UNCOMMON OSSEOUS BRIDGE OF THE ATLAS IDENTIFIED ON CERVICAL SPINE RADIOGRAPHY: PONTICULUS POSTICUS CASE SERIES

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1 Revista Română de Anatomie funcţională şi clinică, macro- şi microscopică şi de Antropologie Vol. XV Nr CLINICAL ANATOMY UNCOMMON OSSEOUS BRIDGE OF THE ATLAS IDENTIFIED ON CERVICAL SPINE RADIOGRAPHY: PONTICULUS POSTICUS CASE SERIES A.H. Nedelcu¹, R.T. Tepordei¹, Iolanda Augustin 2, Simona Partene Vicoleanu¹, Mihaela Mitrea¹, T. Taranu¹, M. Gutu 3*, C.I. Stan 1, Manuela Ursaru 4 Gr.T. Popa University of Medicine and Pharmacy, Iaşi 1. Department of Morphofunctional Science I 2. Student 3. Department of Morphofunctional Science II 4. Department of Surgery II UNCOMMON OSSEOUS BRIDGE OF THE ATLAS IDENTIFIED ON CERVICAL SPINE RADIOGRAPHY: PONTICULUS POSTICUS CASE SERIES (Abstract): Ponticulus posticus is a fortuitous finding on cervical radiographs and consists of an anomalous bone bridge between superior articular process and superior margin of the atlas s posterior arch. This malformation has many terms in medical literature: arcuate foramen, foramen sagittale or Kimmerle anomaly. The diagnosis methods include cervical radiography, computed tomography and cone-beam computed tomography. Different patterns of headache where stated in medical literature, varying between simple headache, cervical pain syndrome or even migraine. Our aim is to underline the importance of the cervical radiography in diagnosis of arcuate foramen and to point out the clinical symptoms it may generate. Key words: PONTICULUS POSTICUS, ARCUATE FORAMEN, VERTEBRAL ARTERY, CERVICAL RADIOGRAPHY INTRODUCTION Atlas, the first cervical vertebra (C1), is a particular vertebra due to its morphological aspect. It consists of two lateral masses connected by anterior and posterior arches. It is the only vertebra without a body. The posterior arch is longer, about twice the size of the anterior one and has two oblique grooves situated on its superior surface, near the lateral masses, corresponding to the horizontal course of the vertebral arteries between foramen transversum and foramen magnum (1). The grooves are bounded superiorly by atlanto-occipital membrane that connects the C1 with the occipital bone. Ponticulus posticus is a relatively frequent anomaly of the atlas generated by the ossification process of the lateral side of the oblique atlanto-occipital membrane. As a result, a bone bridge appears between the posterior surface of the superior articular process and superior margin of the posterior arch of the atlas forming a foramen through which the vertebral artery (V3 segment) and suboccipital nerve pass (1, 2). This anatomical variant has many terms in medical literature: arcuate foramen, canalis arteriae vertebrale, foramen sagittale, foramen atlantoideum posterior or Kimmerle anomaly. The most commonly used is ponticulus posticus, the Latin term for little posterior bridge (3). The origin of this malformation is disputed between different authors. Some adopted the congenital theory sustained by the fact that its frequency varies between the ethnic groups, race or family members (4), while others conclude that arcuate foramen develops during lifetime, in direct relation with environment and labour habits (5, 6, 7). This theory is endorsed by studies which show a lower frequency of ponticulus posticus in children than in adults (5). Schilling J. et al. (7) suggest that arcuate foramen is a functional readjustment so that vertebral artery and suboccipital nerve are protected from compression. 387

2 A.H. Nedelcu et al. Fig. 1. Anatomical sample: white star arcuate foramen, white arrow bone bridge. the cervical radiography in diagnosis of arcuate foramen and to point out the clinical symptoms it may generate. Fig. 2. Plain radiograph lateral projection: yellow arrow incomplete ponticulus posticus Few morphological subtypes are mentioned, depending on the completion and localization of the ossification process - bilateral or unilateral. Thus, in clinical practice, the arcuate foramen may vary between unilateral incomplete, unilateral complete, bilateral incomplete to bilateral complete foramen. A particular situation associates a complete with a contralateral incomplete foramen. The arcuate foramen is identified by the instrumentality of few imagistic methods like radiograph, cone beam computer tomography (CBCT) or spiral computer tomography (CT). It is also observed during the cadaveric dissection of the cervical region or in dry atlas samples. Our aim is to underlie the importance of CASE REPORTS We exhibit a dry specimen of C1 followed by five trauma patients without injuries of the cervical spine in which we identified different morphological variants of ponticulus posticus. They were investigated at Emergency Department of Sf. Spiridon Hospital Iassy using the Moviplan 800BF radiological system and, for the fifth patient, images were recorded on Siemens Somatom Emotion 16 CT Scanner in the Radiology Department. All the images were processed with the Radiant DICOM Viewer software. Anatomical sample: We studied the bone collection of the University of Medicine and Pharmacy Gr. T. Popa Iassy Anatomical Institute. One of the C1 samples offers us a good support to study the arcuate foramen. The atlas vertebra we found has bilateral bonny bridges between the superior aspect of the posterior arch and retroglenoid tubercles of the superior articular processes and extend above the grooves of vertebral arteries completing the two arcuate foramens. It corresponds to a complete bilateral morphologic type (fig. 1). Case 1 19-year-old female with cranial trauma, consequence of aggression, reaches the Emergency Department of Sf. Spiridon Hospital Iassy. The plain radiographs show no cranial and spinal injuries. Instead, on lateral projection, we identified a short linear opacity about 5.3 mm long and 3.2 mm in width at the base. It starts cranially at the superior articular pro- 388

