DOI: 10.1148/rg.251045156
RadioGraphics 2005;25:215-242
From the Archives of the AFIP
A Comprehensive Review of Fetal Tumors with Pathologic Correlation1
Paula J. Woodward, MD,
Roya Sohaey, MD,
Anne Kennedy, MD and
Kelly K. Koeller, Capt, MC, USN
1 From the Department of Radiologic Pathology, Armed Forces Institute of Pathology, Bldg 54, Rm M-121, 14th and Alaska Ave NW, Washington, DC 20306-6000 (P.J.W.); Oregon Health Science University, Portland, Ore (R.S.); University of Utah, Salt Lake City (A.K.); and Armed Forces Institute of Pathology, Washington, DC (K.K.K.). Received August 5, 2004; revision requested October 6 and received October 19; accepted October 19. All authors have no financial relationships to disclose. Address correspondence to P.J.W. (e-mail: woodwardp@afip.osd.mil).
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Abstract
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Fetal tumors are a diverse group of neoplasms, which are unique in their histologic characteristics, anatomic distribution, and pathophysiology. The biologic behavior of tumors in the fetus may differ dramatically compared with that of the same tumor detected later in life. Teratomas are the dominant histologic type and constitute the majority of both extracranial and intracranial neoplasms. Although often histologically mature, they may prove lethal because of their location and metabolic demands on the fetus. Large solid tumors may lead to cardiovascular compromise and hydrops fetalis. Extracranial teratomas are most commonly located in the sacrococcygeal area, followed by the head and neck, chest, and retroperitoneum. Fetuses with intracranial tumors have a poor prognosis regardless of histologic type. There are, however, two notable exceptions: lipomas and choroid plexus papillomas, both of which have a more favorable outcome. Neuroblastoma is the most common fetal malignancy. It may be either solid or cystic and is more often located on the right side. It typically has favorable biologic markers and stage at presentation. The prognosis for prenatally diagnosed cases is excellent. Other fetal neoplasms include soft-tissue tumors (both benign and malignant), leukemia, mesenchymal hamartoma of the kidney, and liver tumors (hemangioendothelioma, mesenchymal hamartoma, and hepatoblastoma).
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Describe the histologic types and biologic behavior of fetal tumors.
- Delineate those conditions in which prenatal intervention may improve outcome.
- Recognize pertinent imaging features, which help differentiate fetal tumors from the more common congenital malformations.
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Introduction
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Fetal tumors, although uncommon, pose a unique circumstance in the care of an obstetric patient and create significant medical and ethical dilemmas. Although the diagnosis of any fetal anomaly is a devastating event for a family, the presence of a fetal tumor carries with it additional diagnostic and therapeutic challenges. The prognosis is generally poor, although there are some notable exceptions. An understanding of the different tumor types and their biologic behavior is necessary for appropriate counseling and care of these patients. Accurate diagnosis has important implications for fetal, maternal, and neonatal care.
The true prevalence of fetal tumors is difficult to determine, as reporting practices vary widely among institutions. Although the reported prevalence for all congenital tumors is in the range of 1.7–13.5 per 100,000 live births, those tumors occurring in fetuses that are stillborn or aborted are most likely underreported in tumor registries (1–4). In addition, the definition of a congenital tumor varies among published series. Clearly, masses in the fetus and newly born infant are congenital. It is also generally agreed that tumors manifesting in the first month of life are also congenital, with some arguing that any tumor developing in the first 3 months of life should be regarded as congenital (1–4).
Controversy also exists about exactly which masses are categorized as congenital tumors. Many series exclude hamartomas, because these lesions contain histologically normal cells derived from the organ of origin. Hemangiomas and lymphangiomas are considered by many to be more appropriately categorized as congenital malformations, rather than true neoplasms. With the exclusion of these three masses, the most common fetal neoplasms are extracranial teratomas, neuroblastomas, soft-tissue tumors, brain tumors, and leukemia (2). Collectively, these tumors constitute approximately 85% of all congenital tumors, with renal tumors, liver tumors, and retinoblastomas constituting the majority of the remainder (4).
To further complicate matters, fetal tumors are truly different from those occurring in childhood; thus, knowledge of tumor type, distribution, and prognosis for tumors occurring in the pediatric population cannot be extrapolated to fetal tumors. Fetal tumors occur with different prevalence, anatomic locations, histologic characteristics, and biologic behavior, compared with pediatric tumors. Some fetal tumors, even though they are histologically benign, may prove fatal because of their size or location. Large benign masses may result in cardiovascular compromise and fetal demise. They may also exert substantial mass effect, inhibiting normal organ development or causing airway obstruction after delivery. The behavior of malignant tumors also cannot be predicted on the basis of known responses in pediatric patients. For example, congenital leukemia has a grim prognosis, whereas neuroblastoma has a more favorable outcome in the fetus and newborn than in older children (4).
The physiology of embryologic development adds to the uniqueness of fetal tumor behavior. No adult tumor grows as rapidly as a normally dividing embryo (4). Normal embryonic cells, with their high mitotic rate, share histologic features with neoplastic cells. One theory of fetal tumor development suggests they do not arise in a previously normally formed organ, as tumors do later in life. They may result from failure of developing tissues to undergo normal cytodifferentiation and maturation. A tumor would be the result of normal immature fetal tissue continuing to divide in an unrestricted fashion (4). Given the mitotic potential of embryonic cells, it is not surprising that fetal tumors (benign as well as malignant) demonstrate remarkable growth rates and reach enormous proportions. It is possible for a large mass to develop within weeks of a normal fetal ultrasound (US) survey (4,5).
