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|LETTER TO EDITOR
|Year : 2016 | Volume
| Issue : 5 | Page : 1074-1075
“Waning crescent moon” - A new sign or an imaging artifact
Ambati Sumanth Kumar, Rajesh Alugolu
Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
|Date of Web Publication||12-Sep-2016|
Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kumar AS, Alugolu R. “Waning crescent moon” - A new sign or an imaging artifact. Neurol India 2016;64:1074-5
Ossification of the cervical ligamentum flavum (LF) is quite rare as frequent flexion-extension movements enable the LF to be in a lax state and thus maintain its elastic fibres. However, various patterns of the ossifications have been described. We, in this report, present a rare pattern of LF ossification. To the best of our knowledge, this pattern of LF ossification is the first of its kind reported in literature.
A 40-year old man presented with features of cervical compressive myelopathy. Magnetic resonance imaging of the cervical spine showed compression at the D2-3 level with type 1 myelomalacia. On computed tomography of the cervical spine, an ossified posterior longitudinal ligament was noticed at the cervical (C) 2-4 levels and a thick ossified ligamentum flavum (OLF) at the dorsal (D) 2-3 level [Figure 1]a. In the axial sections at C6 -7 levels, a hyperdense shadow was noticed which extended from the facet joint on one side until the opposite facet joint [Figure 1]b with inset]. On reviewing the sagittal images, it was found that the C6-7 space was, in fact, indistinguishable with the C7 lamina under-riding the C6 lamina, and the section was taken across the disc space.
|Figure 1: CT scan (a) Mid-sagittal section of the cervico-dorsal region showing the ossified posterior longitudinal ligament at the C2-4 levels and the ossified ligamentum flavum at the C6-7 and D2-3 levels. (b) Axial section at the C6-7 disc space showing a hyperdense ring extending from one facet to the other, resembling a “waning crescent moon” (inset)|
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Sato et al., have classified OLF according to the progression of the LF ossification into five types (Lateral, Extended, Enlarged, Fused and Tuberous)., Dong et al., have described the “comma sign” and “tram track” sign for diagnosing dural ossification on a computed tomographic scan.
The extension of the calcification from one facet across to the other facet in the presence of disorders of ligamental ossification leads us to propose a feature “the waning crescent moon sign” to describe this entity. The excessive lordosis and uniform calcification of the contiguous vertebrae may often prevent this radiological feature from becoming evident. On identifying such a pattern, however, the surgeon should be ready to decompress the cord using only a high speed drill, till the laminae are paper-thin.
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Singhal U, Jain M, Jaiswal AK, Behari S. Unilateral ossified ligamentum flavum in the high cervical spine causing myelopathy. Indian J Orthop 2009;43:305-8.
Sato T, Tanaka Y, Aizawa T, Koizumi Y, Kokubun S. Surgical treatment for ossification of ligamentum flavum in the thoracic spine and its complications. Spine Spinal Cord 1998;11:505-10.
Ahn DK, Lee S, Moon SH, Boo KH, Chang BK, Lee JI. Ossification of the ligamentum flavum. Asian Spine J 2014;8:89-96.