Rare Fetal Sacral Appendage Studied


From the annual meeting of the American Institute of Ultrasound in Medicine

Major Finding: All seven fetuses with fetal sacral appendages had significant associated anomalies, and only one is surviving.

Data Source: A single-center study of seven fetuses with fetal sacral appendages evaluated over a 9-year period.

Disclosures: None was reported.

SAN DIEGO — A fetal sacral appendage carries a guarded prognosis, especially in the setting of associated anomalies, results from a single-center study demonstrated.

“Fetal sonography is still the primary mode for identifying the extension,” Lori J. Dobson said during the meeting. “It is important to measure fetal growth and look at the umbilical cord Doppler [scans], as well as to survey for additional anomalies. We did show that it is important to do a fetal MRI as it can help identify additional anomalies and help determine the position of the spinal cord conus.”

A fetal sacral appendage—also referred to as a fetal “tail”—is part of normal embryonic development, expected to resolve by the 8th week of gestation. While more than 30 published studies of prenatally diagnosed fetal sacral appendages have appeared in the medical literature, “the majority of cases are isolated, with no other structural anomalies reported,” said Ms. Dobson, a certified genetic counselor in the advanced fetal care center at Children's Hospital Boston. “And in most cases the appendage had resolved by the second trimester.”

She and her coinvestigators, some of whom performed fetal imaging, set out to describe the associated anomalies, etiology, and clinical outcome for a subset of the 3,641 patients evaluated at the hospital's advanced fetal care center over a 9-year period that ended in December 2009. Ms. Dobson reported that of the 3,641 patients, 7 fetuses (0.19%) had sacral appendages that ranged in size from 2.1 to 4.5 mm. The researchers assessed findings on fetal sonography and fetal MRI, results of genetic testing, and clinical outcomes.

“We noted that in all seven cases there was an extension of the coccyx causing a protrusion or a tenting of the skin,” she said. “Based on this, we propose the term sacrococcygeal extension to better describe the physical finding and its etiology. This is also a more patient-friendly term than fetal tail to use in counseling with parents.”

The average gestational age at diagnosis was 19 weeks. “Because we are a tertiary care referral center, it is not uncommon for us to only see patients in the second trimester or after,” she noted. “That may represent a bias in our sample. We did not have any cases that were diagnosed in the first or third trimester.”

All seven of the fetuses with sacral appendages had significant associated anomalies including severe growth restriction and neurologic, spinal, craniofacial, cardiac, renal, and musculoskeletal abnormalities. There were two cases of trisomy 13 and one case of Pfeiffer syndrome (craniosynostosis). “Most of our cases had multiple organ systems involved,” Ms. Dobson said.

She went on to report that three of the fetuses died in utero, two underwent elective termination, and one fetus with trisomy 13 was delivered at 36 weeks' gestation and died on the first day of life. The remaining case carried to term, and the infant is doing well at 5 months old, but does have a sacral appendage with a tethered spinal cord and an abnormal distal spine.

This sagittal view shows a fetal sacrococcygeal extension on ultrasound at 19 weeks', 4 days' gestation.

Source Courtesy Lori J. Dobson

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