Although individual tumors have their own unique characteristics, some features are common to all fetal tumors. Polyhydramnios is the most common, being present in approximately one-third of patients. It may be the first clinical sign, with increased fundal height being noted during an obstetric examination (3). Associated congenital anomalies are present in 20% of cases (particularly with teratomas), and hydrops is reported in 17% (3). If a fetal tumor remains undiagnosed before the onset of labor, the mother may present with dystocia, with the fetus being at significant risk for tumor rupture and exsanguination (4).
Widespread application of screening sonography has increased our awareness of fetal tumors. Doppler sonographic evaluation has advanced our understanding of the pathophysiology of these lesions and the accompanying fetal hemodynamic changes complicating the pregnancy. Magnetic resonance (MR) imaging is ideally suited for evaluation of fetal tumors by virtue of its large field of view and superior soft-tissue contrast. In addition, the rapid evolution of MR imaging technology has yielded fast, and now ultrafast, techniques that provide high-resolution imaging while virtually eliminating motion artifact without fetal sedation (6–13).
Accurate prenatal diagnosis is essential for appropriate planning of both prenatal and postnatal care. These complicated conditions require a multidisciplinary team composed of radiologists, perinatologists, neonatologists, pediatric surgeons, genetic counselors, and social workers. It is essential that we recognize which conditions may be improved with in utero treatment. It is equally important to recognize that our ability to diagnose often exceeds our ability to treat, and that in some cases the best option is to offer supportive care.
In this article, we review the clinical characteristics, imaging appearances, associated abnormalities, natural history, and potential treatments of the varied fetal tumors.
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Teratomas
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Teratomas form the most common and important group of fetal tumors. Unfortunately, their manifestation in fetal life can be quite dramatic. Teratomas typically occur along the midline of the body, anywhere from the coccyx to the pineal gland. This scattered occurrence is best explained by an aberration in the embryologic development of the gonads (4,14).
Primordial germ cells originate external to the embryo within the yolk sac wall. Between 4 and 6 weeks gestation, they migrate in an amoeba-like fashion along the hindgut and dorsal mesentery to the genital ridges located on either side of the midline. During the migration, primordial germ cells continue to undergo mitosis. Once at the genital ridges, they are incorporated into the primitive sex cords, which form from fingerlike projections of proliferating mesothelium (Fig 1). Together, the primitive sex cords and the primordial germ cells form the primitive gonad, which continues to differentiate into either an ovary or testis (14). During this migratory process, a few of the primordial germ cells may become isolated in an aberrant location. Under normal conditions, germ cells not invested by the sex cords will degenerate and die. Teratomas are thought to arise from unincorporated pluripotential germ cells, which fail to involute and continue to undergo mitosis (4,14).
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Figure 1a. Gonadal embryology. (a) Drawing of a 6-week embryo depicts migration of the primordial germ cells (red dots) from the yolk sac along the hindgut to the genital ridges. (b) Diagram of a midabdominal cross section shows incorporation of the primordial germ cells (red dots) into the primitive sex cords, which will continue to develop into either a testis or ovary. Unincorporated germ cells have the potential to form teratomas.
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Figure 1b. Gonadal embryology. (a) Drawing of a 6-week embryo depicts migration of the primordial germ cells (red dots) from the yolk sac along the hindgut to the genital ridges. (b) Diagram of a midabdominal cross section shows incorporation of the primordial germ cells (red dots) into the primitive sex cords, which will continue to develop into either a testis or ovary. Unincorporated germ cells have the potential to form teratomas.
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By definition, teratomas are composed of all three germ cell layers (ectoderm, mesoderm, and endoderm). Some of the histologic features of fetal teratomas are unique, compared with teratomas seen later in life. Ectodermal components, especially neural tissues, are a dominant feature of fetal teratomas. Mesodermal tissues including fat, bone, smooth muscle, and cartilage are also common. Endodermal components, generally consisting of respiratory epithelium and gastrointestinal tissues, are the least common (2–4).
Teratomas are histologically classified as either mature or immature, with the immature elements consisting principally of primitive neuroglial tissue and neuroepithelial rosettes (Fig 2) (2,3). In a minority of immature teratomas, malignant elements, predominantly yolk sac tumor or embryonal carcinoma, may be present (2). Immature elements are common in fetal teratomas, yet their presence does not carry the same poor prognosis that it does later in life. The immature histologic appearance may be more reflective of the immaturity of the fetus and not necessarily reflective of the biologic behavior of the tumor. The location and size of the mass are far more important than the histologic grade for predicting outcome. Fully resectable, immature teratomas in the newborn have a generally favorable prognosis (4).
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Figure 2. Immature teratoma. Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows ectodermally derived immature neuroglial tissue. Neuroepithelial rosettes (arrows) are seen in a background of cellular stroma.
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Sacrococcygeal Teratomas
The sacrococcygeal region is the most common site for teratomas, with 70%–80% of all teratomas being located in this region (1,2). The quoted prevalence is one in 40,000 live births with a female preponderance of 4:1 (4). The fetal prevalence is most likely higher, given the relatively high number of in utero deaths, stillbirths, or terminated pregnancies that may go underreported. The prognosis for a fetus with a sacrococcygeal teratoma is substantially worse than that for a neonate with this tumor. The mortality rate for infants with neonatally diagnosed sacrococcygeal teratomas is approximately 5%, whereas the mortality rate for fetuses with sacrococcygeal teratomas is nearly 50%, with fetuses whose tumors are diagnosed before 30 weeks gestation faring worse (15). The presence of hydrops, which develops from arteriovenous shunting and high-output cardiac failure, portends a grave outcome (16,17).
