Teaching Case

An 18-year-old girl with a slow-growing mass in the right side of the chest, first noticed 1 year before.

A CT scan demonstrated a mass located between the fifth and sixth rib, originating from the 5th rib, with expansile growth and mineralisation.


A MRI study showed a lobulated mass closely related to the costal chondroid tissue (5th and 6th rib).
The mass had an intermediate to low signal intensity on T1-weighted images and inhomogeneous predominantly high signal intensity on T2-weighted images. Dimensions were 24 x 36 x 31 mm (AP x LR x CC). Administration of intravenous contrast demonstrated peripheral enhancement.

Chondromesenchymal hamartoma according to the latest WHO classification [4], also known as mesenchymal hamartoma of the chest wall or chest wall hamartoma [2], is an extremely rare, benign lesion with an uncertain pathogenesis. Chondromesenchymal hamartoma occurs mainly in early infancy and childhood [1]. It is usually solitary, but can be multifocal and even bilateral [2, 3, 5]. It arises most often on the right side and has a male-to-female ratio of 2:1 [3]. A chondromesenchymal hamartoma usually presents as a well-defined lesion arising within the medullary cavity or on the surface of a rib. Often contiguous ribs are affected [3].

Clinical manifestation depends on the size and specific location and ranges from a palpable or visible mass to severe respiratory distress due to compression of the lung [3].

On conventional chest studies, it appears as a mass arising from one or more adjoining ribs. The involved rib shows expansion, distortion and sometimes causes displacement of adjacent ribs. There is a variable degree of calcification [3]. In bigger lesions, secondary changes such as mediastinal displacement and scoliosis may be visible [3].
On CT it manifests as a bony lesion arising from the rib with osseous expansion and an associated extra-pleural soft-tissue mass with an inhomogeneous density and matrix mineralisation [7].
MRI usually shows heterogeneous signal on both T1- and T2-weighted sequences due to haemorrhage and cartilaginous components [7]. Haemorrhagic cystic regions with or without fluid-fluid levels due to secondary aneurysmal bone cyst formation are commonly visible [2].
This appearance on imaging is very similar to chondrosarcoma and often it is not possible to distinguish these two entities on imaging alone. The young age in combination with the location in the chest wall, however, favours the diagnosis of chondromesenchymal hamartoma.

A definitive diagnosis has to be verified by histopathological examination. Microscopically the lesions are composed of cartilage, fibroblastic regions and endochondral ossification. Focal stromal hypercellularity is often seen, but without atypia or abnormal mitotic activity [2]. Areas with blood-filled cystic spaces similar to aneurysmatic bone cysts are typically present [2, 4]. Different growth patterns are described in the literature varying from rapid growth, growth arrest to even reduction in size [6]. Surgical en-bloc resection is the treatment of first choice in symptomatic patients [2, 6].

Despite its sometimes alarming clinical, radiological and even histopathological appearance, chondromesenchymal hamartoma of the chest wall is a benign lesion, with an excellent prognosis after surgery.