Variation in the Occurrence of Median Occipital Condyle and Its Impact on Atlanto-Occipital Joint and Atlantoaxial Stability R

Research Article

Variation in the occurrence of median occipital condyle and its impact on atlanto-occipital joint and atlantoaxial stability R. Ashwin Kumar1, K. Yuvaraj Babu2, Karthik Ganesh Mohanraj2*

ABSTRACT

Introduction: The third occipital condyle is a constituent part of median occipito-atlanto-odontoid joint. The third condyle also known as median occipital condyle is a rare anatomic variant of the occipital condyles. It is a small separate ossicle at the anteromedial margin of the occipital condyle formed by the failure of the embryonic proatlas to unite with the condyle proper. In higher mammals like humans, it may contribute to anomalous structures around the foramen magnum which is referred as the third occipital condyle. Materials and Methods: In the present study, a total of 50 dry human skulls of unknown sex and without any gross breakage were used. All the skulls were subjected for visual and morphological analysis of third occipital condyle at the midpoint of the anterior part of foramen magnum. The presence of the third occipital condyle and its prevalence were noted and analyzed. Results: The third occipital condyle is observed only in four skull bones (8%). It was photographed and analyzed for its prominence. Conclusion: The anatomical variations of the presence of the third condyle can be explained by the different degrees of persistence. A small third occipital condyle located in the median-sagittal plane at the midpoint of the anterior margin of foramen magnum represents the highest degree of persistence. If the third occipital condyle is present, it may serve as an articulating facet for the tip of the dens or with the anterior arch of the atlas.

KEY WORDS: Atlanto-occipital joint, Foramen magnum, Occipital condyle, Proatlas, Third occipital condyle

INTRODUCTION tubercle” is a rare osseous anatomical variation of the occipital condyles in the skull.[1] In humans, it is found in There are several anatomical, developmental, and approximately 0.5% of the total population. It is a small evolutionary variations at the craniovertebral region, and separate bony ossicle or tubercle rarely present at the especially in the craniocervical area, which can reflect midpoint of anteromedial margin of foramen magnum developmental deformities due to birth anomalies. Such between the occipital condyles. It is formed due to the anatomical osseous variations may be a minor one but failure of fusion between the embryonic proatlas and can cause severe problems in diagnosing. An accurate the condyle proper.[2] The third occipital condyle is a and clear radiological diagnosis involves a thorough constituent part of a median occipito-atlanto-axial .[3] and extensive knowledge on the morphological features joint In the lower vertebrates, the cranial half of the of both normal and abnormal variations with the first cervical sclerotome forms a separate bone between manifestation of their characteristic features in a common the atlas and occipital bone called as the proatlas. In man, it may contribute to anomalous structures around radiology. Among several osseous rare variations, the the anterior margin of the foramen magnum.[4] occurrence of the third occipital condyle is noteworthy. The presence of this atypical variation forms a The third occipital condyle also known as “condylus rare component of the occipito-atlanto-axial joint. tertius” or “median occipital condyle” or “basilar Atlantoaxial instability occurs as a result of either a bony or ligament abnormality which is characterized Access this article online by the presence of excessive movement at the junction [3] Website: jprsolutions.info ISSN: 0975-7619 between the axis and atlas. In humans, the occipital bone is formed by the union of the sclerotomes

1Department of Anatomy, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India, 2Department of Anatomy, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India

*Corresponding author: Karthik Ganesh Mohanraj, Department of Anatomy, Saveetha Dental College, Saveetha Institute of Medical and Technical Science, Saveetha University, 162, Poonamallee High Road, Chennai - 600 077, Tamil Nadu, India. Phone: +91-9940545168. E-mail: [email protected]