The initial sign of a fetal sacrococcygeal teratoma may be increased uterine fundal height. Increased uterine size may result from the mass itself or from associated polyhydramnios. Not all patients are symptomatic, with some sacrococcygeal teratomas being discovered during a routine obstetric sonogram. Most sacrococcygeal teratomas are diagnosed in the second trimester, but they have been detected as early as 13.5 weeks gestation (18). Failure to diagnose a fetal sacrococcygeal teratoma during pregnancy can have serious, and potentially catastrophic, consequences for the fetus and the mother. Complications include premature delivery, dystocia, intratumoral hemorrhage, or tumor avulsion with fetal exsanguination (19).
Sacrococcygeal teratomas are classified according to the American Academy of Pediatrics Surgery Section Survey into four types based on the amount of mass present externally versus internally (Fig 3). With type I sacrococcygeal teratoma, the mass is external with minimal or no internal components. Type II is predominantly an external mass with internal extension into the presacral space. Type III is an external and internal mass with extension into the abdominal cavity. Type IV is entirely internal with no external component (20). This system of classification has important prognostic implications in the pediatric population. Pediatric sacrococcygeal teratomas with an undiagnosed internal component are more likely to undergo malignant transformation, and complete resection is required (Fig 4). Malignant transformation of a sacrococcygeal teratoma occurs in 5%–10% of cases diagnosed before 2 months of age and increases to 50%–90% for those diagnosed at 2–4 months of age (15).
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Figure 3a. Classification of sacrococcygeal teratomas. (a) Type I. Coronal US image of a fetal spine shows a small, exophytic, cystic mass (straight white arrow) emanating from the coccyx (curved arrow). No internal component was identified. Black arrow = iliac crest. (b) Type II. Longitudinal US image of a lower fetal spine shows a mixed cystic and solid sacrococcygeal teratoma (straight arrow), which extends into the presacral space (arrowhead). Curved arrow = coccyx. (c) Type III. Sagittal T2-weighted image shows a mass with a cystic external component and extension of a solid portion into the fetal abdomen (white arrow). Arrowhead = umbilical cord insertion. A type IV mass would have no external component.
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Figure 3b. Classification of sacrococcygeal teratomas. (a) Type I. Coronal US image of a fetal spine shows a small, exophytic, cystic mass (straight white arrow) emanating from the coccyx (curved arrow). No internal component was identified. Black arrow = iliac crest. (b) Type II. Longitudinal US image of a lower fetal spine shows a mixed cystic and solid sacrococcygeal teratoma (straight arrow), which extends into the presacral space (arrowhead). Curved arrow = coccyx. (c) Type III. Sagittal T2-weighted image shows a mass with a cystic external component and extension of a solid portion into the fetal abdomen (white arrow). Arrowhead = umbilical cord insertion. A type IV mass would have no external component.
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Figure 3c. Classification of sacrococcygeal teratomas. (a) Type I. Coronal US image of a fetal spine shows a small, exophytic, cystic mass (straight white arrow) emanating from the coccyx (curved arrow). No internal component was identified. Black arrow = iliac crest. (b) Type II. Longitudinal US image of a lower fetal spine shows a mixed cystic and solid sacrococcygeal teratoma (straight arrow), which extends into the presacral space (arrowhead). Curved arrow = coccyx. (c) Type III. Sagittal T2-weighted image shows a mass with a cystic external component and extension of a solid portion into the fetal abdomen (white arrow). Arrowhead = umbilical cord insertion. A type IV mass would have no external component.
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Figure 4a. Type II sacrococcygeal teratoma. (a) Clinical photograph of an infant shows an obvious external mass. Preoperative work-up showed that the tumor extended into the presacral space. (b) Intraoperative photograph shows the internal component being resected.
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Figure 4b. Type II sacrococcygeal teratoma. (a) Clinical photograph of an infant shows an obvious external mass. Preoperative work-up showed that the tumor extended into the presacral space. (b) Intraoperative photograph shows the internal component being resected.
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Appropriate fetal classification of tumor extension is important for patient counseling, postnatal operative planning, and possible fetal intervention. It does not, however, have the same prognostic implications that it has in the pediatric population. There are far more compelling issues for fetal and perinatal survival, including composition (cyst vs solid), gestational age at diagnosis, vascularity, associated abnormalities, and complicating factors (hydrops, polyhydramnios, intratumoral hemorrhage, etc).
The sonographic appearance of a sacrococcygeal teratoma is typically that of a heterogeneous, mixed cystic and solid mass. The tumors may be purely cystic in 15% of cases (19). Interrogation with Doppler US is essential to evaluate tumor vascularity. The fetal spine should be meticulously evaluated for defects, as a myelomeningocele is the primary differential diagnosis. In addition, a sacrococcygeal teratoma may involve the spinal canal (6). The diagnosis of intrapelvic extension is important, however, not always possible with US because of poor soft-tissue contrast and shadowing from the pelvic bones. MR imaging has proved to be helpful in better delineating the internal component of a sacrococcygeal teratoma (6,9,13). MR imaging has the further advantage of enabling a truly solid tumor to be differentiated from a diffusely microcystic one, both of which may appear hyperechoic at US (6).
