Teratomas, Dermoids, and Epidermoids of the Head and Neck

Abstract Introduction

Cranial Epidermoid and Dermoid Inclusion Cysts Teratomas Summary

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Teratomas

Origins

Extragonadal teratomas, such as those of the brain, head, and neck, are thought to arise from misplaced, pluripotential, primordial germ cells. During normal embryonic development, typically by the end of the 3rd gestational week, uncommitted (pluripotential) germ cells are normally sequestered in the hindgut region of the yolk sac, near the allantois (7,17). These primordial germ cells remain relatively quiescent and "pure," while the other cells of the embryo undergo rapid proliferation with multiple cell division cycles. Later, when the embryo folds (in the 4th and 5th week of gestation), the previously sequestered germ cells migrate by ameboid movement back into the embryo along the dorsal (hindgut) mesentery of the yolk stalk to the urogenital ridge (7). Subsequently, during the 6th week, these germ cells develop into the spermatogonia or oogonia of the gonads.

Gonadal teratomas appear to arise, through some kind of parthenogenesis ("virgin birth"), from the unfertilized reproductive cells (eg, unfertilized ova) that are the haploid descendants of the embryonic germ cells. This theory is reinforced by chromosomal analyses demonstrating that the gonadal teratomas, although diploid, contain pairs of identical chromosomes, rather than the normal pairs of maternal and paternal chromosomes (7,18). Extragonadal teratomas appear to arise from diploid cells that do have a mixture of chromosomes from both parents, suggesting that they have an alternate derivation.

According to one theory, some of the embryonic germ cells fail to reach the gonadal ridge, become misplaced, or migrate aberrantly. These ectopic germ cells are usually embedded in or near midline structures and may be related to the head, mediastinum, or sacrococcygeal region. Without the normal cues for maturation, these ectopic germ cells retain their pluripotent capabilities and may develop into teratomas or any other type of germ cell neoplasm that might otherwise arise within a gonad (6). Another hypothesis suggests that since every cell contains the full genetic code, theoretically any somatic cell, without being a "germ" cell, could produce any other type of cell. Although this is one of the principles of cloning, it is a principle expressed more often in science fiction than in science fact. However, it allows an alternate theory of teratoma formation from ordinary somatic cells, rather than from uncommitted, pluripotent germ cells (6).

Regardless of their origin, teratomas are characterized by their pluripotential ability to produce virtually any adult tissue (mature teratoma) and fetal tissue (immature teratoma), including abortive organs, limbs, bones, and teeth.

Pathologic and Histologic Characteristics

Teratomas, by their nature, have varied, heterogeneous histologic characteristics (Figure 6). Mature teratomas may contain all manner of adult tissues with varying degrees of organoid development, whereas immature lesions may produce embryonal or extraembryonic fetal tissue. Lesions that show histologically divergent differentiation, even if derived from only a single germ layer, are also called teratomas. For example, a tumor with both skin and neural (neural tube or brain) differentiation is best classified as a teratoma, since it most probably arises from pluripotent cells.

Up to 90% of childhood teratomas contain derivatives from all three embryonic germ layers (6). Between 20% and 40% of childhood teratomas contain some immature tissues (1,8). Overall, neuroectodermal elements (both mature and immature) frequently dominate the childhood teratoma and are found more commonly in teratomas of the head and neck region (75% 85% have neural tissues), compared with sacrococcygeal teratomas (34% have neural tissues) (1,8). Bale et al (8) reported that up to 95% of childhood teratomas have some neuroectodermal elements, either mature or immature. Immature neuroectoderm might include regions that resemble the developing neural tube or cells that form primitive neuronal rosettes, similar to those seen in primitive neuroectodermal tumors (PNETs) such as neuroblastoma and medulloblastoma (Figure 7) (1,8). Thus, childhood teratomas with neuroectodermal elements may be confused with PNETs at histologic examination if there is inadequate tissue sampling. More important, the presence of some (<50%) immature neural tissue associated with a teratoma in a young child does not reduce the prognosis (8). However, when fetal neural tissues are not part of a teratoma or when they are found in an adult patient (with or without a teratoma), they are usually associated with a malignant behavior and a poor outcome.