3 Uncommon Osseous Bridge of the Atlas Identified on Cervical Spine Radiography Fig. 3. Plain radiograph lateral projection: yellow arrow complete ponticulus posticus Fig. 4. Plain radiograph lateral projection: yellow arrow ponticulus posticus, red arrow cervical block cess of the atlas and descends over the superior aspect of the posterior arch without reaching it. The morphology of the bone bridge suggests an incomplete unilateral ponticulus posticus (fig. 2). Case 2 41-year-old female with trauma, consequence of a car accident, was brought by Ambulance Service. On cervical radiograph, lateral projection, we identified a thin linear opacity over the posterior arch of the atlas. It is about 13.5 mm long and 1.7 mm thick. It enlarges towards the extremities, reaching a width of 3.1 mm cranially and 3.6 mm caudally. Its thickness and the morphology of the foramen it forms suggest a complete unilateral type (fig. 3). Case 3 29-year-old male is brought to the Emergency Department of Sf. Spiridon Hospital after a car accident. No traumatic injury of the head and cervical spine were found. The lateral projection X-ray shows a large bone bridge between the posterior arch of the atlas and superior articular process, 16.7 mm long, 5.1 mm in width at the cranial extremity, 4.1 mm width of the intermediary segment and 8.7 mm in width at the caudal extremity. It is also associated with a linear opacity on the superior aspect of the posterior arch, 7.2 mm long and 5.1 mm in width caudally, that suggests an incomplete bone lamina. The radiological aspect hints at the association of the complete type with contralateral incomplete type. This radiograph also revealed a C3-C4 cervical block (fig. 4). Case 4 66-year-old male addressed to Emergency Department following physical aggression. The first line of imagistic investigations includes plain radiographs of cervico-cranial region as well as the abdominal ultrasonography. On cervical X-ray profile view, we detect two parallel bone laminae which connect the posterior arch with the superior articular processes of the atlas. The lengths of the two bridges are 9.3 mm and 9.2 mm. The widths are about 1 mm cranially, 0.7 mm intermediary and 2 mm caudally, 389

4 A.H. Nedelcu et al. Fig. 5. Plain radiograph lateral projection: yellow arrow bilateral ponticulus posticus respectively 0.9 mm cranially, 1.1 mm intermediary and 2 mm caudally. The appearance of both opacities representing the bridges is due to a slight rotation of the patient s head during examination. No other injuries or trauma were found. The image suggests a complete bilateral morphologic aspect (fig. 5). Case 5 54-year-old male addressed to Emergency Department of Sf. Spiridon Hospital Iassy for a fall due to syncope. The history revealed headache and vertigo as well as frequent neck pain associated with migraine. He was guided to Radiology Department where cranio-cerebral and cervical CT scans were performed. The bone window reveals the presence of a complete ponticulus posticus passing over the left vertebral artery and an incomplete type on the right side (fig. 6). DISCUTIONS The ponticulus posticus is a morphologic variant of the atlas with a disputed frequency between authors. To our data, its prevalence stretches between %, varying within population, age or study type: cadaveric, dry samples, X-ray or CT scan (1, 7, 8, 9, 10). A higher incidence related to ethnic groups is registered in India, Gulbarga Region, where the arcuate foramen is found in 60% of the patients included in the study (5), compared with Turkish (36.8%), Russians (15-18%), Italians (16.7%), or Koreans (15.5%) (1, 8, 10, 11). In their meta-analysis, Elliott RE et Tanweer O. (13) stated that the prevalence of Kimmerle anomaly is 16.7%, with a higher incidence on dry bone/cadaveric studies versus imagistic studies. The overall sex prevalence does not appear to have statistical significance (5, 12, 13), only Sekerci AE et al. finding a higher frequency in males than in females (1). Miki T et al. (14) proposed in 1979 a radiological classification of the ponticulus posticus. Accordingly, we can describe three morphological types: i) Complete ii) Incomplete and iii) Calcification. The most frequent is the incomplete type (1, 9, 11, 12), meanwhile the unilateral phenotype is more common than bilateral phenotype (8, 12, 13). The clinical manifestations include orofacial pain, vertigo, diplopia, neck pain, headache and migraine. Chitroda P.K. et al. (5) conclude that clinical manifestations are correlated with morphological phenotypes. In his study, 76% of the patients diagnosed with complete form of ponticulus posticus were symptomatic while only 14% of incomplete form caused symptoms. No gender difference was noted, the symptoms frequency being equal for females and males. In order to correlate the imagistic morphologic aspects to clinical manifestations, we suggest a new anatomo-clinic classification of ponticulus posticus: Type I: unilateral incomplete Type II: bilateral incomplete Type III: unilateral complete Type IV: mixt associating complete bridge with contralateral incomplete bridge Type V: bilateral complete This improved classification helps the clinicians to adjust their prognostic according to morphological phenotypes, bearing in mind that different degree of calcification will affect the blood flow into the vertebral artery. In a mandatory study, Chaplygina YV et al. (8) demonstrate a statistically significant asymmetry of flux velocity for 78.5% of the patients diagnosed with ponticulus posticus. 390