Sacrococcygeal teratomas can grow at a very rapid rate and reach enormous volumes, which can approach and even eclipse the volume of the fetus itself. Size alone, however, is not an independent variable for outcome (21). The most important prognostic indicator is the size of the solid component of the mass. Predominantly cystic tumors, even if large, have a much better prognosis, most likely because they have a lower prevalence of vascular steal and hemorrhage (15,21,22).
Solid tumors can be highly vascular. The metabolic demands of perfusing a large mass, coupled with arteriovenous shunting, can lead to high output cardiac failure and hydrops fetalis (15). Once a sacrococcygeal teratoma has been diagnosed, frequent sonographic surveillance is recommended to look for signs of impending fetal cardiovascular compromise. Evaluation should include measurements of tumor volume, amniotic fluid index, placental thickness, inferior vena cava diameter, and cardiothoracic ratio, as well as Doppler interrogation of the umbilical cord and ductus venosus (Fig 5) (19). If hydrops develops, the prognosis is uniformly poor (16,17,21,23).
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Figure 5a. Sacrococcygeal teratoma with developing cardiovascular failure. (a) US image of a fetal lower spine (Sp) shows a large complex mass with a substantial soft-tissue component (arrows). (b) Color Doppler US image demonstrates prominent feeding vessels (curved arrow) supplying the mass (straight arrow). (c) On a coronal US image of the fetal abdomen, the inferior vena cava (white arrow), compared with the aorta (black arrow, Ao), appears greatly dilated, a finding indicative of impending cardiovascular compromise. (d) Autopsy photograph shows obvious intratumoral hemorrhage within the teratoma.
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Figure 5b. Sacrococcygeal teratoma with developing cardiovascular failure. (a) US image of a fetal lower spine (Sp) shows a large complex mass with a substantial soft-tissue component (arrows). (b) Color Doppler US image demonstrates prominent feeding vessels (curved arrow) supplying the mass (straight arrow). (c) On a coronal US image of the fetal abdomen, the inferior vena cava (white arrow), compared with the aorta (black arrow, Ao), appears greatly dilated, a finding indicative of impending cardiovascular compromise. (d) Autopsy photograph shows obvious intratumoral hemorrhage within the teratoma.
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Figure 5c. Sacrococcygeal teratoma with developing cardiovascular failure. (a) US image of a fetal lower spine (Sp) shows a large complex mass with a substantial soft-tissue component (arrows). (b) Color Doppler US image demonstrates prominent feeding vessels (curved arrow) supplying the mass (straight arrow). (c) On a coronal US image of the fetal abdomen, the inferior vena cava (white arrow), compared with the aorta (black arrow, Ao), appears greatly dilated, a finding indicative of impending cardiovascular compromise. (d) Autopsy photograph shows obvious intratumoral hemorrhage within the teratoma.
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Figure 5d. Sacrococcygeal teratoma with developing cardiovascular failure. (a) US image of a fetal lower spine (Sp) shows a large complex mass with a substantial soft-tissue component (arrows). (b) Color Doppler US image demonstrates prominent feeding vessels (curved arrow) supplying the mass (straight arrow). (c) On a coronal US image of the fetal abdomen, the inferior vena cava (white arrow), compared with the aorta (black arrow, Ao), appears greatly dilated, a finding indicative of impending cardiovascular compromise. (d) Autopsy photograph shows obvious intratumoral hemorrhage within the teratoma.
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Polyhydramnios is frequently present and may cause premature labor and delivery. Therapeutic amnioreduction may be necessary for maternal comfort and reduction of uterine irritability (22). Oligohydramnios is much less common but may occur secondary to obstruction of the urinary tract (22). If oligohydramnios is severe, there may be associated pulmonary hypoplasia.
The most common associated anomalies seen with sacrococcygeal teratomas are genitourinary and include hydronephrosis, renal dysplasia, urethral atresia, urinary ascites, hydrocolpos, and undescended testes (22,24,25). Other reported anomalies are rectal atresia or stenosis, hip dislocation, and clubbed feet (22). Chromosomal abnormalities are not associated, and amniocentesis is not routinely performed (15).
Clinical management of pregnancies complicated by sacrococcygeal teratoma is often challenging. Significant obstetric complications occurred in 81% of patients in a recent study by Hedrick et al (22). Prenatal complications include polyhydramnios, oligohydramnios, preterm labor, preeclampsia, HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome, and hyperemesis (22). Another reported complication is the mirror syndrome, a potentially life-threatening condition with maternal fluid retention and hemodilution that resembles severe preeclampsia (26). The syndrome occurs in the setting of hydrops fetalis and manifests as progressive maternal edema "mirroring" that of the sick fetus. Immediate delivery is required to reverse this condition (19,21,22,26).
US-guided drainage of primarily cystic sacrococcygeal teratomas may reduce uterine irritability and prevent preterm delivery. It may also be performed immediately before delivery to prevent tumor rupture and to facilitate vaginal birth (Fig 6) (19,22). For solid tumors, there are few prenatal therapeutic options, and delivery should be considered as soon as possible after the lungs are sufficiently mature. Cesarean section is indicated for fetuses with large tumors to avoid dystocia, tumor hemorrhage, and avulsion.
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Figure 6a. In utero drainage of a large cystic sacrococcygeal teratoma. (a) US image of a cystic sacrococcygeal teratoma shows a needle being inserted into the sac (straight arrow) under US guidance. Curved arrow = tip of the spine. The contents were aspirated, which facilitated vaginal delivery. (b) Photograph of the infant obtained immediately after delivery shows the collapsed sacrococcygeal teratoma (arrow).
