The Spine Journal 15 (2015) 207
Congenital absence of the posterior right hemiarch The normal atlas is ring-like and consists of anterior and posterior arches and two lateral masses. However, at times, the posterior atlas arches can present congenital defects that range from midline clefts to total absence of the posterior arch [1]. Knowledge of congenital posterior atlas defects is useful to avoid misdiagnosis, especially in patients with cervical trauma where the anomaly can be mistaken for a fracture [2]. Type B congenital atlas arch defects are those presented as unilateral clefts, ranging from a small defect to the complete absence of one hemiarch [1]. In this context, a 68-year-old woman underwent an emergency radiologic study after a head and neck trauma that revealed an unusual, complete absence of the right posterior atlas hemiarch, classified as a Type B defect (Figure). Anatomical variations such as Type B congenital defects are reported to occur in less than 0.70% of the population [3,4]. Special care must be taken to avoid a misdiagnosis between an atlas fracture and an atlas defect during a radiologic examination after an acute trauma.
References [1] Currarino G, Rollins N, Diehl JT. Congenital defects of the posterior arch of the atlas: a report of seven cases including an affected mother and son. AJNR Am J Neuroradiol 1994;15:249–54. [2] Beaumont Caminos C, Zazpe Cenoz I, Hernandez Galan A, Jean Louis C, Fenandez Esain B, Gimena Ramos I. Partial agenesis of the posterior arch of the atlas. Am J Emerg Med 2008;26:118.e3–5. [3] Senoglu M, Safavi-Abbasi S, Theodore N, Bambakidis NC, Crawford NR, Sonntag VK. The frequency and clinical significance of congenital defects of the posterior and anterior arch of the atlas. J Neurosurg Spine 2007;7:399–402. [4] Sanchis-Gimeno JA, Blanco-Perez E, Aparicio L, Martinez-Soriano F, Martinez-Sanjuan V. Difficulties in distinguishing between an atlas fracture and a congenital posterior atlas arch defect in postmortem analysis. Forensic Sci Int 2014;242:e1–5.
Esther Blanco-Perez, MDa,b Luis Aparicio, MD PhDb Juan A. Sanchis-Gimeno, MD PhDb a Department of Radiology University Hospital de La Ribera Carretera de Corbera km 1, E-46600 Alzira, Valencia, Spain b Department of Anatomy and Human Embryology University of Valencia Faculty of Medicine University of Valencia Av. Blasco Ibanez, 15, E-46010 Valencia, Spain FDA device/drug status: Not applicable. Author disclosures: EB-P: Nothing to disclose. LA: Nothing to disclose. JAS-G: Nothing to disclose.
Figure. Axial computed tomography scan of the atlas showing congenital absence of the posterior right hemiarch (Type B defect). http://dx.doi.org/10.1016/j.spinee.2014.09.009 1529-9430/Ó 2015 Elsevier Inc. All rights reserved.
Congenital absence of the posterior right hemiarch The normal atlas is ring-like and consists of anterior and posterior arches and two lateral masses. However, at times, the posterior atlas arches can present congenital defects that range from midline clefts to total absence of the posterior arch [1]. Knowledge of congenital posterior atlas defects is useful to avoid misdiagnosis, especially in patients with cervical trauma where the anomaly can be mistaken for a fracture [2]. Type B congenital atlas arch defects are those presented as unilateral clefts, ranging from a small defect to the complete absence of one hemiarch [1]. In this context, a 68-year-old woman underwent an emergency radiologic study after a head and neck trauma that revealed an unusual, complete absence of the right posterior atlas hemiarch, classified as a Type B defect (Figure). Anatomical variations such as Type B congenital defects are reported to occur in less than 0.70% of the population [3,4]. Special care must be taken to avoid a misdiagnosis between an atlas fracture and an atlas defect during a radiologic examination after an acute trauma.
References [1] Currarino G, Rollins N, Diehl JT. Congenital defects of the posterior arch of the atlas: a report of seven cases including an affected mother and son. AJNR Am J Neuroradiol 1994;15:249–54. [2] Beaumont Caminos C, Zazpe Cenoz I, Hernandez Galan A, Jean Louis C, Fenandez Esain B, Gimena Ramos I. Partial agenesis of the posterior arch of the atlas. Am J Emerg Med 2008;26:118.e3–5. [3] Senoglu M, Safavi-Abbasi S, Theodore N, Bambakidis NC, Crawford NR, Sonntag VK. The frequency and clinical significance of congenital defects of the posterior and anterior arch of the atlas. J Neurosurg Spine 2007;7:399–402. [4] Sanchis-Gimeno JA, Blanco-Perez E, Aparicio L, Martinez-Soriano F, Martinez-Sanjuan V. Difficulties in distinguishing between an atlas fracture and a congenital posterior atlas arch defect in postmortem analysis. Forensic Sci Int 2014;242:e1–5.
Esther Blanco-Perez, MDa,b Luis Aparicio, MD PhDb Juan A. Sanchis-Gimeno, MD PhDb a Department of Radiology University Hospital de La Ribera Carretera de Corbera km 1, E-46600 Alzira, Valencia, Spain b Department of Anatomy and Human Embryology University of Valencia Faculty of Medicine University of Valencia Av. Blasco Ibanez, 15, E-46010 Valencia, Spain FDA device/drug status: Not applicable. Author disclosures: EB-P: Nothing to disclose. LA: Nothing to disclose. JAS-G: Nothing to disclose.
Figure. Axial computed tomography scan of the atlas showing congenital absence of the posterior right hemiarch (Type B defect). http://dx.doi.org/10.1016/j.spinee.2014.09.009 1529-9430/Ó 2015 Elsevier Inc. All rights reserved.
