Fetal Sacrococcygeal Teratoma and the Risk of High-Output Cardiac Failure

Sacrococcygeal teratoma is one of the more dramatic diagnoses a perinatal team can encounter on a routine morphology scan. The mass arising from the caudal end of the fetus can grow rapidly, distort the pelvis, and in its most aggressive vascular forms behave like a parasitic vascular bed that steals a sizeable fraction of the combined fetal cardiac output. The clinical community that gathered around the Federation of Asian and Oceania Perinatal Societies, including Australian perinatologists contributing through the official congress portal, has long treated SCT as a high-priority teaching subject because it sits at the intersection of diagnostic imaging, fetal physiology, and ethically complex intervention.

In Australian practice, most affected pregnancies are picked up between 18 and 22 weeks during the standard mid-trimester scan that Medicare covers under obstetric ultrasound rebates. The detection rate is high in tertiary fetal medicine units in Brisbane, Melbourne, and Sydney, where sonographers are trained to scrutinise the sacral region, but the condition still catches regional teams by surprise when a patient travels from a remote area such as the Pilbara or western Queensland for what was meant to be a routine anatomy review.

When a teratoma is vascular enough to behave as a low-resistance arteriovenous shunt, the fetal heart has to push a much larger circulating volume to meet both its own metabolic needs and the demands of the tumour. The result is a high-output state that can tip into frank cardiac failure, with hydrops, cardiomegaly, and eventually stillbirth if nothing is done. Understanding how that transition happens, and what can be offered before it does, is the focus of contemporary perinatal care in this condition.

How a Sacrococcygeal Teratoma Overwhelms the Fetal Heart

The tumour itself is a germ cell tumour containing derivatives of all three embryonic layers, but its clinical behaviour is dictated less by histology and more by vascularity. Predominantly solid, richly perfused lesions act as a parallel circulation that bypasses the high-resistance placental circuit. Blood rushes through the tumour, returns to the heart through a dilated venous system, and forces the right ventricle to handle a chronic volume load.

In the early second trimester the fetal myocardium is still plastic and can compensate through hypertrophy and increased stroke volume. The tipping point usually arrives when the tumour-to-fetal-weight ratio climbs above a threshold often cited around 0.12 before 24 weeks. At that point the heart begins to fail, evidenced on ultrasound by increasing cardiothoracic ratio, reversed flow in the ductus venosus, and eventually tricuspid regurgitation. Australian sonographers describe these findings in shorthand during a busy clinic arvo, but the implications are anything but casual.

Placental support also degrades as the high-output state pulls blood away from the chorionic villi. A starved placenta compounds the hypoxic stress on the fetus and accelerates the descent into hydrops. This is why teams monitor the middle cerebral artery peak systolic velocity as well, since fetal anaemia from intratumoural haemorrhage can mimic or worsen the cardiac picture.

Antenatal Imaging and Surveillance Protocols

Once an SCT is identified, Australian fetal medicine services shift into a structured surveillance rhythm. Most quaternary centres, including the Royal Brisbane and Women's Hospital and the Mercy Hospital for Women in Melbourne, schedule fortnightly growth and Doppler studies, tightening to weekly if the tumour is large, predominantly solid, or showing signs of accelerated growth. The aim is to characterise the lesion and catch the cardiac warning signs early.

The Altman classification, which sorts SCTs into four types based on the proportion of internal versus external components, remains the standard way to communicate the anatomy between sonographers, surgeons, and neonatologists. Type I lesions are mostly external and usually have a better prognosis, while Type III and Type IV lesions extend deep into the pelvis and can complicate both delivery and postnatal resection. The classification helps Australian teams triage referral urgency, especially when a family is being flown in from a regional centre.

Cardiac surveillance goes beyond simple biometry. Cardiac Z-scores, the myocardial performance index, and the presence of pericardial effusion are tracked alongside conventional Doppler indices. When cardiomegaly and reversed ductus venosus flow coexist, the team starts to discuss whether the fetus is a candidate for in-utero therapy or whether delivery and stabilisation are the safer path. In centres linked through the Perinatal Society of Australia and New Zealand network, these discussions often happen on multidisciplinary video conferences that span the country.

