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 and are rarely symptomatic, but they can also be associated with other malformations. Materials and methods: We reviewed imaging examinations performed over a period of 2 years (2014–2015), enabling us to identify isolated rib abnormalities in 6 adult patients. Results: The case series consisted in 3 cases with bilateral cervical ribs and 1 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 computed tomography (CT) scan. 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 tumoural, 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. Conclusions: It is important that radiologists are familiarised with the imaging features of rib abnormalities, since these anomalies can be misinterpreted as lesions with different implications. We are convinced that the developmental classification proposed in this paper can contribute to a better understanding of this pathology. (Folia Morphol 2018; 77, 2: 386–392