Purpose or Case Report: Undifferentiated embryonal sarcomas of the liver (UESL) and mesenchymal hamartomas are rare pediatric tumors. Mesenchymal hamartomas are benign and often seen in children under two years of age, while UESL are malignant tumors often seen in children six to ten years of age; however, age ranges are not universally true. There is an unclear relationship between these two tumors. Prior studies have hypothesized that mesenchymal hamartomas may evolve into UESL given reports of UESL within portions of mesenchymal hamartomas; however, few cases of this exist in the literature. There is a common relationship of 19q13.4 chromosomal alterations between these two lesions, the MHLB1 gene locus.

These tumors are difficult to differentiate on imaging alone, and biopsy is often required for diagnosis. Shared imaging features between these two tumors include large size, cystic with solid components, patchy enhancement, and occasional fluid-fluid levels. UESL occasionally present with poor margins and are fast growing (mesenchymal hamartomas are typically well-defined). These features are not universally consistent, which can make diagnosis difficult.

In this educational exhibit, we present three cases highlighting the clinical presentation, imaging features, treatments, and outcomes of patients with UESL and mesenchymal hamartomas. We showcase multi-modal imaging appearances of these lesions (ultrasound, CT, MRI, angiography) and their post-treatment changes. In particular, one case describes a 5-year-old female presenting with a hemorrhaging UESL which was subsequently resected. Follow-up imaging showed a new hepatic lesion concerning for recurrence. Histopathology of this new lesion showed findings consistent with mesenchymal hamartoma without evidence of UESL recurrence or other malignancy. Through these cases, we highlight similarities and differences between mesenchymal hamartomas and UESL, hoping to further explore a potential association between these two tumors.
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