Benign teratomas may contain either mature tissues or small amounts (up to 50%) of immature elements (7). Malignant extragonadal teratomas usually have carcinomatous features (eg, adenocarcinoma), rather than immature or embryologic components, and, as a group, they occur in older children (8). There are three types of malignant teratomas: teratoma with germ cell tumor (seminoma, embryonal carcinoma, choriocarcinoma, entodermal sinus tumor, or mixed), teratoma with nongerminal malignant tissue (carcinoma, sarcoma), and immature teratoma that metastasizes (7).

Both the pathologic and radiologic diagnosis of a teratoma may be suspected when a complex lesion contains fatty regions and calcifications. Calcification can be dystrophic, in areas of dead tissue, but may also occur as mineralization of osteoid matrix (true bone), cartilage, or well-formed teeth (Figure 8). Matrix calcifications may indicate divergent differentiation and thus are suggestive of teratoma. However, dystrophic calcifications can also occur in the lining of both dermoid and epidermoid inclusion cysts. A "fatty mass with calcification" could be either a teratoma or a dermoid, but is not likely to be an epidermoid cyst.

Clinical Presentation

The majority of extragonadal teratomas, including those of the head and neck, manifest during childhood, although they represent less than 5% of all pediatric neoplasms (19). Some authors have reported a bimodal distribution for craniofacial teratomas, with the biologically and histologically benign lesions seen in infants and children and malignant teratomas seen in older children and adults (7,20,21,22). In a review of the literature, Jordan and Gauderer (22) reported that only 10.6% of all cervical teratomas occurred in adults but 69% were malignant, compared with only 2.5% that were malignant in patients under 18 years of age.

Congenital tumors, when defined as those seen in the first 60 days of life, represent less than 3% of all pediatric neoplasms (1). However, teratomas are the most common of congenital tumors, accounting for up to 36% of all cases (1,23). Almost half (49%) of 254 childhood teratomas reported by Tapper and Lack (6) were found during the newborn period. Even though some teratomas are not congenital in terms of the patient's age at initial presentation, they may, nonetheless, be congenital in origin.

Childhood teratomas occur in primarily extragonadal locations, and the overwhelming majority of them are related to the spine, head, and neck (6,8,19,24). Most adult teratomas, by contrast, are gonadal. Overall, childhood teratomas are most commonly sacrococcygeal (59% 65%) (19,24); of those seen in the first 2 months of life, 82% are sacrococcygeal (8). The head and neck region is the second most common location for teratomas in early infancy, accounting for 5% 14% of those cases (6,8). In many series, the majority (75%) of head and neck teratomas (including intracranial lesions) are identified during the 1st year of life, and almost all those affecting the orbit and neck are noted at birth (6,8). Tapper and Lack (6), however, reported that the subset of intracranial teratomas usually manifests slightly later (median age at presentation, 2.5 years) than extracranial head and neck teratomas.

Sacrococcygeal teratomas have a female predominance of up to 87%, whereas craniofacial teratomas have an overall male-to-female ratio that varies from 1:1 to 2:1 (6,8). The intracranial teratomas of the pineal region have an unequivocal male predominance of up to 8:1 (16).

Most extracranial head and neck teratomas either are visible at birth or cause respiratory difficulty or feeding problems during the newborn period. Teratomas are occasionally diagnosed in utero at routine screening obstetric sonography. They may cause polyhydramnios (by interfering with fetal swallowing), and some fetuses will be too large for dates. Large craniofacial teratomas may interfere with labor and delivery (Figure 9, Figure 10). Intracranial teratomas are usually not grossly evident. However, in the case presented in Figure 8, the child had a simple dimple in the skin that led to a radiologic investigation. Even though all teratomas are probably of congenital origin, some do not manifest until later in life (Figure 11). Older patients with intracranial teratomas, unlike the infants with these lesions, may present with neurologic signs, developmental delay, seizures, and hydrocephalus.