Received on: 07-04-2018; Revised on: 16-05-2018; Accepted on: 21-06-2018

1896 Drug Invention Today | Vol 10 • Issue 10 • 2018 R. Ashwin Kumar, et al.

b c Figure 1: (a) Norma basalis. (b) Enlarged view of the base of the normal skull. (c) Enlarged view of the base of the skull with condylus tertius; the arrow points to the bony process in the median line at the anterior margin of the foramen magnum between the occipital condyles corresponding to the roots of the hypoglossal nerve occipital condyle was just a small tubercular structure during development.[4] without any facet. The presence of such type of tubercle falls under true third occipital condyle. It was Anatomical variations and abnormalities of the photographed and presented for its prominence Figure 1. craniovertebral junction are of primary choice of study not only to anatomists but also to clinicians, DISCUSSION anthropologists, etc. Due to the presence of such variations and malformations, several neurological The third occipital condyle was first described by J.F. symptoms and death may be possible.[5] Some findings Meckel in the year 1815 and reported as a bony process are reported as a simple round tubercle, whereas in in the midpoint of the anterior midline of the foramen the others, it was found to be an articular facet which magnum between the occipital condyles.[6] In humans, receives the tip of the odontoid process forming a joint its presence is rare. However, it is always present in variety of true diarthrosis.[5] The skull bone presents reptiles. If present functionally, it may serve as an different anatomical variations and most of these upper articular facet with the tip of the dens or with occurrences are the consequence of developmental the anterior arch of atlas. The third occipital condyle anomalies or may be due to the influence of the is a vestige of proatlas.[7] The anatomical appearances external environment. Nevertheless, the abnormal of the variations of the third occipital condyle may be anatomical existence pampers much on the regular justified by the different degrees of persistence and lifestyle activities or even on the conditions during occurrence.[8] surgical emergencies. These types of studies throw light on various anatomical variations during medical In a study performed on 600 skulls, some suggestions of craniovertebral malformations, including a third treatment and surgeries. Thus, the aim of the study is to [9] study and analyze the presence of the rare variation of condyle, were present in 14%. The study conducted the third occipital condyle in dry human skull bones. by Von Hayek found third occipital condylar bone formation commonly in lower animals.[10] Schumacher integrated it among the expressions of the arcus MATERIALS AND METHODS prebasi-occipitalis. It is generally present in the midline The present study was conducted on a total of 50 of the anterior margin of foramen magnum but may dry human skull bones of unknown sex and without be paramedian or paramedially present on both sides any gross breakage which was collected from the of the midpoint which is referred to as the false third Department of Anatomy, Saveetha Dental College. occipital condyle. Such abnormal bone can result in The skulls were subjected for visual and morphological neural compression and vascular compromise and can analysis, and evaluation of the presence of the third be apparent with abnormalities in cerebrospinal fluid [11] occipital condyle and its prevalence was studied. dynamics causing detrimental effects. Menezes and Fenoy recognized a reduction of the volume of RESULTS the posterior cranial fossa as a result of the anomaly and reported the presence of Chiari malformation in The third occipital condyle is observed with slight that subject.[12] The anterior tubercle of the clivus is prominence only in one skull bone. The observed third formed by the hypocentrum of the fourth occipital

