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Cervical rib
Cervical rib
Other names	Neck ribs
Specialty	Thoracic surgery

Cervical ribs are the ribs of the neck in many tetrapods. In most mammals, including humans, cervical ribs are not normally present as separate structures. They can, however, occur as a pathology. In humans, pathological cervical ribs are usually not of clinical concern, although they can cause a form of thoracic outlet syndrome.

Development

Like other ribs, the cervical ribs form by endochondral ossification.^[1]

Variation

The cervical ribs of sauropod dinosaurs were extended by ossified tendons,^[2] and could reach exceptional lengths; a cervical rib of Mamenchisaurus sinocanadorum was 4.2 metres (14 ft) long.^[3]

In birds, the cervical ribs are small and completely fused to the vertebrae.

In therian mammals, the cervical ribs fully fuse with the cervical vertebrae to form part of the transverse processes, except in rare pathological cases. In contrast, monotremes retain the plesiomorphic condition of having separate cervical ribs.^[4]

Pathological cervical ribs

A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2%^[6] to 0.5%^[7] (1 in 200 to 500) of the population.^[8] People may have a cervical rib on the right, left or both sides.^[9]^[10]

Most cases of cervical ribs are not clinically relevant and do not have symptoms;^[11]^[12] cervical ribs are generally discovered incidentally, most often during x-rays and CT scans.^[7]^[8]^[10] However, they vary widely in size and shape,^[7] and in rare cases, they may cause problems such as contributing to thoracic outlet syndrome,^[11] because of pressure on the nerves that may be caused by the presence of the rib.^[11]^[13]

A cervical rib represents a persistent ossification of the C7 lateral costal element.^[11]^[12] During early development, this ossified costal element typically becomes re-absorbed. Failure of this process results in a variably elongated transverse process or complete rib that can be anteriorly fused with the T1 first rib below.^[14]

Diagnosis

Bilateral, symmetric, full, ossified cervical ribs.

On imaging, cervical ribs can be distinguished because their transverse processes are directed inferolaterally, whereas those of the adjacent thoracic spine are directed anterolaterally.^[15]

Associated conditions

The presence of a cervical rib can cause a form of thoracic outlet syndrome due to compression of the lower trunk of the brachial plexus or subclavian artery.^[11] These structures become encroached upon by the cervical rib and scalene muscles.

Compression of the brachial plexus may be identified by weakness of the muscles in the hand, near the base of the thumb. Compression of the subclavian artery is often diagnosed by finding a positive Adson's sign on examination, where the radial pulse in the arm is lost during abduction and external rotation of the shoulder.^[11] A positive Adson's sign is non-specific for the presence of a cervical rib however, as many individuals without a cervical rib will have a positive test. Compression of the sympathetic chain may cause Horner's syndrome.

In other animals

Recent studies have also found a high percent of cervical ribs in woolly mammoths. It is believed that the decline in mammoth numbers may have forced inbreeding within the species which in turn had increased the number of mammoths being born with cervical ribs. Cervical ribs have been connected with leukaemia in human children, so it has given scientists new evidence to believe that the mammoth's extinction was attributed to the condition.^[16] They have also been interpreted as a sign of inbreeding depression in other mammals, such as Megaloceros.^[17]

