of independently evolving, malignant neoplasms of the type typically encountered in other organs and tissues, eg, sarcomas and carcinomas. Usually derived from one of the teratomatous elements, these tumors are characterized by an invasive or expansile proliferation of malignant cells that overgrow the surrounding GCT. The most common somatic-type malignancy seen in GCT is sarcoma of various types, particularly those of striated muscle differentiation (ie, rhabdomyosarcoma). Primitive neuroectodermal tumors have also been increasingly identified in association with GCT. Adenocarcinomas, squamous carcinomas, and neuroendocrine carcinomas may also be associated with GCT.

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