Biology:Omega sign
The omega sign, also called the hand knob, is the appearance on axial magnetic resonance imaging of the brain of a knob-shaped part of the precentral gyrus that bulges backward into the central sulcus and resembles the Greek letter omega (Ω).[1] The structure marks the motor area for the hand within the primary motor cortex, and it is used as a landmark to identify the precentral gyrus and the central sulcus on imaging.[1]
On axial images the central sulcus has an S-shaped course with three bends, or genua: superior, middle and inferior. The middle genu is the deepest and is concave toward the front, and the knob of cortex lying in front of it produces the omega shape.[2] The same knob looks like the letter epsilon (ε) in some people and like a hook on sagittal images.[1] It corresponds to the "middle knee" of the central sulcus described by anatomists in the 19th century.[1]
The omega sign is present in both cerebral hemispheres at roughly the same level, and the side opposite a lesion (the contralateral omega) can be used to work out where a lesion sits in relation to the central sulcus.[2][3] The landmark was described by Tarek Yousry and colleagues in 1997 using functional magnetic resonance imaging, which showed that hand movement activated this part of the precentral gyrus.[1]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Yousry, T. A.; Schmid, U. D.; Alkadhi, H.; Schmidt, D.; Peraud, A.; Buettner, A.; Winkler, P. (1997). "Localization of the motor hand area to a knob on the precentral gyrus. A new landmark". Brain 120 (1): 141–157. doi:10.1093/brain/120.1.141. PMID 9055804.
- ↑ 2.0 2.1 Kizilca, Ö.; Öztek, A.; Kesimal, U.; Şenol, U. (2017). "Signs in neuroradiology: a pictorial review". Korean Journal of Radiology 18 (6): 992–1004. doi:10.3348/kjr.2017.18.6.992. PMID 29089832.
- ↑ Campero, A.; Ajler, P.; Martins, C.; Emmerich, J.; de Alencastro, L. F.; Rhoton, A. (2011). "Usefulness of the contralateral omega sign for the topographic location of lesions in and around the central sulcus". Surgical Neurology International 2: 164. doi:10.4103/2152-7806.89892. PMID 22140649.
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