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Figure 6b. In utero drainage of a large cystic sacrococcygeal teratoma. (a) US image of a cystic sacrococcygeal teratoma shows a needle being inserted into the sac (straight arrow) under US guidance. Curved arrow = tip of the spine. The contents were aspirated, which facilitated vaginal delivery. (b) Photograph of the infant obtained immediately after delivery shows the collapsed sacrococcygeal teratoma (arrow).
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Outcome is almost universally fatal once placentomegaly and hydrops occur (21,22). Therefore, fetal surgery may be considered for a fetus with signs of impending high-output cardiac failure (22). Series are small, but results are promising with reversal of the spiral into cardiac failure; however, complications and preterm delivery are significant issues to overcome (21,22). Percutaneous radiofrequency ablation of sacrococcygeal teratomas has also been attempted. However, even when the technique has been successful in reversing cardiac failure, there has been substantial infant morbidity, largely related to complications of tumor necrosis (27,28).
Head and Neck Teratomas
The head and neck region is the next most common site of teratomas (1,2). Tumors may originate from the thyrocervical area, palate, or nasopharynx and are often large, bulky masses containing both cystic and solid elements. Calcifications are virtually diagnostic of a teratoma, but they are present in only about half of all cases and may not be obvious at US (15).
Cervical teratomas often involve the thyroid gland, although they are not thought to arise directly from thyroid tissue (4). They are unique compared with other teratomas in that there is no female predominance (15). These tumors are frequently large when first diagnosed and may extend posteriorly to the trapezius muscle, superiorly to the mastoid (displacing the ear), and inferiorly to the clavicle or even into the mediastinum (15). They may cause dramatic hyperextension of the fetal neck, resulting in malpresentation and dystocia (Fig 7) (15).
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Figure 7a. Cervical teratoma. (a) Coronal T2-weighted MR image shows a large mixed-signal-intensity mass (curved arrow) within the soft tissues of the fetal neck. The head (straight arrow) is being deviated to the side. (b) Clinical photograph of the infant shows the mass involving the anterior neck with hyperextension of the head.
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Figure 7b. Cervical teratoma. (a) Coronal T2-weighted MR image shows a large mixed-signal-intensity mass (curved arrow) within the soft tissues of the fetal neck. The head (straight arrow) is being deviated to the side. (b) Clinical photograph of the infant shows the mass involving the anterior neck with hyperextension of the head.
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Cystic hygroma is the primary differential diagnosis for a large neck mass. Sonographic features overlap, especially when the tumor is large, but cystic hygromas generally appear as septated fluid-filled collections with rare solid components. Cervical teratomas are located anteriorly, and cystic hygromas arise more posteriorly. The less common axillary lymphangioma can also achieve great size, is also multiseptated, but is more laterally located and involves the axilla and lateral chest wall. Other rare neck masses within the differential diagnosis include goiter, hemangioma, neuroblastoma, and soft-tissue tumors (29,30).
Teratomas associated with the mouth are referred to as epignathi and most commonly arise from the hard or soft palate (4). They typically fill the oral cavity and extend out through the mouth, appearing as an obvious fungating mass that may reach enormous proportions. They often contain both cystic and solid elements with areas of calcification (31) (Fig 8). In cases of epignathi, careful evaluation of the brain is essential, since transphenoidal intracranial extension can occur (4).
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Figure 8a. Epignathus. (a) Coronal US image obtained in the plane of the fetal nose (arrowhead) and lips shows a mass with cystic areas (curved arrow) and calcifications (straight arrow). (b) Three-dimensional reformatted image of the fetal head from an in utero CT examination shows the jaw held in an open position with obvious calcifications within the intraoral portion of the mass. (Reprinted, with permission, from reference 31.)
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Figure 8b. Epignathus. (a) Coronal US image obtained in the plane of the fetal nose (arrowhead) and lips shows a mass with cystic areas (curved arrow) and calcifications (straight arrow). (b) Three-dimensional reformatted image of the fetal head from an in utero CT examination shows the jaw held in an open position with obvious calcifications within the intraoral portion of the mass. (Reprinted, with permission, from reference 31.)
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The differential diagnosis of an epignathus is limited, but when the tumor is small, a frontal encephalocele should be considered. A cleft lip and palate may potentially mimic an anterior facial mass. Myoblastoma, a rare tumor found exclusively in females, has also been reported in the oral cavity (32).
Polyhydramnios is a common and important associated finding seen with cervical and oral teratomas and is the result of direct mass effect. Swallowing is compromised by occlusion of the mouth or compression of the esophagus (4,15). It is imperative that these patients be referred to a tertiary care facility for a carefully planned delivery. Reported mortality from lack of airway control is as high as 80%–100% (15,33,34). Even with maximal emergency procedures, hypoxia, acidosis, and anoxic brain injuries may occur.
A substantial improvement in survival can now be achieved by using the ex utero intrapartum treatment (EXIT) procedure (33,35,36). In the EXIT procedure, the fetus is partially delivered by cesarean section while the placenta and umbilical cord remain intact. The uteroplacental gas exchange is maintained, and the fetus remains hemodynamically stable for a considerable amount of time (mean times of 17.7–45 minutes reported) (33,35,36). The EXIT procedure provides a controlled environment in which to accomplish intubation, or if necessary tracheostomy, rather than a "crash" attempt at achieving an airway at birth (Fig 9). Although originallydeveloped for airway management after fetal surgery, the EXIT procedure has been shown to have great usefulness for treating fetuses with obstructing neck masses. Wagner and Harrison (33) reviewed 29 reported cases in which the EXIT procedure was used in the delivery of fetuses with neck masses (tumors and hygromas). An airway was established in 79% of cases, and the overall survival rate was 69%. In another study of 13 fetuses with obstructing neck masses, there was only one death (36). Appropriate planning clearly improves survival in these cases.