Drug Invention Today | Vol 10 • Issue10 • 2018 1897 R. Ashwin Kumar, et al. sclerotome (proatlas). The apex of the dens is formed occipito-atlanto-odontoid joint: A case report. Surg Radiol Anat by centrum. The formations of the occipital condyles 2002;24:71-6. 4. Jayanthi V, Kulkarni R, Kulkarni RN. Atlanto-occipital fusion- are contributed by the rostral ventral neural arch, report of two cases. J Anat Soc India 2003;52:71-3. third condyle, and the anterior rim of the foramen 5. Figueiredo N, Moraes LB, Serra A, Castelo S, Gonsales D, magnum.[13] The dorsal caudal part of the neural arch Medeiros RR, et al. Median (third) occipital condyle causing forms the posterior arch of atlas and the lateral atlantal atlantoaxial instability and myelopathy. Arq Neuropsiquiatr [14] 2008;66:90-2. masses. The occurrence of anterior tubercle from 6. Meckel JF. About some abnormalities of the bones. Dtsch Arch the anterior end of foramen magnum corresponds to Physiol (Halle/Berlin) 1815;1:641-4. the abnormality of the proatlas at hypocentrum.[15,16] 7. Putz R. On the manifestation of hypochordal braces in the craniovertebral border area in humans. Anat Anz 1975;137:65- The third occipital condyle is an embryological 74. 8. Friedlowsky A. On the so-called accessory joint stools on the remnant of the proatlas sclerotome and is a rare pars basilaris ossis occipitis and some forms of unusual joint anomaly of the craniovertebral junction which can connection between the epistropheus tooth process and the lead to instability of joints and compression of occipital bone. Seat Ber Akad Wiss Vienna 1869;60: 319-42. important surrounding neurovascular structures.[17] A 9. Lang J. Clinical Anatomy of the Head. Berlin: Springer-Verlag; 1983. 10. Von Hayek H. Uber on the fate of the Proatlas and on the few rare cases of abnormal variation of the presence of development of the head joints in reptiles and birds. Morph Jb [18,19] third occipital condyle have been reported. Such 1924;53:137. abnormal variation reported an increased atlantodental 11. Von Schumacher S. A contribution of the manifestation of the interspace with a retroflexed odontoid process as occipital vertebra. Anat Anz 1907;31:145. [1] 12. Menezes AH, Fenoy KA. Remnants of occipital vertebrae: Proatlas revealed by plain radiographs. Accurate knowledge segmentation abnormalities. Neurosurgery 2009;64:945-53. about the development and imaging modalities of 13. Goel A, Shah A. Unusual bone formation in the anterior rim such rare anomalies is extremely useful in the prompt of foramen magnum: Cause, effect and treatment. Eur Spine J diagnosis and management of such patients during 2010;19 Suppl 2:S162-4. 14. Kotil K, Kalayci M. Ventral cervicomedullary junction related surgical procedures. compression secondary to condylus occipitalis (median occipital condyle), a rare entity. J Spinal Disord Tech 2005;18:382-4. CONCLUSION 15. Shaffrey CI, Chenelle AG, Abel MF, Menezes AH, Wiggins GC. Anatomy and physiology of congenital spinal lesions. In Benzel The third occipital condyle or the median occipital EC, editor. Spine Surgery: Techniques, Complication Avoidance, and Management. 2nd ed. Amsterdam: Elsevier; 2005. p. 61-87. condyle is sometimes associated with atlantoaxial 16. Fadzil F. Median occipital condyle associated with atlantoaxial instability. The presence of such rare abnormality instability and myelopathy: A case report. Med J Malaysia of the craniovertebral junction may lead to several 2011;66:365-6. clinical complications. Myelopathy is one such 17. Baumgarten M, Mouradian W, Boger D, Watkins R. Computed axial tomography in C1-C2 trauma. Spine (Phila Pa 1976) important problem of this abnormality. A complete 1985;10:187-92. thorough findings and studies may be needed for 18. Kowalski HM, Cohen WA, Cooper P, Wisoff JH. Pitfalls in better understanding of its role in the management of the CT diagnosis of atlantoaxial rotary subluxation. AJR Am J such anomalous variation. Roentgenol 1987;149:595-600. 19. Mönckeberg JE, Tomé CV, Matías A, Alonso A, Vásquez J, Zubieta JL, et al. CT scan study of atlantoaxial rotatory REFERENCES mobility in asymptomatic adult subjects: A basis for better understanding C1-C2 rotatory fixation and subluxation. Spine 1. Prescher A, Brors D, Adam G. Anatomic and radiologic (Phila Pa 1976) 2009;34:1292-5. appearance of several variants of the craniocervical junction. Skull Base Surg 1996;6:83-94. 2. Rao PV. Median (third) occipital condyle. Clin Anat 2002;15:148-51. 3. v Lüdinghausen M, Schindler G, Kageyama I, Pomaroli A. Source of support: Nil; Conflict of interest: None Declared The third occipital condyle, a constituent part of a median

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