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J Korean Soc Spine Surg. 2012 Mar;19(1):16-19. English.
Published online March 31, 2012.  https://doi.org/10.4184/jkss.2012.19.1.16
© Copyright 2012 Korean Society of Spine Surgery
The Inferior Accessory Ossicle of the Anterior Arch of the Atlas Misdiagnosed as Anterior Arch Fracture - A Case Report -
Yung Park, M.D., Hyoung Bok Kim, M.D., Sang Woo Jeon, M.D., Yun Tae Lee, M.D., Ju Hyung Yoo, M.D., Hyun Chul Oh, M.D., Joong-Won Ha, M.D., Seung Yong Sung, M.D., and Han Kook Yoon, M.D.
Department of Orthopedic Surgery, National Health Insurance Corporation Ilsan Hospital, Gyeonggi, Korea.
Department of Orthopedic Surgery, Yonsei University College of Medicine, Seoul, Korea.

Corresponding author: Joong-Won Ha, M.D. Department of Orthopedic Surgery, National Health Insurance Corporation Ilsan Hospital, Gyeonggi, South Korea. TEL: 82-31-900-0227, FAX: 82-31-900-0343, Email: esshappy@daum.net
Received March 11, 2011; Revised August 05, 2011; Accepted August 12, 2011.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Abstract

Study Design

Case report.

Objectives

We report a very rare case of the inferior accessory ossicle of the anterior arch of the atlas misdiagnosed as anterior arch fracture.

Summary of Literature Review

It is necessary to know the existence of inferior accessory ossicle of the anterior arch of the atlas, even though it is extremely rare.

Materials and Methods

A 29-year-old woman was referred to our emergency service unit with symptoms of neck pain and scalp laceration, after being involved in a car accident. She was diagnosed as the inferior accessory ossicle of the anterior arch of the atlas, by multiple diagnostic mordalities.

Results

The symptom of neck pain was relieved spontaneously, and her symptom has been relieved at her latest visit, as a follow up within 3 months.

Conclusions

It is important to be aware of cervical anatomical variants because we commonly confuse it with other pathologic conditions, such as a fracture and thus, misdiagnose the condition.

Keywords: Atlas; Inferior accessory ossicle; Anterior arch fracture


The rate of developing inferior accessory ossicle of the anterior arch of the atlas is extremely rare. As looking for literatures, there are some reported cases.1) In 1956 Kohler and Zimmer's described "Borderlands of the normal and early pathologic in skeletal roentgenology".2) Keats3) named the inferior accessory ossicle of the anterior arch of the atlas for the first time. It is a relatively large ossicle, roughly triangular shape with its base superiorly and located in the midline, right below the anterior arch of the atlas. This anomaly was considered as a benign variation and almost all of them are found as an incidental radiologic finding or patients can be presented with pain like symptom. However, when evaluating an acute neck trauma, it is important to be aware of this cervical anatomical variant because without it we easily make a misdiagnosis on the entity of fracture. This report discusses an extremely rare case of an anatomical variant of atlas which was misdiagnosed as an anterior arch fracture after a traffic accident.

CASE REPORT

A 29-year-old woman was referred to our emergency service unit with neck pain and scalp laceration after being involved in a car accident. The result of physical examination revealed tenderness of paraspinal tissues and the spinous processes; neurological examination had no abnormality. Her initial cervical radiograph study of lateral view suggested an anterior arch fracture(Fig. 1). Computed tomography(CT) images demonstrated ossicle located on the middle and a well corticated bone fragment below the anterior arch of atlas with no soft tissue swelling which means a fracture(Fig. 2). Magnetic resonance image(MRI) also showed no definite evidence of hematoma or soft tissue swelling(Fig. 3). We couldn't find out any evidence of traumatic injury on whole body bone scintigraphy(WBBS)(Fig. 4). The symptom of neck pain was relieved spontaneously, and her symptom has been relieved when she had a latest visit as a follow up within 3 months.


Fig. 1
Lateral radiograph of cervical spine shows a well corticated bone fragment inferior to the anterior arch of atlas (black arrow)
Click for larger image


Fig. 2
Lateral CT at the level of C1 showing inferior accessory ossicle of the anterior arch of atlas (white arrow).
Click for larger image


Fig. 3
T1 GD enhance MR image showing no definite evidence of hematoma and soft tissue swelling at the level of C1
Click for larger image


Fig. 4
Whole body bone scan showing normal finding.
Click for larger image

DISCUSSION

Accessory bones, or ossicles, are considered as normal anatomic variants.4) The information where the ossicle is and how it looks like is important for the radiologists for not being confused normal variants with demonstrations of pathological condition.3) These ossicles are particularly placed in the foot. However, the variant of inferior accessory ossicle of the anterior arch of the atlas is extremely rare.1)

The atlas has three ossification centers: And those are anterior ossification center that is composed of anterior tubercle, and two lateral centers from which the lateral masses and the posterior specimens from the cadaver showed that osteoarthritis is related to osseous outgrowths and osteophytes of the articular surface of the median atlanto-axial joint, presence of congenitally developed free ossicle and of third occipital condyles. Particles of these osteophytes were found usually on the superior rim of the anterior arch of the atlas, but in a few cases we also found it on the inferior rim. Some osteophytes were broken off and appeared as "free" ossicles that had sharp, cut margins.7) In our case, the plain X-ray, CT and MRI images showed no definite osteoarthritic change.

Second, calcific tendinitis of the longus colli muscle or stylohyoid ligament should be differentiated. Calcific tendinitis of the longus colli muscles is an result of inflammation is cause by deposition of calcium hydroxyapatite in the superior oblique tendon fibers of the longus colli muscles. The clinical symptom is nonspecific, from acute to subacute onset of neck pain, dysphagia or odynophagia, and low grade fever and without history of trauma.1, 8) Calcific tendinitis of stylohyoid ligaments is related to as Eagle's syndrome. Eagle's syndrome is defined as the symptomatic elongation of the styloid process or mineralization of the stylohyoid ligament complex. The symptom of calcified stylohyoid ligament is variant, from mild pain to acute neurologic referred pain and it would be confused with other cause of head and neck pain.9) The characteristic of radiographic findings of calcific tendinitis of longus colli are prevertebral soft tissue swelling and amorphous calcifications in the prevertebral old avulsion fracture or nonunion. Regarding the origin of the ossicle, sharp and irregular margins indicates nonunion of an avulsion fracture, while ossicle has a round or oval shape with a well defined cortical margin, it suggests it is congenital. However, it is sometimes difficult to find out the exact etiology because a long-standing avulsion fracture could have smooth margins. Avulsion fracture or nonunion is associated with a traumatic event. In this case, the patient had not any traumatic events before this trauma.

In this case, the authors suspected an anterior arch fracture of atlas due to traumatic event. To avoid make a misdiagnosis further image evaluation are essential, for instance CT, MRI, or scans. Even though it is hard to have an inferior accessory ossicle congenitally, and trauma history in the same time, surgeons must keep in mind that the inferior accessory ossicle of the anterior arch of the atlas could be misdiagnosed as anterior arch fracture.

References
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