From the Guidelines
A bifid configuration of the 4th rib on a lung CT is typically a normal anatomical variant that requires no treatment or intervention. This finding occurs when the anterior end of a rib splits into two separate segments before connecting to the sternum, creating a Y-shaped or forked appearance. Bifid ribs most commonly affect the 3rd and 4th ribs and are generally considered benign incidental findings on chest imaging, as noted in various studies 1. They result from abnormal development during embryogenesis when the costal segment fails to fuse properly. While bifid ribs are usually asymptomatic and discovered incidentally on imaging performed for other reasons, they occasionally may cause localized pain or discomfort if the bifurcation creates pressure on surrounding tissues.
In the context of rib fractures, the classification system proposed by Sermonesi et al. 1 defines non-displaced, offset, displaced, and severely displaced fractures based on the degree of cross-sectional overlap. However, this classification system is more relevant to traumatic rib fractures rather than congenital anomalies like bifid ribs. The use of CT scans, as recommended by the ACR Appropriateness Criteria 1 and the WSES and CWIS position paper 1, is crucial for evaluating chest wall injuries and rib fractures but does not alter the management of bifid ribs, which are generally considered benign.
The key points to consider are:
- Bifid ribs are a normal anatomical variant
- They are usually asymptomatic and discovered incidentally
- They can occasionally cause localized pain or discomfort
- They are not associated with an increased risk of aortic injury or other complications, as noted in studies 1
- CT scans are useful for characterizing pathologic fractures and detecting fracture-related complications but are not necessary for the evaluation of bifid ribs unless symptoms are present.
Given the available evidence, no further evaluation or follow-up is necessary for an isolated bifid 4th rib unless it is causing symptoms. The focus should be on managing any symptoms that may arise and monitoring for any potential complications, although these are rare. The evidence from recent studies 1 emphasizes the importance of CT scans in evaluating chest wall injuries but does not support the routine use of CT scans for asymptomatic bifid ribs.
From the Research
Bifid Configuration of the 4th Rib on Lung CT
- A bifid rib is a congenital abnormality that can be detected on chest radiography and computed tomography (CT) scans, as seen in a case report of a 21-year-old woman with a bifid intrathoracic rib arising from the anterior-lateral portion of a depressed 4th rib 2.
- The prevalence of bifid rib is estimated to be around 0.6% in the healthy population, and it can be asymptomatic or associated with other pathological conditions 3.
- Bifid ribs can be classified into different types based on their morphology and developmental biology, and reconstruction 3D-CT can demonstrate complicated thoracic abnormalities in patients with atypical appearance of the rib on plain radiographs 4.
- Anatomical studies have shown that bifid ribs can have narrowed upper intercostal spaces and widened lower intercostal spaces, with intercostal muscles present in the bifid space 5.
- Chest ultrasound can also be used to diagnose bifid rib, especially in pediatric cases, and can provide useful information for differential diagnosis with other diseases such as chest wall tumors or costal fractures 6.
Diagnosis and Treatment
- Bifid ribs can be diagnosed on plain radiographs, but reconstruction 3D-CT can provide more detailed information about the anatomy of the bifid rib 4.
- In some cases, a watchful waiting treatment strategy may be adopted, especially if the bifid rib is asymptomatic 3.
- Knowledge of the anatomy and classification of bifid ribs is important for differential diagnosis with other diseases, and can help avoid unnecessary supplementary diagnostics 3, 5.