INTRODUCTION

The cervical rib (CR) is a skeletal anomaly that arises from the seventh cervical vertebra and is rarely seen in the community. Radiograph images indicate that the prevalence of cervical ribs is below 1 % in Turkish population; however, studies have found its occurrence to vary significantly from 0.58 % to 6.2 % depending on different population (^{Erken et al., 2002}; Spadlinski et al., 2016; ^{Henry et al., 2018}). The prevalence of the CR has found to be 3 % in anatolian population (Turkey) (^{Gulekon et al., 1999}). In this single study from our country, the higher occurrence was demonstrated in women (2.17 %) than men (0.83 %). Incomplete CRs were found in 2.24 % of cases. The incidence of complete CRs was found in 0.76 % of cases. However, a clarifying description of the so-called complete CR form has not been found in the literature. It is rarely associated with thoracic outlet syndrome (TOS), although it usually has an asymptomatic course, which is usually incidentally detected on routine chest radiographs (^{Makhoul & Machleder, 1992}; ^{Davidovic et al., 2003}). But on the contrary, in many patients, isolated rib anomalies can be easily missed on standard chest radiographs (^{Aignatoaei et al., 2018}). Surgical intervention is not needed since it often has an asymptomatic course (^{Davies et al., 1991}). It has a variable length that can be longer than 1 cm and can extend up to the thoracic outlet (^{Guttentag & Salwen, 1999}).

There is a wide spectrum of morphologic variants of rib abnormalities and unfortunately, in most instances, the boundary between malformation and anatomical variation remains unclear (Erken et al.; Spadlinski et al.; Aignatoaei et al.). In the presence of CR and the increase in the size of the cervical rib, the boundaries of the inter scalene triangle can be further constricted and result in neurovascular compression and TOS (Henry et al.). Some cases can often have arterial symptoms, albeit the reported high frequency of neurogenic symptoms (Spadlinski et al.; Henry et al.).

Isolated rib malformations are considered by some authors "normal variants" and mainly include supernumerary ribs (cervical, lumbar), bifid ribs, rib synostosis and aplasia of the ribs (Henry et al.). Cervical ribs may also present as a mimic palpable mass in the supraclavicular fossa or may be presented as pulsation due to the displacement of the subclavian artery (Spadlinski et al.).

The CR was first described and classified into four subgroups by Gruber in 1869 (^{Adson & Coffey, 1927}; ^{Abdel Ghany et al., 2017}). In the 1st type, there is the only extension in the transverse process. In the 2nd type, the transverse protrusion is quite long enough to touch the 1st rib. In the 3rd type, there is a CR, which is independent of the transverse process, but articulated with it, where the tip of the cervical rib is connected to the 1st rib with fibrous cartilage. The fourth type is quite rare, where is a complete CR that fuses fully to the lateral superior of the first rib (^{Povlsen et al., 2014}). Some authors have further simplified this classification by defining the terms "partial CR" and "complete CR" (^{Vemuri et al., 2017}). The complete CRs are actually type 4. Cervical rib is also known as “Eve’s rib” (^{Jeung et al., 1999}).

The case described in this study is a very good example of complete type 4 CR. However, the anatomical appearance of a real rib attached to the cervical vertebra has produced a need for a more definitive definition. The literature review did not reveal a similar case presented with 3D images.

CASE REPORT

A 23-year-old female patient presented with a mass described as slowly growing since her childhood in the supraclavicular region on the right side of the neck. She complained of pain, numbness, weakness, and difficulty in lifting his right arm, which has increased gradually over in the last 6 months. Physical examination revealed findings of thoracic outlet syndrome. X-ray and CT examinations showed a large cervical rib in the size of a real thoracic rib, which articulated with the transverse process of the 7th cervical vertebra, originated from the vertebral body and formed a true arc and fused to the first rib. The patient's clinical complaints have increased steadily over the past 2 years. The patient reported complaints of difficulty and weakness in lifting the arm beginning from the employment status. The electrophysiological study of the brachial plexus did not reveal any positive findings. However, the Adson test showed a weakening of radial pulse even in arm abduction. An incision of 3 to 4 cm was made in the closest position of the CR to the skin (supraclavicular approach) and the cervical rib was first dissected tracing up to the junction with 7th cervical vertebra and resected. Then, it was carefully cut and separated using a high-speed drill from the first rib, where it had extended downward to and fused (Fig. 1). The complaints of the patient were completely resolved after surgery. Pre-operative and post-operative X-ray and 3D-CT images are shown in Figure 2.

Fig. 1 A. Surgical position for supra-clavicular approach. B. Aspect to cervical rib surface during dissection. 

Fig. 2 A and B. Antero-posterior X-ray images. C, D, E, F. Three-Dimensional (3D) Computed tomography images. Expansion of thoracic outlet is observed after resection of the great cervical rib on d and f section. It is also observed that the whole of the cervical rib is the bone like a real rib. 

