Fetal Surgery for Sacrococcygeal Teratoma

Sacrococcygeal teratoma (SCT) is the most common congenital germ cell tumor, ^[1]  with an incidence of 1 in 35,000-40,000 live births ^[2] and a female predominance (3:1-4:1 ratio). ^{[2, 3]}  There is no clear geographic predominance, but a higher prevalence has been observed in Finland. ^[4]  The majority of cases are sporadic, with no definitive familial tendency.

In 11% of cases, patients also have associated congenital anomalies, often anorectal malformations. ^[5]  Rare cases of SCT can be associated with congenital anomalies representing the Currarino triad (sacral body defects, anorectal anomalies, presacral mass/SCT).

SCT arises from embryologically multipotent cells from the Hensen node, which is located in the coccyx. ^{[6, 7]}  Most SCTs are now diagnosed antenatally as a consequence of the widespread use of routine obstetric ultrasonography (US). ^[8] The majority are diagnosed in the second trimester via US, on which the earliest sign may be increased uterine size for gestational age. ^[9] Rarely, the diagnosis is made earlier; the earliest case described was diagnosed at 13 weeks' gestation. ^[10]  The differential diagnosis includes meningocele, myelomeningocele, neuroblastoma, perineal cyst, lymphangioma, lipoma, or enteric duplication cyst. ^[9]

The timing of diagnosis has implications for prognosis. Patients with postnatally diagnosed SCT typically do well after early surgical resection, and the main cause of the rare mortality in these patients is attributed to malignancy. Patients with antenatally diagnosed SCT, however, have a mortality in the range of 30-50%, ^{[11, 12, 13]} attributable to poor prognostic factors (eg, solid tumor morphology and increased tumor vascularity). Whereas some fetuses are born without complications, others can develop high-output cardiac failure, nonimmune hydrops fetalis (hydrops), and, ultimately, fetal demise.

This wide disease spectrum has prompted several fetal treatment centers to identify US predictors of survival for fetuses with SCT in an effort to helpdetermine which high-risk fetuses may benefit from fetal intervention. Poor prognostic factors on US imaging include signs of hydrops (eg, subcutaneous edema, ascites, or pleural effusion) or high-output cardiac failure (eg, inferior vena cava [IVC] dilation, absent/reversed ductus venosus flow, elevated combined ventricular cardiac output, or placentomegaly). ^{[14, 15, 16]}

The key to optimizing survival in these fetuses is intervention before the development of high-output cardiac failure, hydrops, and maternal mirror syndrome. Evaluation of tumor characteristics and echocardiographic findings aid in identifying fetuses at increased risk for these complications, who may derive the greatest benefit from fetal intervention. ^[17]

Pathophysiology

The vascular supply to an SCT commonly arises from the middle sacral artery, which can enlarge to the size of the common iliac artery and cause a vascular steal syndrome. ^[18] These large vascular tumors can lead to high-output cardiac failure as a consequence of arteriovenous shunting through the tumor, resulting in placentomegaly, hydrops, and, ultimately, fetal demise. ^[18]

Polyhydramnios is commonly seen due to increased fetal cardiac output, which often leads to preterm labor and premature rupture of membranes (PROM). Conversely, oligohydramnios can also occur if an intrapelvic portion of the tumor causes significant urinary obstruction. ^[3]

In severe cases, maternal mirror syndrome may develop, in which the mother manifests symptoms that mimic those of the hydropic fetus. These symptoms are similar to those of severe preeclampsia, such as hypertension, emesis, peripheral edema, pulmonary edema, and proteinuria. ^[12]

Fetal surgery is contraindicated after maternal mirror syndrome has developed. Mothers who may have maternal mirror syndrome must be monitored very closely, and delivery or pregnancy termination may be required for maternal safety.

Classification

SCTs are categorized according to the classification developed by the American Academy of Pediatrics, Surgical Section (AAPSS), as follows ^[19] :

• Type I - Primarily external (with or without a minimal internal/presacral component)
• Type II - Predominantly external, but also has a significant intrapelvic component
• Type III - Predominantly intrapelvic with abdominal extension, but also has a small external component
• Type IV - Entirely internal within the pelvis and abdomen

Whereas type I tumors, being primarily external to the fetus, are easily diagnosed antenatally and are amenable to fetal resection, type IV tumors can be difficult to diagnose and are not amenable to fetal resection. ^{[8, 20]} Thus, although the AAPSS classification describes surgical anatomy and identifies tumors that are amenable to fetal resection, it does not provide prognostic information, ^[3] nor does it identify fetuses who would benefit from fetal intervention.

Fetuses with SCT are considered for fetal resection or fetal intervention only in extreme cases and are evaluated on a case-by-case basis.

