Teratomas are a group of tumours exhibiting evidence of simultaneous differentiation along endodermal, mesodermal, and ectodermal lines.
Morphologic features of teratomas are not directly related to their behavior.
Mature teratomas interpretated as benign, commonly behave in a malignant manner and metastasize.
By contrast, teratomas in infants and children with foci of undifferentiated cells are uniformly benign.
Teratoma may occur at any age.
Mature teratomas are composed of a haphazard array of differentiated mesodermal (Example: Muscle ; Cartilage ; Adipose tissue) , ectodermal (Example: Neural Tissue ; Skin) and endodermal (Example: Gut ; Bronchial epithelium) elements.
Mature teratomas are more common in infants and children.
Diagnosis of pure testicular teratoma should be made with extreme caution in adults, owing to the likelihood of concomitant malignant germ cell elements elsewhere in the tumour.
Immature teratoma: Immature teratomas contain elements of three germ layers in incomplete stage of differentiation. They should be regarded as malignant, even though cytologic features of malignancy may be inconspicuous.
Malignant teratoma: Malignant teratomas is characterized usually in the form of a carcinoma (Example: Squamous cell carcinoma ; Adenocarcinoma) developing within a mature teratoma.
Gonadal teratomas: a review and speculation. Adv Anat Pathol.2004 Jan;11(1):10-23.
Teratomas of the ovary and testis are confusing because, despite histologic similarities, they exhibit different biologic behaviors, depending mostly on the site of occurrence and the age of the patient. Thus, most ovarian teratomas are benign, and most testicular teratomas are malignant, with the exception of those occurring in children. These general statements, however, do not hold true for ovarian teratomas that are "immature" or exhibit "malignant transformation" and for dermoid and epidermoid cysts of the testis, categories of ovarian and testicular teratomas that are malignant and benign, respectively. This review concentrates on some of the "newer" observations concerning these interesting and confusing neoplasms, including diagnostically deceptive patterns. It is the author's opinion that much of the confusion regarding gonadal teratomas can be clarified by the concept that the usual ovarian teratoma derives from a benign germ cell in a parthenogenetic-like fashion, whereas the typical postpubertal testicular example derives from a malignant germ cell, mostly after evolution of that originally malignant cell to an invasive germ cell tumor (ie, embryonal carcinoma, yolk sac tumor, etc). The postpubertal testicular teratomas can therefore be thought of as an end-stage pattern of differentiation of a malignant germ cell tumor. The pediatric testicular teratomas, as well as dermoid and epidermoid cysts of the testis, however, must derive from benign germ cells, in a fashion similar to most ovarian teratomas. The teratomatous components of mixed germ cell tumors of the ovary, on the other hand, likely have a pathogenesis similar to that of postpubertal testicular teratomas.
Dermoids, which are the most common teratomatous lesion in the ovary, constitute only a small minority of testicular teratomas. The diagnosis should be reserved for lesions that are grossly typical of a dermoid cyst and are unassociated with adjacent intratubular germ cell neoplasia unclassified. The more common mature teratoma that has a malignant potential has a solid and cystic gross-sectioned surface contrasting with the predominantly cystic nature of the dermoid cyst.
Dermoid cyst of the testis: a study of five postpubertal cases, including a pilomatrixoma-like variant, with evidence supporting its separate classification from mature testicular teratoma.Am J Surg Pathol. 2001 Jun;25(6):788-93.
It is controversial if the rare dermoid cyst of the testis should be classified as a variant of mature teratoma or separately. The spectrum of findings is also ill defined, as is the relationship of dermoid cyst to intratubular germ cell neoplasia of the unclassified type (IGCNU). This study therefore reports the findings in five testicular dermoid cysts that occurred in five patients, 17-42 years of age, who presented with testicular masses. Four lesions consisted of a keratin-filled cyst with a thickened wall, whereas one had islands of "shadow" squamous epithelial cells with superimposed calcification and ossification (pilomatrixoma-like variant). Hair was identified grossly in two cases. On microscopic examination, four tumors had hair follicles with sebaceous glands showing a typical, cutaneous-type orientation to an epidermal surface, although no hair shafts were present in two. In addition, the fibrous wall contained smooth muscle bundles (all tumors) and eccrine or apocrine sweat glands (4 tumors). In some cases there were also glands lined by ciliated epithelium (4 tumors, including the pilomatrixoma-like variant), intestinal mucosa (1 tumor), and bone (2 tumors). There was no cytologic atypia or apparent mitotic activity, and no case had IGCNU in the seminiferous tubules. All patients were clinical stage I and were treated by orchiectomy without adjuvant therapy. All were well on follow-up from 1.5 to 9.5 years later. This study supports that dermoid cyst may have noncutaneous teratomatous elements and that an important criterion for its diagnosis is the absence of IGCNU. It also supports that it should be categorized separately from mature testicular teratoma because of the malignant nature of the latter in postpubertal patients. These observations suggest that there are at least two pathways for testicular teratomas in postpubertal patients: the more common being through IGCNU by differentiation from an invasive malignant germ cell tumor and the less common one, taken by dermoid cyst, by direct transformation from a nonmalignant germ cell.
The biologic behavior of teratomas is quite variable, depending on the pubertal status of the testis. In prepubertal testes, pure teratomas are considered benign even when they are histologically immature. This benign behavior has led some investigators to recommend a testis-sparing tumor enucleation rather than orchiectomy. However, such conservative treatment is not an option for teratomas in postpubertal testes. Of important distinction, every element in a postpubertal testicular teratoma (mature or immature) can metastasize, irrespective of its histologic characteristic.