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Published on: March 7, 2014
Characterization of middle ear ossicular ligaments using photon counting detector CT
Dinesh Rao1, Richard D Beegle1, Jeet Patel1
1Department of Radiology, Mayo Clinic, 4500 San Pablo Blvd, Jacksonville, FL 32224, USA.
Background And Purpose:
The middle ear suspensory ossicular ligaments have been previously described on traditional energy integrating detector CT scanners. With recent developments in photon counting detector CT, these ligaments can be better visualized due to greater spatial and contrast resolution.
Materials And Methods:
50 patients (100 temporalbones) without hearing loss or middle ear cavity pathology were retrospectively reviewed to characterize the middle ear suspensory ossicular ligaments including the anterior, superior, lateral mallear, and posterior incudal ligaments, and stapes and tensor tympani tendons. Structures were classified as: 0 - not visualized, 1 - thin, 2 - thick, 3 - calcified, 4 - bar. Interrater agreement statistics and associated significance levels are reported.
Results:
The anterior and superior mallear ligaments have more complex anatomy and variability than what has been published previously in the radiology literature. The anterior mallear ligament forms a complex with the chorda tympani and the discomallelar and sphenomandibular ligaments. An accessory superior anterior mallear ligament was observed in 67 of 100 subjects. Variant anterior and posterior superior mallear ligaments were observed in 28 and 38 temporal bones, respectively. The posterior incudal ligament was virtually always present and thick, while the lateral mallear ligament was present and thin. The stapes tendon was usually thin, while the tensor tympani tendon was thick. Calcified ligaments and bars were observed in a minority of the ligaments.
Conclusions:
Photon counting CT allows for characterization of the ossicular ligaments which is qualitatively consistent with anatomic studies that demonstrate greater complexity than what has been described in the radiology literature.
Clinical Impact:
Radiologists and otologists must recognize the increased complexity and variability of middle ear ligaments when using photon counting CT, particularly as it becomes more widely adopted and is suited for imaging of the temporal bone. The findings presented in this manuscript allow for recognition of this anatomy which can facilitate image interpretation.
Abbreviations:
AML: anterior mallear ligament; S-AML, superior anterior mallear ligament; M-AML, middle anterior mallear ligament; CHL, conductive hearing loss; ChT, chorda tympani; DML, discomallelear ligament; EID-CT, energy Integrated Detector CT; I, Incus; M, Malleus; LML, lateral mallear ligament; MEC: middle ear cavity; PCCT, photon counting detector CT; PIL, posterior incudal ligament; PTF, petrotympanic fissure; SML, superior mallear ligament; SpML, sphenomandibular ligament; A-SML, anterior superior mallear ligament; P-AML, posterior superior mallear ligament; SNHL, sensorineural hearing loss; ST, stapedius tendon; TTT, tensor tympani tendon.