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Figure 9a. EXIT procedure. (a) US image of a fetal profile shows a complex cystic and solid mass (arrow) protruding from the mouth (arrowhead = lower jaw). (b, c) Intraoperative photographs show the intubation. The fetus was delivered via cesarean section and placed on the maternal abdomen. The placenta was left intact, and uteroplacental gas exchange was maintained while intubation was performed. (d) Photograph of the cut gross specimen shows the complex nature of the teratoma.
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Figure 9b. EXIT procedure. (a) US image of a fetal profile shows a complex cystic and solid mass (arrow) protruding from the mouth (arrowhead = lower jaw). (b, c) Intraoperative photographs show the intubation. The fetus was delivered via cesarean section and placed on the maternal abdomen. The placenta was left intact, and uteroplacental gas exchange was maintained while intubation was performed. (d) Photograph of the cut gross specimen shows the complex nature of the teratoma.
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Figure 9c. EXIT procedure. (a) US image of a fetal profile shows a complex cystic and solid mass (arrow) protruding from the mouth (arrowhead = lower jaw). (b, c) Intraoperative photographs show the intubation. The fetus was delivered via cesarean section and placed on the maternal abdomen. The placenta was left intact, and uteroplacental gas exchange was maintained while intubation was performed. (d) Photograph of the cut gross specimen shows the complex nature of the teratoma.
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Figure 9d. EXIT procedure. (a) US image of a fetal profile shows a complex cystic and solid mass (arrow) protruding from the mouth (arrowhead = lower jaw). (b, c) Intraoperative photographs show the intubation. The fetus was delivered via cesarean section and placed on the maternal abdomen. The placenta was left intact, and uteroplacental gas exchange was maintained while intubation was performed. (d) Photograph of the cut gross specimen shows the complex nature of the teratoma.
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Chest and Abdomen Teratomas
Teratomas involving the thorax and abdomen are relatively uncommon, collectively representing less than 10% of fetal teratomas (4). In the chest, the most likely sites of origin are the pericardium and mediastinum, with the lung being a very rare location (37–40). Teratomas occurring within the mediastinum most commonly originate anteriorly and may cross the midline. For large teratomas, the point of origin may be difficult to discern and they may mimic a lung mass. The presence of calcifications may help one differentiate mediastinal teratomas from the much more common lung masses, congenital cystic adenomatoid malformation and extralobar pulmonary sequestration (32).
Intrapericardial teratomas are invariably associated with pericardial effusions, which may be massive and mistaken for pleural effusions (Fig 10) (38,39). Large effusions may cause cardiactamponade with resulting cardiovascular compromise and fetal demise. Intrauterine pericardiocentesis has been successfully performed in this setting (39). The primary differential diagnosis is a rhabdomyoma, but they are generally smaller, intracardiac masses, whereas teratomas are external and may be massive.
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Figure 10a. Intrapericardial teratoma. (a) Color Doppler US image through a fetal chest shows a large echogenic mass (straight arrow) adjacent to the heart. Note the extensive surrounding pericardial effusion (curved arrows). (b) Coronal T2-weighted image shows a mixed-signal-intensity mass (straight arrow) adjacent to the heart (curved arrow). The mass is surrounded by high-signal-intensity pericardial fluid. No normal lung parenchyma is identified. (c) Autopsy photograph obtained with the pericardium intact shows a massive effusion, with the pericardial sac essentially filling the entire thoracic cavity. (d) Autopsy photograph obtained with the pericardium removed reveals the large teratoma (straight arrow) anterior to the heart (curved arrow).
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Figure 10b. Intrapericardial teratoma. (a) Color Doppler US image through a fetal chest shows a large echogenic mass (straight arrow) adjacent to the heart. Note the extensive surrounding pericardial effusion (curved arrows). (b) Coronal T2-weighted image shows a mixed-signal-intensity mass (straight arrow) adjacent to the heart (curved arrow). The mass is surrounded by high-signal-intensity pericardial fluid. No normal lung parenchyma is identified. (c) Autopsy photograph obtained with the pericardium intact shows a massive effusion, with the pericardial sac essentially filling the entire thoracic cavity. (d) Autopsy photograph obtained with the pericardium removed reveals the large teratoma (straight arrow) anterior to the heart (curved arrow).
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Figure 10c. Intrapericardial teratoma. (a) Color Doppler US image through a fetal chest shows a large echogenic mass (straight arrow) adjacent to the heart. Note the extensive surrounding pericardial effusion (curved arrows). (b) Coronal T2-weighted image shows a mixed-signal-intensity mass (straight arrow) adjacent to the heart (curved arrow). The mass is surrounded by high-signal-intensity pericardial fluid. No normal lung parenchyma is identified. (c) Autopsy photograph obtained with the pericardium intact shows a massive effusion, with the pericardial sac essentially filling the entire thoracic cavity. (d) Autopsy photograph obtained with the pericardium removed reveals the large teratoma (straight arrow) anterior to the heart (curved arrow).
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Figure 10d. Intrapericardial teratoma. (a) Color Doppler US image through a fetal chest shows a large echogenic mass (straight arrow) adjacent to the heart. Note the extensive surrounding pericardial effusion (curved arrows). (b) Coronal T2-weighted image shows a mixed-signal-intensity mass (straight arrow) adjacent to the heart (curved arrow). The mass is surrounded by high-signal-intensity pericardial fluid. No normal lung parenchyma is identified. (c) Autopsy photograph obtained with the pericardium intact shows a massive effusion, with the pericardial sac essentially filling the entire thoracic cavity. (d) Autopsy photograph obtained with the pericardium removed reveals the large teratoma (straight arrow) anterior to the heart (curved arrow).
