Incidental imaging findings of congenital rib abnormalities - a case series and review of developmental concepts.

BACKGROUND Congenital rib abnormalities are found in approximately 2% of the general population. Usually, they occur in isolation, when they are rarely symptomatic, but they can also associate with other malformations. MATERIALS AND METHODS We reviewed imaging examinations performed over a period of two years (2014-2015), enabling us to identify isolated rib abnormalities in six adult patients. RESULTS The case series consisted in three cases with bilateral cervical ribs and one case each with bifid rib, costal fusion and rib pseudarthrosis. In all patients, the costal anomalies were discovered incidentally. All rib malformations were detected at thoracic radiography, except for the rib pseudarthrosis, which was identified at CT scan. DISCUSSION Differential diagnosis was made between cervical ribs and abnormalities of the C7 transverse process and of the first rib, while the other costal malformations were distinguished from tumoral, traumatic or inflammatory lesions of the chest wall, lung and pleura. Considering the existing knowledge on rib development, we suggest a classification of the most common types of rib malformations in three categories: (I) results of homeotic transformation, referring to numerical aberrations; (II) segmentation errors, including costal fusion and bridging; (III) anomalies of resegmentation, resulting in bifid ribs. CONCLUSION It is important that radiologists are familiarized with the imaging features of rib abnormalities, since these anomalies can be misinterpreted as lesions with different implications. We aim that the developmental classification proposed in this paper can contribute to a better understanding of this pathology.