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A sacrococcygeal teratoma / SCT is formed from multiple neoplastic tissues that lack organ specificity, that are foreign to the sacrococcygeal region, and that are derived from all three germ layers.
Sacrococcygeal teratoma / SCT is thought to arise from totipotent somatic cells originating in the primitive knot (Hensen node) or caudal cell mass and, by an unknown mechanism, escape the normal inductive influences of the surrounding normal cells.
Sacrococcygeal teratoma is the most common tumor in newborns, occurring in 1 in 35,000 to 40,000 live births.
The American Academy of Pediatrics Surgical Section (AAPSS) classification system groups these tumors according to the relative amount of pelvic or external tumor present. The importance of this classification system relates to the ease of detection and resection and, consequently, survival.
Type I tumors are completely external and easily identified on prenatal ultrasound examination or at birth, leading to early referral and resection with less morbidity.
In contrast, type IV tumors are completely internal and are usually recognized late, after they have undergone malignant transformation and become symptomatic.
Type II has intrapelvic extension of sacrococcygeal teratoma, and type III has intra-abdominal extension of sacrococcygeal teratoma. Fortunately, most SCTs are type I or II.
Although the postnatal mortality of sacrococcygeal teratoma / SCT is quite low and relates to development of malignant transformation, prenatal mortality from SCT is over 50% as a consequence of associated physiologic derangement or mass effect of the tumor. These effects are related to a vascular "steal" phenomenon, polyhydramnios-induced preterm labor, tumor rupture, and dystocia.
Depending on tumor size, rate of growth, ratio of cyst to solid composition, and probably the tissue components of the tumor, the metabolic requirements of sacrococcygeal teratoma vary dramatically. Furthermore, spontaneous internal or external hemorrhage of the sacrococcygeal teratoma / SCT may result from necrotic or cystic degeneration of the tumor as it outgrows its blood supply or because of minor trauma in utero.
The resulting fetal anemia may initiate or exacerbate the effects of the vascular steal. Both mechanisms may indeed lead to high output failure, placentomegaly and hydrops.
The diagnosis of sacrococcygeal teratoma / SCT is usually made by obstetric ultrasonography performed as a screening procedure or to assess uterine size too large for dates (polyhydramnios versus tumor enlargement).
Characteristic findings are of a caudal or intrapelvic mass, which can be routinely identified during the second trimester.
The sonographic appearance of a fetal sacrococcygeal teratoma / SCT may be cystic, solid, or mixed, and it may demonstrate irregular echogenic patterns secondary to areas of tumor necrosis, cystic degeneration, internal hemorrhage or calcification.
Other critical sonographic information includes the presence of abdominal or pelvic extension, evidence of bowel or urinary tract obstruction, assessment of the integrity of the fetal spine, and documentation of lower extremity function.
The major differential diagnosis includes myelomeningocele, meconium pseudocyst and obstructive uropathy. Sonographically detectable features that may exclude these other possibilities include the presence of normal kidneys, the absence of solid components and calcifications within the mass, the presence of spinal dysraphic features and the lack of a meconium appearance to the fluid contained within the cysts.
Echocardiographic and Doppler ultrasound measurements are essential following the diagnosis of a large sacrococcygeal teratoma / SCT. Echocardiographic features that should be monitored serially include inferior vena cava diameter, combined ventricular output, and descending aortic flow velocity.
In addition, Doppler ultrasonography is useful to detect reversal of diastolic blood flow in the umbilical arteries, which is indicative of "placental steal" by the sacrococcygeal teratoma / SCT.
Most importantly, signs of fetal hydrops should be sought, including pleural effusions or pericardial effusions, ascites, skin or scalp edema, cardiomegaly or placentomegaly.
Follow-up examinations in fetuses with hemodynamically significant sacrococcygeal teratoma / SCT demonstrate marked increases in combined ventricular output, descending aortic flow, and umbilical venous flow.
Total placental flow increases dramatically. However, the portion of total descending aortic flow directed toward the placenta decreases as a result of steal of the descending aortic blood flow by the enlarging sacrococcygeal teratoma / SCT.
At least weekly, if not twice weekly, sonography and echocardiography should be performed in sacrococcygeal teratoma / SCT to detect the development of high output failure as early as possible.
