Spindle cell sarcomas are a rare and aggressive type of soft-tissue sarcoma. Although rhabdomyosarcomas are the most common childhood sarcoma, the spindle cell type is incredibly rare. A 25-year-old healthy G2P1001 female presents at 34 weeks gestational age with fetal growth restriction of a male fetus. Prenatal ultrasound showed a complex vascular mass exophytic to the distal spine, with a presumed diagnosis of sacrococcygeal teratoma (SCT). For further characterization, a fetal MRI was performed at 35 weeks gestation, which showed a solid appearing mass exophytic to the pelvis and involving the proximal thigh. Many features of the tumor were atypical for sacrococcygeal teratoma: the mass being more homogenous than expected, lacking cystic components that would normally been seen in a SCT, and involving the thigh but without definite involvement of the spine. It was also noted that the normal T1 meconium signal in the rectum was displaced posteriorly by the mass. At that time, an alternative differential diagnosis was suggested: sarcoma including fibrosarcoma or rhabdomyosarcoma, myofibroma, or less likely atypical sacrococcygeal teratoma. The baby was born via C-section at 37 weeks and 1 day gestation. A postnatal MRI showed the mass exophytic to the pelvis with some intrapelvic extension via the inguinal canal. Lack of spine involvement was confirmed. Signal characteristics of the tumor were similar to that of skeletal muscle, with a few focal areas of internal hemorrhage. The tumor had mass effect on multiple structures: deviating and tethering of the rectum to the right and stretching it inferiorly; displacing the anus posteriorly; uplifting the bladder; and abutting the base of the penis with no clear fat planes. Surgical resection was performed when the baby was 6 days old. Pathology evaluation revealed a sarcoma that was diffusely infiltrative with NTRK reactivity by immunohistochemistry. Molecular studies by next-generation sequencing reported TPM3-NTRK1 fusion in the tumor. Pathology was most suggestive of a spindle-cell sarcoma. It is important for the pediatric radiologist to be familiar with fetal soft tissue tumors to help facilitate family counseling and delivery planning. The radiologist should understand imaging features that may help distinguish more rare soft tissue tumors from sacrococcygeal teratomas. Although an exact diagnosis may not be possible prenatally, a multidisciplinary approach ensures the best possible patient outcomes. Read More

Meeting name: SPR 2025 Annual Meeting , 2025

Authors: Kazelka Maryam, Shao Lei, Mcgraw Marty, Neville Kucera Jennifer

Keywords: Sarcomas, Fetal Magnetic Resonance Imaging, Soft Tissue Sarcoma