Intracranial Teratomas

Intracranial teratomas can be divided into two broad categories: those that occur intraaxially in the cerebral hemispheres, are typically large, and are usually found in the newborn period, and those that manifest later, are more likely to be in the pineal region, and are usually smaller (16,23).

Of the intracranial neoplasms that manifest in the first 2 months of life, teratomas and PNETs are the most common, and each has a frequency of about 27% (23). Neonatal presentation of intracranial teratomas usually occurs because of problems during delivery or increasing head circumference (23). This type of teratoma is typically a large, heterogeneous, supratentorial mass within a cerebral hemisphere.

Often, these tumors may have characteristic imaging features, showing both lipid and calcification (Figure 8, Figure 9, Figure 10, Figure 11). Both teratomas and PNETs can have punctate foci of calcification, but the presence of lipid indicates a teratoma. PNETs can, however, contain the blood breakdown product methemoglobin, which can cause T1 shortening and mimic lipid. In addition, since clearly recognizable lipid is not always present in teratomas (Figure 11), teratoma cannot be excluded from the differential diagnosis if no fat signal is seen (23). In children older than a few months of age, the prevalence of cerebral teratoma decreases so much that a large hemispheric mass is more likely to be either a PNET or a glial tumor rather than a teratoma.

The survival of a patient with cerebral hemispheric teratoma depends directly on the degree of resectability and less on the histologic characteristics of the tumor.

The second group of intracranial teratomas usually occurs in older children (2-15 years of age) or young adults. These tumors are extraaxial masses, developing in either the pineal region or the suprasellar cistern (8). Teratoma is the second most common neoplasm of the pineal region; only the germinoma (seminoma) is more frequent. Both germinoma and teratoma are considered to arise from intracranial germ cell rests, and, in the older literature, pineal germinomas were erroneously called "atypical teratomas" and even "pinealomas," even though they are not derived from pineal cells (16).

Gender is not useful in the differential diagnosis of these two common pineal masses because both have a distinct male predilection (16). Pineal teratomas are usually multiloculated and have heterogeneous attenuation and signal intensity at CT and MR imaging (16). Germinomas are usually homogeneous on both CT and MR images, do not have attenuation or signal intensity characteristics similar to those of fat, and have homogeneous enhancement with contrast material. On CT scans, germinomas have homogeneously high attenuation.

In contrast to the cerebral (intraaxial) teratomas of infancy, pineal teratomas are usually histologically mature and may even be encapsulated. This latter characteristic facilitates surgical resection and prevents dissemination. By comparison, pineal germinomas are unencapsulated neoplasms that frequently seed the cerebrospinal fluid and usually require a combination of radiation therapy and chemotherapy, as well as surgical resection.

Orbital Teratomas

In contrast to the high frequency of orbital dermoid inclusion cysts, orbital teratomas are extremely rare (25). Orbital teratomas are usually benign and well differentiated histologically (7), but they may be enormous, causing considerable facial deformity and disfigurement with the need for reconstructive surgery after removal (Figure 12). As with teratomas in other locations, they are usually heterogeneous masses, with calcification, fatty regions, and occasional bone formation. They may be sharply circumscribed. If they are posterior to the globe, they can cause substantial deformity and remodeling of the bony orbit cavity, especially when they are present at birth. Orbital teratomas are usually multiloculated, cystic masses with solid areas, rather than unilocular cystic lesions such as dermoid and epidermoid inclusion cysts. In addition, orbital teratomas have a complex intermingling of lipid and calcifications (Figure 12), rather than the single fat-fluid level characteristic of a dermoid cyst.