DISCUSSION

The CR is believed to be originated from an embryonic developmental defect. At the end of the fourth week of embryogenesis, the cells of the sclerotome convert intomesenchymal cells and then into ribs. Hox genes are responsible for patterning of the axial skeleton, and mutations within them probably are implicated in the development of cervical ribs (^{Deschamps & van Nes, 2005}; ^{Mallo et al., 2009}; ^{Bots et al., 2011}). It has been hypothesized that abnormality in the expression of Hox genes could influence oncogenesis with previous studies. Children with Germ cell tumors and astrocytoma were diagnosed with a higher rate of such cervical anomalies as cervical ribs (^{Merks et al., 2005}). Another gene responsible for skeletal formation and growth is growth differentiation factor 11 (GDF11) (^{Li et al., 2010}). Destruction of GDF11 function causes abnormal patterning of the anterior/posterior axial skeleton (Li et al.). Although GDF11 propeptide was shown to inhibit GDF11 activity in vitro, its effect on GDF11 function in in vivo models has not been reported (Li et al.). Especially with this work in considered that transgenic overexpression of GDF11 propeptide under the control of a1 type 1 collagen promoter resulted in the transformation of C7 to a thoracic vertebra (Li et al.). In this study, we wanted to emphasize where the transformation can last.

The presence of cervical ribs is usually asymptomatic (90 % of patients) and does not need to their removal (Spadlinski et al.). In addition, the emergence of neurological and vascular clinical manifestations is not always related to the size of the cervical rib. The anatomical size and position must be well understood in order to better understand the underlying cause or manifestation of clinical findings. CRs are usually reported to cause only unilateral complaints, albeit reported bilaterally in almost all cases (Adson & Coffey; ^{Ferrante, 2012}; Povlsen et al.; Vemuri et al.). The presented case had complaints only in his right arm, who had type 1 cervical rib on the left side (Fig. 2).

In the normal anatomy, the subclavian artery and brachial plexus travel through space between the anterior and medial scalene muscles toward the arm. This narrow space is further narrowed by the inclusion of a CR. The subclavian artery and brachial plexus are subjected to further compression in the thoracic outlet, mainly due to the convergence of the clavicle to this area, secondary to the abduction of the arm (Abdel Ghany et al.). Clinical manifestations occur at a young age in patients with this type of CR. Elevation and upward pressure of the brachial plexus and pressure on the subclavian artery lead to neurological and vascular symptoms, respectively, or both. Or they can only be presented with a growing mass in the neck region (^{Buyukkaya et al., 2015}). There can be the pain in the forearm and hand, paresthesia, loss of strength in the muscles of the region, and difficulty in finger movements (Adson & Coffey; Ferrante; ^{Chang et al., 2013}; ChweiChin Chuang et al., 2016). Pain and numbness is more common in the ulnar nerve region of the hand. Neurological complaints may be resolved by changing the position of the arm. In the present case, there were both neurological findings and arterial findings where there is a reduction in radial pulse with positional changes.

Many authors have reported that follow-up is sufficient for asymptomatic cases. However, it has been reported that surgical treatment is the most appropriate treatment method for a CR causing such severe clinical complaints (Ferrante; Chang et al.). The most frequently used method for decompression of the thoracic outlet caused by a CR is its resection (Henry et al.). The literature reports two resection methods for cervical ribs. The first is the transaxillary approach and the second is the supra-clavicular approach.

Many authors have come to the consensus on the greater difficulty of the trans-axillary approach, which is particularly preferred for the resection of the brachial plexus and decompression of the more inferior parts of the first rib. However, there is a much higher probability of injury to the brachial plexus and vessels (Chang et al.; Henry et al.). Although the supra-clavicular approach is an easier method, there are some drawbacks, including the lack of adequate vision for the complete exploration and repair of vessels in any large vessel injury (Chang et al.). However, it is a less invasive approach. This method has been reported to be more frequently saved for cases with more pronounced compression in the superior parts of the brachial plexus, with greater culpability of the compression of the anterior scalene muscle, or with or without vascular compression (Abdel Ghany et al.). In the present case, this method was preferred for the resection of the cervical rib due to the convenient palpation of lateral or distal parts of the aberrant rib, through the skin and supraclavicular area. The cervical rib was used as a landmark during surgical dissection. The body of the cervical rib was dissected tracing a route towards the vertebral body in the proximal part and the first rib in the distal part. This approach is also considered a safer approach for subclavian artery and brachial plexus as the surgical field is limited initially in the superior and later in the posterior region, in general, of these important structures (Spadlin´ski et al.; ^{Yi et al., 2017}).

The most important fact remains, as to what is the clinical effectiveness of different morphometric CR? The relationship between TOS and morphometry of the CR has not been emphasized in previous publications (Henry et al.). For this reason, there is no similarity of this article due to the morphometric contribution and, this case for a morphometric property of CR is a good visual example as the transformation of the seventh cervical vertebrae into a thoracic vertebrae (Li et al.).

CONCLUSION

In fact, since ribs are anatomic elements that are only connected to the thoracic vertebrae, there is no use of the prefix "thoracic" before of their names. In the light of the previous information in the literature, we concluded that it would be inaccurate to make an anatomical nomenclature only with the prefix "cervical" and that there is need for a separate nomenclature, for complete ribs connected to the cervical vertebra as in the present case. Therefore, we have named this type of real rib, attached to the C7, as the "zeroth rib", which would make a clearer distinction than other cervical ribs because this type CR is the final version in the transformation of C7 to a thoracic vertebrae.