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Fig. 1.95 Yolk sac tumour of nasal cavity. Typical features of yolk sac tumour, with many hyaline globules.
Fig. 1.96 Teratocarcinosarcoma. A Immature blastematous and glandular components are covered by a mixture of mature ciliated, mucinous and squamous epithe-lia. B Foci of neural differentiation showing fibrillary matrix and ganglion-like cells.

Histopathology

There are multiple tissue types derived from two or three germ layers, exhibiting variable degrees of maturity. In addition, there are intermingled carcinomatous and sarcomatous components {755, 2319}. The epithelial component is usually made up of keratinizing and nonkera-tinizing squamous epithelium, pseudos-tratified columnar ciliated epithelium, and glandular structures lined by either cuboidal or columnar cells that may show mucous differentiation. Nests of immature squamous cells containing clear cells (fetal-appearing) are a common finding and an important diagnostic clue {1042}. The carcinomatous component is usually glandular, but sometimes squamous. Neuroepithelial elements with rosettes and neuroblastoma-like areas are present in most instances. The mes-enchymal areas range from immature tissues (such as cartilage) to sarcomas (such as rhabdomyosarcoma and fibrosarcoma). There may be a proliferation of small round cells that are difficult to classify.

Immunoprofile

The undifferentiated/primitive component often shows positive immunoreaction for CD99 and occasionally synaptophysin and S-100 protein {1970}. The spindle cell component is consistently positive for vimentin, and sometimes desmin, myoglobin, and glial fibrillary acidic protein. The neuroepithelial component is positive for neuron-specific enolase and occasionally chromogranin, alfa-fetopro-tein, and cytokeratin. The epithelial component is positive for cytokeratins, epithelial membrane antigen, and occasionally S-100 protein and glial fibrillary acidic protein.

Differential diagnosis

Inadequate sampling may lead to erroneous diagnoses of olfactory neuroblas-toma, squamous cell carcinoma, undifferentiated carcinoma, adenocarcinoma, malignant salivary gland-type tumours and adenosquamous carcinoma {1042}.

Histogenesis

The tumour is unlikely to be of germ cell origin, but probably arises from a primitive cell in the olfactory/sinonasal membrane that not only reproduces the neu-roectodermal features of olfactory neu-roblastoma, but also has the capacity to differentiate into divergent types of somatic cells {1970}.

Prognosis and predictive factors

Teratocarcinosarcomas are highly malignant. They are locally aggressive, rapidly invading soft tissue and bone as well as the orbit and cranial cavities. They also have the potential to metastasize to regional lymph nodes and distant sites, mainly the lungs. The average survival is less than 2 years, with 60% of the patients not surviving beyond 3 years {1042}. Recurrences usually appear within 3 years.

Mature teratoma

Teratoma is the principal benign germ cell tumour of the sinonasal region and shows histologic features similar to its

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Fig. 1.97 Teratocarcinosarcoma. A The adenocarcinoma is intimately associated with the sarcomatous portion, arranged in a "teratoma-like" distribution. Cytologic atypia is present in both constituents of the neoplasm. B A primitive blastema-like component is immediately adjacent to a malignant glandular element that is juxtaposed with a malignant, cellular spindle cell constituent. C An adenocarcinoma with primitive blastema-like cells (left). The primitive cells can sometimes be arranged in a true rosette, similar to teratomas.

counterparts in the gonads and in other extragonadal locations.

Definition

Tumour composed of a variety of mature tissues that are foreign to the site of occurrence. There are typically tissues derived from two or three germ layers.

ICD-O code

9080/0

Synonyms

Teratoid tumour, benign teratoma. Epidemiology

Teratomas of the head and neck account for only 6% of all teratomas {2558}. Mature teratomas in the sinonasal tract are even more uncommon {955}. Most cases occur in neonates and older infants, with equal sex distribution {955,1737}. Stillbirth, prematurity, fetal malpresentation, dystocia, and maternal polyhydramnios are frequent associations.

Localization

In the sinonasal tract, the maxillary antrum and nasal cavity are affected more often than the sphenoid sinus {1036,1408,1778,1805,2312}. The nasopharynx can also be the primary site of involvement.

Clinical features

Facial deformity, nasal obstruction, and a nasal mass are common manifestations. Occasional calcifications may be seen on imaging {955,1805}. Teratomas may be associated with other skull deformities, anencephaly, hemicrania, and palatal fissures {8}.

Macroscopy

The tumours are usually cystic, but can be solid or multilocular. They are commonly encapsulated masses that measure up to 7 cm.

Histopathology

Teratomas are composed of variable admixtures of mature skin, skin appendages, fat, glial tissue, smooth muscle, cartilage, bone, minor salivary glands, respiratory epithelium and gastrointestinal epithelium. Neural tissues are seen more often in sinonasal ter-atomas than in teratomas of other sites. Although the variegated histologic appearance of mature teratomas is usu-

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