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INTRODUCTION
According to standard anatomical textbooks, the external jugular vein (EJV) is chiefly responsible for draining the scalp and face and is formed by the union of the posterior division of the retromandibular vein and posterior auricular vein near mandibular angle (Standring et al., 2012; Sinnatamby, 2011). It then descends diagonally, superficial to the sternocleidomastoid muscle to reach the subclavian vein (Standring et al.). The internal jugular vein (IJV) begins from the posterior compartment of the jugular foramen and is a continuation of the sigmoid sinus (Standring et al.; Sinnatamby). It is located within the carotid sheath with the common carotid artery and the vagus nerve and unites with the subclavian vein to form the brachiocephalic vein (Standring et al.; Sinnatamby). In addition, variations in the formation, lengths and drainage patterns of EJV and IJV has been documented in adults (Choudhry et al., 1997; Nayak, 2006; Downie et al., 2007), however reports of fetal studies are minimal. Alaani et al. (2005) stated that unilateral duplication of the IJV is rare. Downie et al. classified the variations of IJV into two patterns: duplicate and fenestrated. They further described that duplication which was limited to those cases where the branches of IJV remain separate over the entire course, while fenestration should be used for the case in which the branched vessel reunites into a single “normal” vessel. In 1937, Pikkieft reported duplication of EJV in 5.3 % of their dissections, while Olabu et al. found that 2.2 % of their sample had a duplicate EJV.
Furthermore, the IJV is of clinical importance to clinicians as inspection, auscultation and Dopplerultrasonic examinations of these veins provide evidence that may aid in the diagnosis of cardiac diseases (Balachandra et al., 2012). Consequently, dilatation of the jugular veins may be a result of compression of the superior vena cava, which indicates potential pathologies within the mediastinum or pericardial sac (Balachandra et al.). Therefore, knowledge regarding variation pattern of the external and internal jugular veins are important to clinicians performing vascular surgeries in head and neck region, as well as those performing angioplasty, catheterization and occasionally hemodialysis (Sankar & Bhanu, 2011; Balachandra et al.). Therefore this study aims to highlight variation patterns of external and internal jugular veins, which were observed during the gross anatomical micro-dissection of the anterior and posterior triangles of the neck in 40 fetuses (n=80).
MATERIAL AND METHODS
General: This study conducted a bilaterally dissection of 40 fetuses between the gestational ages of 15-28 weeks. The fetal specimens were obtained from Clinical Anatomy, School of Laboratory Medicine and Medical Science at the University of KwaZulu-Natal (Westville and Nelson Mandela School of Medicine campuses). Ethical clearance was obtained (BF: 156/07) and complied with the regulations of the National Health Act 61 of 2003.
Methodology: The sternocleidomastoid muscle was removed from its attachment to the clavicle and mastoid process. The lesser occipital, great auricular, transverse cervical and supraclavicular nerves were preserved. The fascia covering the floor of the posterior triangle was removed by fine dissection and the scalene muscles, levator scapulae muscle and splenius capitus muscle were exposed and identified. The common carotid artery, vagus nerve and internal jugular vein were dissected to expose its relationship to the ansa cervicalis. The dissections were recorded using a Canon digital Powershot G5 camera (4x optical zoom).
RESULTS
Variations of the External Jugular Vein. Duplication of EJV. In 3/80 (4 %) of the fetal specimens, a duplicated EJV (with an “H” shaped communication joining the two), was located on the sternocleidomastoid muscle (SCM). The transverse cervical vein (TCV) drained into one part of the EJV. The transverse cervical nerve (TCN) intertwined with EJV (Fig. 1).
Variations of the Internal Jugular Vein. “Y”- shaped IJV. In 1/80 (1 %) of the fetal specimens, the internal jugular vein had a “Y” shaped appearance. The upper part of the superior root of the ansa cervicalis was located at the junction of the “Y” (indicated by arrow) and a lower part was located medial to the internal jugular vein (Fig. 2).
“Y”-shaped IJV with a tributary from EJV. In 2/80 (3 %) of the fetal specimens, the internal jugular vein divided into two and received a tributary from the external jugular vein superiorly and inferiorly. Furthermore, the ansa cervicalis looped around the lower end of the internal jugular vein (Fig. 3).
DISCUSSION
The knowledge of anatomical variations of the jugular veins is significant for any venous ligations conducted during surgical procedures, such as radical neck dissections (Balachandra et al.).
The EJV has been reported to show a number of variations that may affect its tributaries, size, drainage, form, course and termination (Pikkieft; Salmeri et al., 1991; Choudhry et al.; Yadav et al., 2000; Singla et al., 2011). The duplication of the EJV occurred in 4 % of the specimens in this study, furthermore the transverse cervical vein drained into one part of the EJV, while the transverse cervical nerve intertwined with the EJV. In an earlier study conducted by Pikkieft, it was found that the EJV was duplicated in 5.3 % of their sample. Furthermore, Olabu et al. reported that in 2.2 % of their Kenyan sample, the EJV was duplicated. However, Choudhry et al. reported that the EJV split into two parts on the external surface of the SCM muscle but re-joined at the junction of the facial vein.
The internal jugular vein is the largest vein of the head and neck and it is a continuation of the sigmoid sinus which drains the intracranial and deep structures of the head and neck region (Standring et al.; Deepak et al., 2015). However, in this study, the internal jugular vein divided into two and received a tributary from the external jugular vein in 3 % of the sample. Similarly, Lalwani et al. recorded a rare venous communication between the EJV of one side, which drained into the IJV on the opposite side. In addition, Olabu et al. recorded that EJV terminated into IJV in 7.7 % of the cases studied.
In 1 % of the fetal specimens in this study, the internal jugular vein had a “Y” shaped appearance. Biondi et al. (2009) recorded that the right jugular vein bifurcated about 2 cm from the jugular foramen and drained into the right subclavian vein (Deepak et al.).
Rossi & Tortori-Donati (2001) postulated that the duplication of vessels may occur in the third and the sixth week of the gestational development as a result of developmental derangement (Snoj & Cvetko, 2013). Furthermore, it has been stated that IJV duplication is frequently recorded to be associated with phlebectasia, which suggests abnormalities in the development of the venous wall, perhaps involving incomplete development of the muscular layer (Som et al., 1985; Rossi & Tortori-Donati; Turan-Ozdemir et al., 2004; Snoj & Cvetko). Dodo (1986) suggested that the jugular foramen has a bony partition that may be caused by an intra-jugular process of occipital bone, this partition may result in duplication of IJV (Sankar & Bhanu).
CONCLUSION
This study observed three variations in the pattern of the EJV and IJV. With regard to the EJV, duplication occurred in 4 % of the specimens. The “Y-shaped” IJV occurred in 1 % of the specimens; however the “Y-shaped” IJV gave off a tributary to the EJV in 3 % of the specimens sampled. Knowledge of these variable patterns of the external and internal jugular veins is of clinical import.