The published clinical experience with fetal surgery for sacrococcygeal teratoma / SCT is limited to a few series of patients treated at the University of California at San Francisco and The Children's Hospital of Philadelphia.
Review of the patients from these centers that were followed closely with serial ultrasonography and echocardiography reveals that the success of fetal intervention relies on early aggressive therapy before the onset of advanced physiologic or physical disturbance.
If fetal intervention is to be successful, then candidates must be selected with the earliest signs of high cardiac output physiology before the development of frank hydrops and severe placentomegaly.
If lung maturity has been reached, treatment should be focused on cesarean section delivery for postnatal resection of the tumor. Before lung maturity, fetal surgery is an option as long as overt hydrops has not developed and there is no evidence of preterm labor.
We recently reported our experience with 30 cases of prenatally diagnosed sacrococcygeal teratoma / SCT. The mean gestational age at diagnosis was 23 weeks with sacrococcygeal teratoma / SCT occurring in one fetus in 3 sets of twins. The outcomes in this series included terminations in 4, fetal deaths in 5, neonatal deaths in 7, and 14 survivors.
Of note, significant obstetrical complications occurred in 81% of the pregnancies including polyhydramnios (n=7), oligohydramnios (n=4), preterm labor (n=13), preeclampsia (n=4), gestational diabetes (n=1), HELLP syndrome (n= 1), and hyperemesis (n=1).
Fetal intervention in this series included cyst aspiration (n=6), amnioreduction (n=3), amnioinfusion (n=1), and open fetal surgical resection (n=4).
It is interesting that of the 15 solid sacrococcygeal teratomas at risk for the development of placental steal, placentomegally, and hydrops only 4 of the 15 met criteria for fetal surgery.
Of the 4 patients who underwent fetal surgery all were successfully debulked and delivered at a mean gestational age of 29 weeks' gestation (range 27.6 to 31.7 weeks').
The outcomes in these patients included a neonatal death due to closure of the ductus arteriosus in utero with secondary heart failure. A second child sustained in utero embolization following fetal resection with loss of the left kidney and multiple jejunal atresias. One child had chronic lung disease and another developed metastatic endodermal sinus tumor at 1 year of age.
In an effort to avoid the risk of open fetal surgery some groups have attempted to use laser or radiofrequency ablation or tumor embolization. The UCSF group reported a disappointing experience with radiofrequency ablation used in 4 prenatally diagnosed SCTs17.
Two fetuses died secondary to hemorrhage after a significant portion of the tumor mass was ablated. The other 2 patients delivered at 28 and 31 weeks' gestation respectively, with evidence of extensive perineal an gluteal necrosis.
Another case report of RFA described fetal demise on postoperative day 2. Ibahim et al, reported a newborn in whom radiofrequency ablation resulted in a large soft tissue defect, hypoplastic hip joint, and loss of sciatic nerve function.
The uncontrolled thermal effects of RFA may preclude its safe use to treat fetal sacrococcygeal teratoma / SCT given the close proximity of the tumor to the anorectal complex, vagina, urethra, sciatic nerves and hip joints.
As is the case with other fetal conditions which may cause hydrops and placentomegaly, sacrococcygeal teratoma / SCT can precipitate the maternal "mirror syndrome." This is an absolute contraindication to fetal surgery and every mother considering fetal surgery in the presence of a hydropic fetus and associated placentomegaly should be screened for maternal "mirror syndrome."
One of the earliest signs is the development in the mother of proteinuria and peripheral edema. A more ominous indication is the development of maternal hypertension.
In a situation similar to Congenital Cystic Adenomatoid Malformation / CCAM, close scrutiny must be given to the mother's postoperative fluid balance in sacrococcygeal teratoma as the high output failure in the fetus resolves and placental flow improves. The situation is especially tenuous in cases at risk for the maternal "mirror" syndrome.
Routine postoperative echocardiographic assessment should include measurement of ventricular diameters, combined ventricular output, descending aortic flow, umbilical vein flow, and vena cava diameter.
Consideration should be given to percutaneous umbilical blood sampling to check for fetal anemia and to perform fetal blood transfusion should evidence for high output failure persist.
With resolution of high output failure, decreased or resolved polyhydramnios, and control of preterm labor, a cesarean delivery should be planned as close to term as possible.
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