Barbara A. Bohne, Ph.D.
Gary W. Harding, M.S.E.
Dept. of Otolaryngology, Washington University School of Medicine, St. Louis, MO

Detailed knowledge of the microscopic anatomy of the human temporal bone is very useful for understanding surgical relationships and for interpreting radiological images of the temporal bone in patients with otologic problems. Preparation of the human temporal bone for microscopic study generally involves fixation, decalcification, embedding in a supporting medium such as celloidin and sectioning parallel to the long axis of the specimen at a thickness of 20 um. Initially every tenth section is stained and mounted for microscopic examination. The intervening sections are saved in 80% ethanol for future studies (e.g., immunocytochemical staining, DNA analysis, scanning electron microscopy).

This is section 200 (see below for legend) which passes through the approximate middle of the right temporal bone. It is shown here for orientation purposes: anterior - left edge; lateral - top edge; posterior - right edge; medial - bottom edge. This section contains most of the important structures in the middle and inner ears. After becoming familiar with the section orientation, a series of sections can be examined in order from the superior to the inferior surface of the temporal bone to identify the ossicles (malleus, incus and stapes); the course of the facial nerve; middle ear muscles (tensor tympani and stapedius); the 2 sensory regions in the vestibule (utricular and saccular maculae), the 3 sensory regions (cristae) of the semicircular canals; the organ of Corti in the cochlea; the endolymphatic duct and sac; and the round and oval windows. Higher power photomicrographs of certain key structures are also available by clicking on the link(s) in the figure legends.

In most cases, specific structures are labeled in the section(s) in which they appear most prominently but not in all sections. However, the facial nerve is labeled in every section in which it appears so it can serve as a landmark. In order to identify an unlabeled structure, the viewer should follow it through the sections until it becomes more prominent.

Dr. Gershon J. Spector graciously supplied the excellent slides from which the following images were obtained. The slides were acquired by Dr. Spector when he was a resident with Dr. H.F. Schuknecht, Massachusetts Eye and Ear nfirmary. We are grateful for the critical review of this document and many helpful suggestions, especially surgical perspectives, provided by Dr. J. Gail Neely.

Human Temporal Bone - A good overview of the middle and inner ears can be obtained by observing a human temporal bone from its superior surface after the tegmen tympani has been removed.

Section 1 - Epitympanic recess with body of incus; superior semicircular canal, scutum, aditis ad antrum.
Section 21 - Superior and lateral semicircular canals; geniculate ganglion of the facial nerve.
Section 41 - Ampullae of superior and lateral semicircular canals.
Section 61 - Beginning of tympanic segment of facial nerve; head of malleus and body of incus.
Section 81 - Chorda tympani near petrotympanic fissure; Körner's septum; beginning of cochlea.
Section 101 - Internal auditory meatus; beginning of utricle.
Section 141 - Tendon of tensor tympani inserting into the manubrium of malleus; chorda tympani passing medial to the malleus and lateral to the incus.
Section 161 - Mesotympanum; utricular macula; tensor tympani muscle.
Section 181 - Footplate of stapes fitted into oval window; origin of endolymphatic duct.
Section 200 - Modiolus of cochlea.
Section 221 - Anterior crus and posterior crus of stapes; lenticular process of incus; Eustachian (auditory) tube.
Section 241 - Tendon of stapedius muscle inserting into stapes head; internal carotid artery in carotid canal.
Section 281 - Endolymphatic sac gains access to posterior cranial fossa; operculum.
Section 300 - Hook portion of cochlear duct; promontory.
Section 321 - Round window membrane; crista of posterior semicircular canal.
Section 341 - Niche of round window.
Section 361 - Innervation of stapedius muscle by branch of facial nerve.
Section 381 - End of posterior semicircular canal.
Section 401 - Near end of basal turn of cochlea.

The human temporal bone can be sectioned sagitally, perpendicular to its long axis. Some structures are easier to follow in these vertical sections. The following series of sections are from a right temporal bone sectioned from postero-laterally to antero-medially. Orientation: Because the long axis of the temporal bone is 45° to the midsagittal plane of the skull, true medial is deep into the screen (or page) and true lateral is out towards the viewer. However, medial and lateral are used here to indicate general direction. Medial - left edge; superior - top edge; lateral - right edge; inferior - bottom edge.

Section 190 - Mastoid segment of facial nerve; chorda tympani; posterior and lateral semicircular canals.
Section 230 - Short process of incus.
Section 250 - Pyramidal bend of facial nerve; stapedius muscle.
Section 309 - Body of incus; endolymphatic duct.
Section 422 - Superior semicircular canal; tympanic membrane.
Section 459 - Cristae of lateral and posterior semicircular canals; malleus and incus; stapes head.
Section 480 - Ampulla of lateral semicircular canal; stapes footplate; lenticular process of incus.
Section 532 - Utricular macula; RW membrane; promontory.
Section 601 - Hook portion of the cochlear duct; tendon of tensor tympani muscle; origin of cochlear aqueduct from scala tympani in basal turn.
Section 691 - Beginning of basal turn of cochlea; internal auditory meatus.
Section 742 - Geniculate ganglion and labyrinthine segment of facial nerve.
Section 781 - Beginning of modiolus; tensor tympani muscle.
Section 841 - Mid-modiolar cut through cochlea.
Section 940 - Basal turn of cochlea tensor tympani muscle; auditory tube.

Copyright © 1997, Barbara A. Bohne and Gary W. Harding

Last updated 7/21/99

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