Mesenchymal hamartomas of the chest wall in infancy: Radiologic and pathologic correlation

Mesenchymal hamartoma of the chest wall is a rare tumor with about 53 repor ted cases in the English literature. We reviewed six chest wall mesenchymal hamartomas in four patients, including two cases with multiple lesions, wi th specific focus on the radiologic and pathologic correlation. All cases o ccurred in neonates or infants with ages ranging from seven hours to seven months. They were diagnosed with plain chest radiographs (n=6), ultrasonogr aphy (n=2), chest CT scan (n=6), whole body bone scan (n=2) and MRI (n=3). All cases except a small one without cystic change showed the typical featu res of mesenchymal hamartoma radiographically and pathologically. Radiologi cally they were well-circumscribed masses with solid and cystic components with multiple fluid-fluid levels in association with single or multiple rib destruction or change. The CT scan showed the typical findings of chest wa ll homartoma, and the MR showed heterogeneous signal intensities of che mas s on T1- and T2-weighted images. The MR also revealed more concisely a seco ndary aneurysmal bone cyst formation with multiple fluid-fluid levels on th e T2-weighted image. Microscopically, they showed alternating areas of cart ilaginous islands and primitive appearing mesenchymal proliferation, which corresponded well with the solid component on the radiologic findings. The areas of bone formation and blood-tilled cystic spaces matched the calcifie d or ossified densities and the cystic components, respectively. A small ca se without cystic change showed peculiar radiological and pathological find ings resembling an osteochondroma. In conclusion, mesenchymal hamartoma of the chest wall in infancy is quite rare and sometimes can be misdiagnosed a s malignancy due to to he bone-destroying radiographic appearance and the h ighly cellular and mitotically active microscopic features, unless the radi ologists and pathologists are aware of the characteristic clinical, radiolo gical, and pathological findings. Imaging studies can usually make a correc t diagnosis with good correlation to the pathologic findings.