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The retroperitoneum is an uncommon location for teratomas. However, tumors in this location tend to be highly organized and remarkably complex. Their unique morphology has led to the designation of fetus in fetu. A fetus in fetu is an encapsulated, pedunculated mass that exhibits morphologic development exceeding that usually seen in a teratoma. It has a "fetiform" appearance similar to that of an acardiac twin. By definition, the mass contains rudimentary vertebrae or notochord formation (Figs 11, 12) (4). Some authors argue that the requirement of vertebrae is too stringent and that any highly organized fetiform mass may be designated as a fetus in fetu (41).
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Figure 11a. Fetus in fetu. (a) Transverse US image through a fetal abdomen shows a markedly complex mass containing both cystic and solid components and areas of calcification (arrow). (b) Photograph of the gross specimen shows a highly differentiated mass with extremity development. Note the pedicle, which forms the vascular attachment (arrow).
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Figure 11b. Fetus in fetu. (a) Transverse US image through a fetal abdomen shows a markedly complex mass containing both cystic and solid components and areas of calcification (arrow). (b) Photograph of the gross specimen shows a highly differentiated mass with extremity development. Note the pedicle, which forms the vascular attachment (arrow).
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Figure 12a. Fetus in fetu. (a) Axial contrast material-enhanced CT image of an infant shows a large abdominal mass containing fat, fluid, and calcifications resembling vertebrae (arrow). (b) Photograph of the cut surface of the gross specimen shows a well-developed spine, which contained elements of a spinal cord. Other tissues identified were portions of a gastrointestinal tract, cartilage, bone, and bone marrow. All elements were histologically mature.
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Figure 12b. Fetus in fetu. (a) Axial contrast material-enhanced CT image of an infant shows a large abdominal mass containing fat, fluid, and calcifications resembling vertebrae (arrow). (b) Photograph of the cut surface of the gross specimen shows a well-developed spine, which contained elements of a spinal cord. Other tissues identified were portions of a gastrointestinal tract, cartilage, bone, and bone marrow. All elements were histologically mature.
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It has been proposed that fetus in fetu is the result of abnormal twinning and that a progression can be traced from normal twins, to conjoined twins, to fetus in fetu. Whether this entity represents a highly differentiated teratoma versus a parasitic twin remains controversial (4,41,42). In the latter theory, a fetus in fetu results from a monochorionic, diamniotic twin, which has become embedded into the host twin secondary to anastomoses between vitelline vessels. The amniotic membrane of the engulfed twin forms a surrounding capsule, with the fluid within the sac being equivalent to amniotic fluid. The vascular supply to the parasitic twin comes through the pedicle in a fashion reminiscent of the umbilical cord (Fig 11). The host vascular supply is generally from the superior mesenteric artery (vitelline artery derivative) or aorta (41). Others have disputed this theory and believe that fetus in fetu represents the most highly differentiated end of the teratoma continuum (4,42). Currently, the World Health Organization classifies fetus in fetu as a mature teratoma (4).
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Intracranial Tumors
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Primary central nervous system (CNS) tumors are a common group of neoplasms in the pediatric population, being second only to leukemia in frequency (43). The same, however, is not true for the fetus. CNS tumors represent only 10% of all antenatal tumors, ranking behind extracranial teratomas, neuroblastomas, and soft-tissue tumors (43,44).
In addition to relative frequency, other striking differences between fetal and pediatric CNS tumors include histologic characteristics, anatomic location, and prognosis. Intracranial teratoma, a relatively uncommon CNS tumor in children, is the most common fetal brain tumor, accounting for approximately half of all reported cases (5,43,44). They are followed in frequency by astrocytomas of varying grades, lipomas, choroid plexus papillomas, craniopharyngiomas, and primitive neuroectodermal tumors (5,43–45). With regard to anatomic distribution, the majority of fetal CNS tumors are supratentorial, whereas pediatric tumors are more commonly infratentorial (43,44). The third and most clinically significant difference between the two groups is prognosis. Patients with congenital brain tumors have a substantially worse outcome than patients with brain tumors who present later in childhood. The two notable exceptions are fetuses with lipomas and fetuses with choroid plexus papillomas, both of which fare far better than fetuses with other congenital brain tumors (5,45).
The most common prenatal US finding with intracranial tumors is macrocephaly, either as a direct result of the tumor or secondary to associated hydrocephalus. Hydrocephalus usually is caused by direct compressive effects with obstruction of the ventricular system, but it can arise from increased cerebrospinal fluid production from a choroid plexus tumor (43,46). Polyhydramnios, secondary to depressed swallowing from hypothalamic dysfunction, is a common complication. Either hydrocephalus or polyhydramnios may be present before the tumor is sonographically detectable (45).
Congenital brain tumors most commonly arise from the pineal gland, suprasellar area, or cerebral hemispheres; however, the point of origin often cannot be determined with imaging or even autopsy (43). These tumors may exhibit rapid growth over a very short period of time, causing gross distortion of cerebral architecture. The tumors most commonly manifest in the third trimester, sometimes in cases with a normal US scan as recently as 2 weeks prior (5). Associated congenital anomalies are not common (overall frequency, 14% of cases), except for lipomas, which have a strong association with agenesis of the corpus callosum (47,48). The most commonly reported associated malformation is a cleft lip or palate (43).