Small tumors without significant vascularity are unlikely to affect the fetus significantly. ^[3] These fetuses are unlikely to develop high-output cardiac failure or hydrops and can be monitored throughout gestation with serial US. Serial US is used to evaluate tumor size/growth, solid/cystic morphology, amniotic fluid volume, vascular flow, and fetal hydropic changes. ^{[21, 22]}

When there are signs of placentomegaly and hydrops after fetal lung maturity (usually after 32 weeks), the fetus is delivered on an emergency basis. Only fetuses of less than 26 weeks' gestation with signs of impending hydrops who have tumors amenable to surgical resection (AAPSS type I or type II) are considered for open fetal surgery (ie, tumor debulking). ^{[11, 20]} Fetuses of 26-30 week's gestation with impending hydrops can also be considered for fetal intervention, but the potential risks and benefits of open fetal surgery versus ex-utero intrapartum treatment (EXIT) to resection should be weighed. ^[23]

As with all invasive procedures, the risks and benefits of fetal intervention must be considered for each patient. However, considerations of the risk to and safety of the pregnant mother are unique to fetal surgery. Before fetal intervention is considered, a multidisciplinary team should counsel and evaluate each family. The evaluation should include the following ^{[20, 24]} :

• Detailed US to confirm the diagnosis, evaluate tumor characteristics, and detect any other anatomic abnormalities
• Fetal magnetic resonance imaging (MRI) for additional anatomic information (eg, spinal tumor extension, colonic displacement, or genitourinary obstruction) ^{[25, 26]}
• Fetal echocardiography to rule out congenital heart disease and to assess fetal cardiac function
• Amniocentesis for fetal karyotyping

In 2009, Wilson et al proposed the following criteria for surgical resection of SCT ^[27] :

• No maternal contraindications for fetal surgery (eg, presence of prohibitive medical or surgical comorbidities, body mass index [BMI] >36, or inability to tolerate anesthesia)
• Fetal gestational age of 20-30 weeks
• A favorable AAPSS stage and no additional congenital anomalies
• Impending hydrops (evidence of ascites, pleural effusion, subcutaneous edema, or pericardial effusion)
• Normal fetal karyotype
• Fetal cardiac output greater than 600-900 mL/kg/min (adjusted for gestational age)

Contraindications for fetal intervention for SCT include the following ^[27] :

• Significant placentomegaly (placental thickness at cord insertion >35-45 mm with gestational age < 30 wk)
• Maternal mirror syndrome
• Multiple gestation
• Chromosomal abnormality
• Other fetal anatomic abnormalities

Several institutions have reported outcomes with and without fetal intervention for antenatally diagnosed SCT. ^{[28, 29, 30, 31, 32]} Of patients with antenatally diagnosed SCT, 36-41% require fetal intervention. ^{[29, 30]}

Mortality due to SCT is mainly attributed to tumor morphology; small cystic SCTs rarely cause problems in utero. In contrast, rapid growth of large vascular tumors can lead to rupture and hemorrhage either in utero or during delivery; this is usually fatal. ^[20]

The overall survival rate of fetuses with antenatally diagnosed SCT is 47-83%, ^{[28, 30, 31]} but the survival rate after fetal surgery is 50-75%. ^{[28, 29, 30, 31]} It is important to note, however, that survival after fetal intervention should be compared with survival in the subgroup of patients with hydrops and no intervention, in whom the survival rate approaches 0%. ^{[33, 34]}

About 40-50% of survivors with antenatally diagnosed SCT have long-term morbidity, which may include obstructive uropathy or dissatisfaction with cosmetic outcomes. In addition, damage to the sacral nerves caused by the tumor itself or damage occurring during SCT resection can result in bowel/bladder incontinence, lower-extremity palsy, or sexual dysfunction at reproductive age. ^{[28, 32, 35, 36]}

Prognostic indicators

Placentomegaly and hydrops are harbingers of fetal demise in SCT. ^{[12, 37]} The presence of hydrops greatly increases the odds of fetal demise in fetuses with SCT (odds ratio, 21.0). ^[38]

A retrospective review of 17 fetuses with antenatally diagnosed SCT treated at the University of California, San Francisco (UCSF), between 1986 and 1998 evaluated the factors associated with hydrops. ^[17] There was a significant difference in tumor morphology (solid vs cystic) and vascularity in fetuses who developed hydrops as compared with those who did not. In addition, fetuses who developed hydrops were diagnosed at an earlier gestational age (19 vs 25 wk) and were delivered at an earlier gestational age (28 vs 38 wk). ^[17]

In this series, 12 fetuses developed hydrops, four of whom survived. ^[17] Of the four survivors, three underwent fetal intervention because they developed hydrops before viability, and one developed hydrops at 32 weeks' gestation and was delivered immediately. All fetuses who did not develop hydrops survived.

Similar retrospective reviews also identified cystic morphology as a positive prognostic factor, with solid morphology and tumors with high vascularity being associated with an increase in adverse outcomes. ^{[39, 40]}

These studies show that fetuses with predominantly solid and highly vascular tumors are at an increased risk for developing hydrops, which then increases the risk of fetal demise. These patients should undergo close follow-up throughout gestation with serial US and echocardiography and may be considered for fetal intervention upon signs of impending hydrops.