5 Uncommon Osseous Bridge of the Atlas Identified on Cervical Spine Radiography Fig. 6. Multiplanar computed tomography reconstruction: (A) yellow arrow complete ponticulus posticus; (B) red arrow incomplete ponticulus posticus The CT scan is more sensitive than plain radiograph technique but the statistical signification was not always demonstrated (8, 13). Nevertheless, Cho YJ (11) and Kim KH et al. (12), in their comparative studies, found a significant difference between X-ray and spiral CT related to diagnosis of arcuate foramen. According to the authors, the spiral computed tomographic exploration associated with multiplanar reconstruction should be performed for preoperative planning of C1 lateral mass screw insertion (13). CONCLUSION Ponticulus posticus is a relatively frequent anomaly of the atlas which is often revealed on lateral projection plain radiograph. It can be responsible for various symptoms with cervical and cephalic localisation. To certify the diagnosis, plain lateral radiographs of the cervical region are usually sufficient but, for accurately identify the morphological type as well as taking precise measurements, the spiral computed tomographic exploration is mandatory, especially in the selected surgical cases. BIBLIOGRAFIE 1. Sekerci AE, Soylu E, Arikan MP, Ozcan G, Amuk M, Kocoglu F. Prevalence and Morphologic Characteristics of Ponticulus Posticus: Analysis Using Cone-Beam Computed Tomography. J Chiropr Med Sep; 14(3): Bayrakdar IS, Miloglu O, Altun O, Gumussoy I, Durna D, Yilmaz AB. Cone beam computed tomography imaging of ponticulus posticus: prevalence, characteristics, and a review of the literature. Oral Surg Oral Med Oral Pathol Oral Radiol Dec; 118(6):e Young JP, Young PH, Ackermann MJ, Anderson PA, Riew KD. The ponticulus posticus: implications for screw insertion into the first cervical lateral mass. J Bone Joint Surg Am. 2005; 87: Crowe H.S. The ponticulus posticus of the atlas vertebra and its significance. Upper Cerv Monogr.1986; 4(1): Chitroda PK, Katti G, Baba IA, Najmudin M, Ghali SR, Kalmath B. Ponticulus posticus on the posterior arch of atlas, prevalence analysis in symptomatic and asymptomatic patients of gulbarga population. J Clin Diagn Res Dec;7(12): Paraskevas G, Papaziogas B, Tsonidis C, Kapetanos G. Gross Morphology of The Bridges Over The Vertebral Artery Groove On The Atlas. Surg Radiol Anat. 2005; 27(2):

6 A.H. Nedelcu et al. 7. Schilling J, Schilling A, Suazo G I. Ponticulus posticus on the posterior arch of atlas, prevalence analysis in asymptomatic patients. Int. J. Morphol., 2010, 28(1): ,. 8. Chaplygina YV, Kaplunova OA, Dombrovskiy VI, Sukhanova P, Blinov IM, Fishman AY, Mukanyan SS. Morpho-functional characteristics of kimmerle anomaly. Morfologiia. 2015; 147(3): Simsek S, Yigitkanli K, Comert A, Acar HI, Seckin H, Er U,Belen D,Tekdemir I, Elhan A.Posterior osseous bridging of C1. J Clin Neuroscience, 2008; 15(6): Gibelli D, Cappella A, Cerutti E, Spagnoli L, Dolci C, Sforza C. Prevalence of ponticulus posticus in a Northern Italian orthodontic population: a lateral cephalometric study. Surg Radiol Anat Apr;38(3): Cho Y J. Radiological Analysis of Ponticulus Posticus in Koreans. Yonsei Med J Feb; 50(1): Kim KH, Park KW, Manh TH, Yeom JS, Chang BS, Lee CK. Prevalence and Morphologic Features of Ponticulus Posticus in Koreans: Analysis of 312 Radiographs and 225 Three-dimensional CT Scans, Asian Spine J Jun; 1(1): Elliott RE, Tanweer O. The prevalence of the ponticulus posticus (arcuate foramen) and its importance in the Goel-Harms procedure: meta-analysis and review of the literature. World Neurosurg Jul- Aug;82(1-2):e Miki T, Oka M, Urushidani H, Hirofuji E, Tanaka S, Iwamoto S. Ponticulus Posticus: Its Clinical Significance. Acta Medica Kinki Univ. 1979, 4(2): Corresponding author Mihai Gutu misugutu@yahoo.fr 392