The imaging appearances of fetal brain tumors overlap considerably. Differentiation of individual tumor types is generally not possible, or even necessary, with imaging. The presence of a large mass disrupts normal neural development and portends a grave outcome, regardless of the histologic characteristics. Teratomas, the most common fetal brain tumors, are generally large, complex, mixed cystic and solid masses with or without foci of calcification (43). They typically arise in the midline, predominantly from the pineal gland, and involve the third ventricle (Fig 13) (45). They may exhibit very rapid growth and reach massive proportions (Fig 14). Most fetuses die in utero or shortly after birth with few long-term survivors (43).
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Figure 13a. Intracranial teratoma. (a) Transverse US image of a fetal brain shows a predominantly solid, echogenic midline mass (arrow), which is causing obstructive hydrocephalus. (b) Photograph of the gross specimen demonstrates a variegated, lobular mass (straight arrow) with marked thinning of the remaining cerebral tissue (curved arrow).
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Figure 13b. Intracranial teratoma. (a) Transverse US image of a fetal brain shows a predominantly solid, echogenic midline mass (arrow), which is causing obstructive hydrocephalus. (b) Photograph of the gross specimen demonstrates a variegated, lobular mass (straight arrow) with marked thinning of the remaining cerebral tissue (curved arrow).
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Figure 14a. Intracranial teratoma. (a) Transverse US image of a fetal brain shows a large, heterogeneous mass within the cranial vault (cursors) completely destroying normal anatomic landmarks. Measurements showed marked macrocephaly. (b) Postmortem coronal T1-weighted image demonstrates complete replacement of brain tissue by a complex mixed-signal-intensity mass. Immature teratoma (with primitive neural tissue, cartilage, bone, intestinal mucosa, smooth muscle, and hemorrhage) was identified at autopsy.
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Figure 14b. Intracranial teratoma. (a) Transverse US image of a fetal brain shows a large, heterogeneous mass within the cranial vault (cursors) completely destroying normal anatomic landmarks. Measurements showed marked macrocephaly. (b) Postmortem coronal T1-weighted image demonstrates complete replacement of brain tissue by a complex mixed-signal-intensity mass. Immature teratoma (with primitive neural tissue, cartilage, bone, intestinal mucosa, smooth muscle, and hemorrhage) was identified at autopsy.
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Astrocytomas follow teratomas in frequency (5,43–45). They are neuroglial tumors composed of astrocytes, varying from well to poorly differentiated. They are generally solid masses and most commonly are located in the cerebral hemispheres or thalamus, only rarely occurring below the tentorium cerebelli (43–45). The fetal manifestation of an astrocytoma is in marked contradistinction to the cerebellar pilocytic astrocytoma typically seen in the pediatric population.
Two other less common tumors, which may occur as large cerebral masses, are craniopharyngioma and primitive neuroectodermal tumor (PNET). Craniopharyngiomas arise from the Rathke pouch, an ectodermal diverticulum from the roof of the mouth, and form a suprasellar mass. They are heterogeneous, complex masses, which frequently calcify and are indistinguishable from teratomas at prenatal imaging (44). Primitive neuroectodermal tumors are a group of highly malignant, small cell tumors thought to derive from the neural crest (43). Although primitive neuroectodermal tumors are relatively common in the first year of life, they constitute only 3.4%–13.2% of fetal CNS tumors (43,45,48).
Choroid plexus papillomas are comparatively more common in fetuses than in children, accounting for approximately 5%–9% of congenital brain tumors in contrast to 1.6% of pediatric brain tumors (43,45,48). The most common site of occurrence is the lateral ventricle, but they can form anywhere there is choroid in the ventricular system. Rapid onset of hydrocephalus may occur from increased production of cerebrospinal fluid. On US images, choroid plexus papillomas are well-defined, lobular, hyperechoic, intraventricular masses (Figs 15, 16). They should not be confused with the much more common choroid plexus cyst.
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Figure 15a. Choroid plexus papilloma. (a, b) Transverse (a) and parasagittal (b) US images of a fetal head show a well-defined, lobular, hyperechoic mass (arrow) within the atrium of the right lateral ventricle. Hydrocephalus is also present. (c) Axial contrast-enhanced CT image of the brain demonstrates substantial enhancement of the mass (arrow). There is severe hydrocephalus with transependymal edema (arrowheads). (d) Photograph of the resected tumor shows the characteristic lobular contour.
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Figure 15b. Choroid plexus papilloma. (a, b) Transverse (a) and parasagittal (b) US images of a fetal head show a well-defined, lobular, hyperechoic mass (arrow) within the atrium of the right lateral ventricle. Hydrocephalus is also present. (c) Axial contrast-enhanced CT image of the brain demonstrates substantial enhancement of the mass (arrow). There is severe hydrocephalus with transependymal edema (arrowheads). (d) Photograph of the resected tumor shows the characteristic lobular contour.
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Figure 15c. Choroid plexus papilloma. (a, b) Transverse (a) and parasagittal (b) US images of a fetal head show a well-defined, lobular, hyperechoic mass (arrow) within the atrium of the right lateral ventricle. Hydrocephalus is also present. (c) Axial contrast-enhanced CT image of the brain demonstrates substantial enhancement of the mass (arrow). There is severe hydrocephalus with transependymal edema (arrowheads). (d) Photograph of the resected tumor shows the characteristic lobular contour.
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Abstract
LEARNING OBJECTIVES FOR TEST...
