Counting ribs on CT by assessing costal attachments to the proximal xiphoid: is this method accurate?

OBJECTIVES

To evaluate the usefulness of the method of counting ribs by assessing anatomic variations of the attachments of costal cartilages to the proximal xiphoid.

MATERIALS AND

METHODS

From January to September 2005, 224 subjects (136 men, 88 women, age 13 to 89 years, mean age 55 years) underwent computed tomography examination of the chest. Axial images of the chest were obtained on a 16-slice multidetector computed tomography. Counting ribs was performed by using the medial clavicle as an anatomic landmark to identify the first costal cartilage. We analyzed variety and incidence of the attachment patterns of costal cartilages to the proximal xiphoid.

RESULT: Out of the 224 patients, the last costal attachments to the proximal xiphoid were the sixth costal cartilages bilaterally for 2 (0.9%) subjects, one 6th and one 7th for 4 (1.8%) subjects, bilateral seventh for 191 (85.3%) subjects, one 7th and one 8th for 15 (6.7%) subjects, and bilateral eighth for 12 (5.4%) subjects.

CONCLUSIONS

The method of counting ribs from the proximal xiphoid is inaccurate because the sixth, seventh, and eighth costal cartilages may each attach to the proximal xiphoid.