References

^ Romer, Alfred Sherwood (1956). Osteology of the Reptiles.
^ Klein, Nicole; Christian, Andreas; Sander, P. Martin (2012-12-23). "Histology shows that elongated neck ribs in sauropod dinosaurs are ossified tendons". Biology Letters. 8 (6): 1032–1035. doi:10.1098/rsbl.2012.0778. eISSN 1744-957X. ISSN 1744-9561. PMC 3497149. PMID 23034173.
^ Moore, Andrew J.; Barrett, Paul M.; Upchurch, Paul; Liao, Chun-Chi; Ye, Yong; Hao, Baoqiao; Xu, Xing (2023-03-15). "Re-assessment of the Late Jurassic eusauropod Mamenchisaurus sinocanadorum Russell and Zheng, 1993, and the evolution of exceptionally long necks in mamenchisaurids". Journal of Systematic Palaeontology. 21 (1). Bibcode:2023JSPal..2171818M. doi:10.1080/14772019.2023.2171818. ISSN 1477-2019.
^ Weisbecker, Vera (2011). "Monotreme ossification sequences and the riddle of mammalian skeletal development". Evolution. 65 (5): 1323–1335. doi:10.1111/j.1558-5646.2011.01234.x. eISSN 1558-5646. ISSN 0014-3820.
^ Selim, Jocelyn. "Useless Body Parts".
^ Galis F (1999). "Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes, and cancer". J. Exp. Zool. 285 (1): 19–26. Bibcode:1999JEZ...285...19G. doi:10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z. PMID 10327647. Archived from the original on 2013-01-06.
^ ^a ^b ^c Terry Yochum; Lindsay Rowe (2005). Essentials of Skeletal Radiology (3 ed.). Lippencott & Williams.
^ ^a ^b Rochkind, Shimon; Zager, Eric (2012-01-01), Quiñones-Hinojosa, Alfredo (ed.), "Chapter 205 - Management of Thoracic Outlet Syndrome", Schmidek and Sweet Operative Neurosurgical Techniques (Sixth Edition), Philadelphia: W.B. Saunders, pp. 2339–2348, doi:10.1016/b978-1-4160-6839-6.10205-9, ISBN 978-1-4160-6839-6, retrieved 2020-10-23
^ Oner, Zulal; Oner, Serkan; Sahin, Necati Emre; Cay, Mahmut (26 January 2023). "Evaluation of congenital rib anomalies with multi-detector computed tomography in the Turkish population". Folia Morphologica. 83 (1): 182–191. doi:10.5603/FM.a2023.0006. PMID 36794687. S2CID 256899032.
^ ^a ^b Walden, Michael; et al. (2013). "Cervical ribs: identification on MRI and clinical relevance". Clinical Imaging. 37 (5): 938–941. doi:10.1016/j.clinimag.2013.01.005. PMID 23759210.
^ ^a ^b ^c ^d ^e ^f Giles, Lynton G. F. (2009-01-01), Giles, Lynton G. F. (ed.), "Case 67 - Cervical ribs", 100 Challenging Spinal Pain Syndrome Cases (Second Edition), Edinburgh: Churchill Livingstone, pp. 311–314, doi:10.1016/b978-0-443-06716-7.00067-0, ISBN 978-0-443-06716-7, retrieved 2020-10-23
^ ^a ^b Tani, Edneia M.; Skoog, Lambert (2008-01-01), Bibbo, Marluce; Wilbur, David (eds.), "CHAPTER 22 - Salivary Glands and Rare Head and Neck Lesions", Comprehensive Cytopathology (Third Edition), Edinburgh: W.B. Saunders, pp. 607–632, ISBN 978-1-4160-4208-2, retrieved 2020-10-23
^ Guttentag, Adam; Salwen, Julia (1999). "Keep Your Eyes on the Ribs: The Spectrum of Normal Variants and Diseases That Involve the Ribs". RadioGraphics. 19 (5): 1125–1142. doi:10.1148/radiographics.19.5.g99se011125. PMID 10489169.
^ E. McNally, B. Sandin & R. A. Wilkins (June 1990). "The ossification of the costal element of the seventh cervical vertebra with particular reference to cervical ribs". Journal of Anatomy. 170: 125–129. PMC 1257068. PMID 2123844.
^ Balan, Nisha Sharma, Anu (2008). Get through FRCR part 2B : rapid reporting of plain radiographs. London: Royal Society of Medicine. ISBN 978-1853157547.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ "Woolly Mammoths Suffered Major Birth Defects Before Extinction". IFLScience. 25 March 2014.
^ Cuxart-Erruz, Raimon; Van Dooren, Tom J. M.; van der Geer, Alexandra A. E.; Galis, Frietson (2024-09-24). "Increased incidences of cervical ribs in deer indicate extinction risk". Proceedings of the National Academy of Sciences. 121 (39): –2406670121. doi:10.1073/pnas.2406670121. PMC 11441530. PMID 39284067.