An 18-week-old fetus with spinal abnormality

Clinical History

A primigravida underwent routine prenatal sonography at 18 weeks gestation. A fluid filled spinal mass was identified so she was referred to a tertiary care facility for further evaluation and management. A full-term female infant with a protruding sacral mass was finally born. Blood test showed Alphafetoprotein levels increased

Imaging Findings

Prenatal US showed a presacral heterogeneous cystic mass (Fig.1). Fetal Ultrafast T2-weighted MR images confirmed the presence of a presacral mass with two main components (one extra-pelvic and cystic and the other intra-pelvic and predominantly solid). Neither signs of spinal dysraphism nor intraspinal invasion were seen (Fig.2).
Postnatal Imaging started with a lateral radiograph of sacral spine (Fig.3) that showed a partially calcified mass occupying part of the neonatal pelvis without spinal bone involvement. Neonatal pelvic US (Fig. 4) identified a complex presacral cystic lesion. Before surgery, the patient underwent a pelvic MRI and thin-sliced T2-weighted sequence could determine the intra-pelvic extension and accurately delineate anatomical references of the lesion (Fig. 5 & 6).

Discussion

Fetal teratomas constitute the majority of fetal neoplasms. Extracranial teratomas are most commonly located in the sacrococcygeal area (SCT). Considered as benign tumours they are classified as either mature or immature but the location and size of the mass are far more important than the histologic grade for predicting outcome [1, 2].
Prenatal imaging is critical for counselling the parents and planning delivery and postnatal surgery [3, 4]. SCT are normally detected in fetal US but the evaluation of the intrapelvic extension of the tumour because of acoustic shadowing of pelvic bones may be difficult. Therefore, fetal MRI thanks to its better tissue discrimination can improve prenatal assessment of these patients and offers precise information about intrapelvic or intraabdominal extent and the content of the tumour; an important feature associated with high morbility in neonates. Sonographic features of SCT depend upon tumoural maturity and size. There are tumours, which are as solid and big as the fetus itself. These appear as huge echogenic protuding masses, with important vascular components that can lead to massive bleeding or fetal heart failure, and consequently, fetal hydrops and even fetal demise. In contrast, SCT may appear as a cystic intrapelvic tumour that does not cause problems antenatally, but is diagnosed only after delivery.

According to the American Academy of Pediatrics Surgery, SCT can be classified into four types based on the amount of mass present externally versus internally: type I, the tumour developed only outside the fetus; type II, extrafetal and intrapelvic presacral extent; type III, extrafetal and abdominopelvic extent; type IV, the tumour developing completely in the fetal pelvis [4].

Differential diagnosis of congenital sacrococcygeal masses includes other entities like meningomyelocele and less commonly neuroblastoma or lymphangioma [5].

Postnatal imaging should start with pelvic and lumbo-sacral spine radiography to study bone deformities. US can depict cystic presacral masses and evaluate their vascularization with Doppler technique. Presurgical planning may require a neonatal abdomen and pelvic MRI to see the tumour extent [6].

Surgery is the unique therapeutical option for SCT and the prognosis is usually good.

In prenatal imaging, presacral masses must be thoroughly evaluated to establish an accurate diagnosis. SCT is the most frequent fetal tumour in this area. Postnatal imaging will be necessary for surgical planning.

Differential Diagnosis List

Final Diagnosis

Sacrococcygeal teratoma type II

URL:	https://www.eurorad.org/case/10570
DOI:	10.1594/EURORAD/CASE.10570
ISSN:	1563-4086