Fetal Intervention: What Is Offered and What the Evidence Shows

The most aggressive intervention for early severe SCT is open fetal surgery with resection of the tumour while the fetus remains on placental support. This approach, pioneered at a handful of centres internationally, has been used selectively in Australia when a fetus meets strict criteria: predominantly external lesion, signs of high-output failure before 28 weeks, and no associated genetic or structural anomalies that would preclude meaningful survival. The technical demands are extraordinary, and few Australian cases have been reported, so referral pathways typically involve collaboration with overseas units.

Minimally invasive options are more widely discussed in Australian counselling rooms. Interstitial laser ablation of the tumour's feeding vessels, radiofrequency ablation, and sclerotherapy have all been described as ways to reduce tumour vascularity and unload the fetal heart. The evidence base is modest, mostly comprising small case series, and the conversation with parents is honest about the trade-offs: a chance of stabilising the fetal circulation balanced against risks of preterm labour, fetal injury, or failure to reverse hydrops.

For many Australian families, the most realistic decision is between expectant management with intensive surveillance and elective delivery once the fetus reaches a viable gestational age, balanced against the risk of in-utero demise. When families travel from regional centres, the social and logistical realities matter as much as the physiology. A couple from Broome might need to relocate to Perth for weeks, and a Torres Strait family may need to negotiate cultural considerations around intensive medical intervention. Good perinatology practice here means acknowledging that the medical decision sits inside a much wider life context.

Delivery Planning and Immediate Neonatal Care

Mode of delivery is dictated by tumour size and composition. Small, predominantly external lesions can usually be delivered vaginally without complication, although the obstetric team should be prepared for dystocia if the mass exceeds the pelvic inlet. Large, vascular, or predominantly internal tumours are usually delivered by classical caesarean section to avoid tumour rupture and torrential haemorrhage. In a country with vast distances, the delivery is scheduled at a centre with both high-level neonatal intensive care and paediatric surgical capability, and the in-utero transfer is arranged through the relevant state retrieval service.

At birth, the priorities are securing the airway, supporting the often-still-unstable circulation, and obtaining urgent imaging to define the tumour's feeding vessels. Many neonates arrive in a low-output state despite the in-utero high-output picture, because the abrupt removal of placental support exposes an exhausted myocardium. Neonatologists in Australia are practised at this transition, having cared for similar physiology in twin-twin transfusion survivors and in infants with large hepatic haemangiomas.

Postnatal resection is the definitive treatment, usually performed within the first 24 to 48 hours for high-risk lesions. The coccyx must be removed completely to minimise recurrence, and the procedure is best undertaken by a paediatric surgical team with specific experience in teratoma resection. Long operating times, significant blood loss, and the need for pelvic reconstruction are all expected challenges, and parents are counselled early that the neonatal stay may extend for weeks rather than days.

Long-Term Outcomes and Family Follow-Up

Survival for prenatally diagnosed SCT has improved substantially over the past two decades, largely because of better imaging, structured surveillance, and timely delivery. Most Australian survivors face the real risk of long-term bladder and bowel dysfunction from pelvic nerve injury, and a smaller proportion experience lower limb weakness or scoliosis related to the surgical field. These functional outcomes drive the structure of follow-up clinics, which combine paediatric surgery, urology, and developmental paediatrics.

Recurrence is uncommon when the coccyx is removed completely, but surveillance ultrasound of the surgical bed continues for several years, often coordinated through state-wide paediatric oncology late-effects services. Mature teratomas with frankly malignant elements require oncological input, although most neonatal SCTs are histologically mature or immature rather than frankly malignant.

For families, the psychological footprint of the pregnancy and neonatal period is significant. Many Australian parents describe the months after discharge as a strange combination of relief and lingering hypervigilance, particularly when the antenatal course was marked by threatened hydrops or emergency delivery. Connecting these families with peer support groups and with psychologists familiar with high-risk perinatal journeys is now considered a routine part of comprehensive care, not an optional extra.

The table below summarises how the Altman types of sacrococcygeal teratoma tend to behave clinically and what that means for management planning.

For clinicians preparing presentations, posters, or teaching sessions on this topic, the archived FAOPS 2020 program remains a useful record of the international conversation around fetal therapy and high-risk perinatal management, even though the live congress in Tokyo was disrupted by pandemic-related travel restrictions. Australian perinatologists, neonatologists, and paediatric surgeons continue to share cases, refine thresholds for intervention, and build the evidence base that will, in time, make decisions for families facing this diagnosis a little clearer and a little kinder.