A retrospective review of 23 patients with antenatally diagnosed SCT who were evaluated at the Children’s Hospital of Philadelphia (CHOP) between 2003 and 2006 showed that SCTs with a growth rate exceeding 150 cm³/wk are associated with increased perinatal mortality. ^[27] A subsequent retrospective review from Zhejiang University (China) for the period between 2014 and 2021 found that a tumor growth rate higher than 48 cm³/wk was also associated with a poor prognosis (sensitivity, 100%; specificity, 78.3%; area under the curve [AUC], 0.880). ^[41]

In a study from UCSF that retrospectively reviewed 28 fetuses with antenatally diagnosed SCT between 1991 and 2005, solid tumor volume–to–head volume ratio (STV/HV) on US was identified as a predictor of poor outcomes. ^[42] All patients with an STV/HV lower than 1 survived, whereas 61% of fetuses with an STV/HV higher than 1 did not. ^[42]

In addition, the study determined that 97.3% of fetuses with an STV/HV higher than 1 were associated with one or more abnormal US findings, such as polyhydramnios, hepatomegaly, placentomegaly, cardiomegaly, ascites, pericardial effusion, or integumentary edema. ^[42] With serial US, increases in the STV/HV ratio can guide management of fetal SCT so that fetal intervention or early delivery can be performed before hydrops develops. ^[43]

In a study from the Fetal Center at Texas Children’s Hospital, tumor volume–to–fetal weight ratio (TFR) was a marker of poor outcome in 12 fetuses with SCT between 2004 and 2009, ^[33] With the use of MRI or US, tumor volume was determined via the prolate ellipsoid formula and fetal weight via the Hadlock formula. A TFR higher than 0.12 before 24 weeks' gestation predicted poor outcomes (fetal hydrops, demise, or neonatal death) with 100% sensitivity, 83% specificity, a negative predictive value of 100%, and a positive predictive value of 80%. ^[33]

Of the 12 fetuses with SCT in this series, 33% (4/12) developed hydrops. ^[33] All fetuses who developed hydrops had a TFR higher than 0.12 by 24 weeks' gestation, and three fetuses died. One patient underwent fetal intervention after hydrops developed and survived. Thus, TFR may be used to identify fetuses with SCT who are at risk for poor outcomes before 24 weeks' gestation and who may benefit from fetal intervention.

A TFR higher than 0.12 in combination with tumor morphology was further validated as a sonographic predictor of poor prognosis in subsequent retrospective studies from UCSF, ^[14] Zhejiang University (China), ^[41] and CHOP. ^[44] In addition, a TFR higher than 0.12 has been associated with increased maternal operative risk. ^[44]

In a review of 79 fetuses with antenatally diagnosed SCT at three fetal centers from 1986 to 2011, receiver operating characteristic (ROC) analysis revealed that a TFR higher than 0.12 before 24 weeks' gestation was predictive of a poor prognosis, as was solid tumor morphology and the presence of hydrops. ^[45] However, none of these factors were found to be independent predictors of a poor prognosis on multivariate analysis.

In a retrospective review of 28 pathology-confirmed isolated SCT patients evaluated with at least two documented US scans and followed through hospital discharge between 2005 and 2012, a faster SCT growth rate (calculated as the difference between tumor volume on a late-gestation sonogram and that on an early-gestation sonogram, divided by the difference in time) was associated with adverse outcomes (death, high-output cardiac failure, hydrops, and preterm delivery). ^[46]

SCT can create a low-resistance large arteriovenous shunt, which can progressively increase preload and afterload on the fetal heart, leading to volume overload, ventricular dilation, ventricular hypertrophy, and high-output cardiac failure. ^[47] A 10-year retrospective review of seven fetuses showed that the most important prognostic criteria for maternal and fetal complications due to antenatally diagnosed SCT included cardiomegaly, hydrops, and increased preload indices of the fetal venous system. ^[48] Fetuses with SCT and cardiomegaly exhibit increased odds for developing an adverse outcome (odds ratio 10.3). ^[38]

Studies on fetuses with SCT show that combined cardiac output increases dramatically before the development of hydrops. ^{[49, 50]}  Fetuses with combined cardiac output that exceeded 700-800 mL/kg/min died in utero. ^[47] Rychik et al analyzed the acute cardiovascular effects of fetal surgery in four patients with SCT and saw a significant decrease in combined cardiac output (690 ± 181 mL/kg/min vs 252 ± 82 mL/kg/min) after fetal resection of SCT. ^[51]

In a retrospective review of 11 fetuses with SCT, those with poor outcomes (hydrops, fetal demise, neonatal death) had a cardiothoracic ratio greater than 0.5, a combined ventricular output greater then 550 mL/kg/min, tricuspid or mitral valve regurgitation, or a mitral valve Z-score greater than 2. ^[15] Identifying these cardiovascular indicators as poor prognostic factors aids in the identification of patients at high risk for fetal demise and can prompt fetal surgical intervention before the development of hydrops.