Congenital hepatic mesenchymal hamartoma associated with mesenchymal stem villous hyperplasia of the placenta: case report

Marked placental hydrops is generally associated with hydatidiform mole. Diagnosis of hydatidiform mole requires both villous hydrops and trophoblast hyperplasia. This report describes four cases with massive hydrops of placental stem villi without associated trophoblast hyperplasia. All four had diploid DNA content by flow cytometry. Fetal omphalocele was present in three; and one had diagnostic Beckwith-Wiedemann syndrome (BWS). In two others, there were pathologic features suggestive of BWS. The fourth fetus had multiple anomalies by ultrasound; autopsy examination of the fragmented fetus failed to disclose additional pathology. The association of massive placental hydrops involving stem villi, fetal omphalocele, and diploid DNA content is unusual. These fetal and placental findings may suggest possible BWS in some cases and allow for antenatal diagnosis of affected fetuses, clinical evaluation of additional family members, and planning for neonatal care.

Here the first case in the literature of both mesenchymal hamartoma and malignant mesenchymoma occurring in a 6-year-old male child, at different times and at different sites in the liver, and also the possible malignant transformation of a mesenchymal hamartoma is reported. The tumor developed from a lesion in the right lobe that was overlooked initially during a left lateral segmentectomy at 18 months of age for a mesenchymal hamartoma. Malignant mesenchymoma is a rare and aggressive tumor. The origin of this tumor is not well understood. There has been no direct support to the hypothesis that malignant mesenchymoma may be the malignant counterpart of mesenchymal hamartoma. The authors provide clinical and histopathologic evidence in our case that suggests the possibility of malignant mesenchymoma arising from a mesenchymal hamartoma. This case emphasizes the need for complete removal of mesenchymal hamartoma and the need for long-term follow-up to detect multifocal lesion or malignant transformation.

The natural history of mesenchymal hamartoma of the liver is poorly understood. This case demonstrates the course of a biopsy-proven mesenchymal hamartoma using sequential computed tomography (CT) examinations. These CT scans show initial expansion of the lesion with subsequent involution. The spontaneous resolution in this patient suggests the possibility of conservative management of asymptomatic mesenchymal hamartomas. The case is presented, and the literature on mesenchymal hamartoma is reviewed.