The differential diagnosis for an orbital mass with low attenuation values (those of water or below) includes hemangioma or lymphangioma, microphthalmia with cyst, coloboma and congenital cystic eye, epidermoid cysts, and meningoencephalocele (13). Hemangiomas and other vascular lesions, as well as most solid tumors (eg, rhabdomyosarcoma), typically show obvious enhancement after infusion of contrast material at CT, and they may have higher attenuation on unenhanced scans. Enhancement in a dermoid, if present, should be peripheral and ringlike, whereas a teratoma may have areas of patchy enhancement in the solid regions interspersed between the nonenhancing lipid and cystic areas.

The treatment of orbital teratoma is surgical resection and usually involves exenteration. The globe and optic nerve are almost always affected, and vision on the involved side is only rarely preserved. However, despite vision loss, the prognosis is excellent, since orbital teratoma is usually histologically benign and frequently encapsulated (7).

Teratomas of the Neck

Teratomas of the neck, nasopharynx, pharynx, and oral cavity are usually large, bulky masses that are clearly evident and recognized at birth (Figure 13, Figure 14, Figure 15). Many of these are diagnosed at routine prenatal ultrasound examinations. The primary differential diagnostic considerations for a large neck mass, either in a fetus or an infant, include cystic hygroma and congenital cysts of branchial cleft or thyroglossal duct origin. However, in older children, lymphoma and infectious lymphadenitis are also possibilities. Lingual teratomas (as well as dermoids and epidermoids) are extremely rare, with less than 20 cases reported in the English literature (6,26,27). A teratoma of the tongue (Figure 16), usually a midline mass, might be mistaken for more common lesions, including a thyroglossal duct cyst, a mucus retention cyst, ectodermal inclusion cysts, or lingual thyroid tissue (26).

Knowledge of the embryologic development can be invaluable in the differential diagnosis. The normal thyroid arises from an invagination of entoderm at the foramen cecum; from there it descends in the neck past the hyoid bone to develop anterior to the cricoid cartilage and the trachea (28). The thyroglossal duct cyst follows the embryologic course of the duct: It may begin at the foramen cecum, pass inferiorly to hook around the anterior aspect of the hyoid bone, and then pass downward toward the thyroid isthmus, most typically embedded within the strap muscles (28). In the past, many cervical teratomas were described as having a thyroid gland origin, merely because they contained thyroid tissue. However, the derivation of cervical and thyroid teratomas from either the thyroglossal duct or from the pharyngeal pouches (ultimobranchial anlage) remains controversial (29,30).

Cervical teratomas frequently contain some thyroid tissue, which can confuse the pathologist, especially since a cystic tongue mass is much more likely to be a thyroglossal duct cyst rather than a teratoma. The thyroglossal duct cyst is a fluid-filled cystic remnant of the embryonic thyroglossal duct. These cysts will have foci of normal thyroid tissue in the wall in up to one-third of cases, and, in less than 1%, there will be a thyroid carcinoma in the cyst wall (28).

A teratoma can be suspected when a multiloculated lesion with focal areas of low attenuation and high signal intensity (representing lipid) is seen on CT and T1-weighted MR images, respectively (Figure 13, Figure 15). Radiologically evident lipid may be scattered throughout the mass, rather than forming a single, large collection or fat-fluid level (Figure 15) that might suggest a dermoid inclusion cyst. The developmental cysts of the branchial cleft and thyroglossal duct are also more often unilocular, with only a thin rim of enhancement, and do not contain fat. Occasionally, these cysts appear septated and therefore mimic a multiloculated teratoma. Thyroglossal duct cysts tend to be oblong or roughly tubular, oriented vertically along the path of the normal embryologic migration of those structures. Within the tongue, they are usually in the posterior one-third or the base. The lingual teratoma illustrated in Figure 16 resembles a thyroglossal duct cyst, but it is multilocular and somewhat more anterior within the tongue muscles than the embryologic course of the thyroglossal duct.

Abstract Introduction

Cranial Epidermoid and Dermoid Inclusion Cysts Teratomas Summary

Source Information References