The hypotympanum contains the opening to the eustachian tube, with the internal carotid artery seen along its medial margin ( Fig 4). The middle ear can be further subdivided into the epitympanum (attic) superior to the level of the tympanic membrane, mesotympanum at the level of tympanic membrane, and hypotympanum inferior to the level of tympanic membrane ( Fig 5). This space is marginated by the pars flaccida and scutum laterally, the lateral malleal ligament superiorly, and the neck of the malleus medially. Another important area of the middle ear is the Prussak space (superior recess) ( Fig 5). The pyramidal eminence overlies the stapedius muscle, which inserts onto the head of the stapes. The posterior wall of the middle ear cavity is irregular and includes the facial recess (also referred to as the facial nerve recess), pyramidal eminence, sinus tympani, and round window niche, from lateral to medial ( Fig 3). The tegmen tympani is the roof of the middle ear, and the tegmen mastoideum is the roof of the mastoid ( Figs 4, 5). The tegmen refers to a thin plate of bone that separates the dura of the middle cranial fossa from the middle ear and the mastoid cavity. The scutum is a sharp bony projection to which the tympanic membrane is attached superiorly ( Fig 5). The middle ear is an air-filled cavity within the petrous portion of the temporal bone that contains the ossicular chain and is bounded by the tympanic membrane laterally, the inner ear structures (surrounded by the otic capsule and the cochlear promontory) medially, the tegmen tympani superiorly, and the jugular wall (floor) inferiorly ( Fig 5). The major anatomic landmarks of the temporal bones are depicted on axial and coronal CT images ( Figs 1– 5) and are described in the following subsections.įigure 1: Axial CT image shows: 1, mastoid antrum 2, aditus ad antrum 3, epitympanum 4, lateral semicircular canal 5, vestibule 6, labyrinthine segment of the facial nerve 7, IAC 8, posterior semicircular canal. Several intrinsic channels, intrinsic fissures, and extrinsic sutures are often apparent on CT images and can mimic fractures (pseudofractures) ( 1). Each temporal bone is composed of five osseous parts: the squamous, mastoid, petrous, tympanic, and styloid portions. The temporal bones comprise the lateral skull base, forming portions of the middle and posterior fossae. It is helpful to examine the region in an organized and systematic fashion, going through the same checklist of key structures each time. There are a limited number of structures and disease entities in the temporal bone with which one must be familiar in order to proficiently interpret a computed tomographic (CT) or magnetic resonance (MR) imaging study of the temporal bone. For this journal-based CME activity, author disclosures are listed at the end of this article. The ACCME requires that the RSNA, as an accredited provider of CME, obtain signed disclosure statements from the authors, editors, and reviewers for this activity. Physicans should claim only the credit commensurate with the extent of their participation in the activity. The RSNA designates this journal-based activity for a maximum of 1.0 AMA PRA Category 1 Credit TM. The RSNA is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians. Distinguish between various tumors of the temporal bone based on CT and MR findings.Describe imaging features of some common inflammatory conditions in the temporal bone.Recognize clinical presentations associated with important inflammatory and neoplastic conditions in the temporal bone region. Identify important anatomic landmarks in the temporal bone.After reading the article and taking the test, the reader will be able to:
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