The Ear
Peter A. Humphrey
Rebecca D. Chernock
I. NORMAL ANATOMY. The ear is composed of the external ear, the middle ear, and the inner ear. The external ear is made up of the auricle, which leads to the external auditory canal. The auricle has a supporting plate of elastic cartilage, which also helps form the outer two-thirds of the external auditory canal. Skin covers both the auricle and the canal; the main distinctive histologic features of this skin are that the squamous lining of the inner half of the canal is thinned, and that modified apocrine glands called ceruminal glands are present in the outer third of the canal. The clustered ceruminal glands are lined by cuboidal epithelial cells that have an eosinophilic cytoplasm that often harbors a granular golden-yellow pigment (e-Fig. 7.1).*
The middle ear, or tympanic cavity, lies within the temporal bone. It is separated from the external auditory canal by the tympanic membrane, a thin fibrous sheet that has an external keratinizing squamous epithelial lining and an inner cuboidal cell lining. The middle ear contains the three auditory ossicles (malleus, incus, and stapes), ossicle ligaments, tendons of the ossicular muscles, the auditory tube, the tympanic cavity itself, and the epitympanic recess, the mastoid cavity, and the chorda tympani of the facial nerve (cranial nerve VII). The auditory or eustachian tube connects the tympanic cavity with the nasopharynx. The tympanic cavity is lined by a single layer of flattened to cuboidal respiratory epithelium, whereas most of the auditory tube is lined by low ciliated epithelium.
The inner ear is located within the petrous portion of the temporal bone and is composed of a membranous labyrinth surrounded by an osseous labyrinth. The membranous labyrinth houses the cochlea and the vestibular apparatus, both of which are supplied by cranial nerve VIII. There are several parts to the cochlea: the cochlear duct with the organ of Corti (the end organ of hearing), and the scala vestibuli and scala tympani, which hold the perilymph. The organ of Corti has thousands of neurotransmitting hair cells. The vestibular apparatus, which functions in motion and position sensing, consists of three semicircular canals and the utricle and the saccule. The ampullae of the canals have a sensory end organ, the crista ampullaris, with neurosensory hair cells. The utricle and the saccule also possess a sensory end organ, the macula, which has neurosensory hair cells and otoliths. There is also a blind sac in the membranous labyrinth known as the endolymphatic sac, which is lined by tall columnar epithelium arranged on papillae.
II. GROSS EXAMINATION AND TISSUE SAMPLING
A. External ear. Biopsy and excision specimens should be handled as skin specimens from other anatomic sites (see Chaps. 38, 39 and 40).
B. Middle and inner ear. Samples from the middle ear are often obtained in cases of suspected cholesteatoma. For these cases, it should be noted whether bone fragments are present. Standard hematoxylin and eosin (H&E) slide preparation is sufficient. Ossicles from the middle ear can be processed by gross examination only unless microscopic examination is requested by the surgeon. For middle ear and inner ear neoplasms, which are uncommon, use of ink to mark the peripheral margins is not usually necessary because these specimens are typically received as small fragments. In those rare cases in which the patient has a history of
lymphoma or lymphoma is suspected clinically, fresh tissue should be processed according to the standard lymphoma work-up protocol. For all other middle ear samples, all tissue should be submitted for histologic examination, with H&E slide generation.
III. COMMON DISEASES OF THE EXTERNAL EAR
A. Nonneoplastic diseases. The common diseases of skin that involve the pinna and the external ear canal are covered in the chapters on skin (Chaps. 38, 39 and 40). Some diseases have a particular predilection for the skin of the ear, including gout, keloids (often secondary to ear piercing), relapsing polychondritis, angiolymphoid hyperplasia with eosinophilia (epithelioid or histiocytoid hemangioma), and chondrodermatitis nodularis (the latter is discussed below).
1. Congenital anomalies of the ear that may be seen by the surgical pathologist include accessory tragi, branchial cleft abnormalities, congenital aural sinuses, and salivary gland ectopia.
a. Accessory tragi are found at birth and clinically and macroscopically are most often solitary, sessile, or pedunculated polyps in the preauricular area. Microscopically, skin, hair follicles, and a central fibrofatty core with or without cartilage are observed (e-Fig. 7.2). They should not be misdiagnosed as a papilloma, fibroma, or chondroma.
b. Anomalies of the first branchial cleft present near the ear as cysts, sinuses, and fistulas. The epithelial lining can be squamous or respiratory; type I or pure squamous cell-lined cysts can be confused with keratinous cysts histologically. Lymphoid tissue in the wall (e-Fig. 7.3) is less frequently found in the first branchial cleft cysts than in the much more common second branchial cleft cysts, which arise in the lateral neck. Type II defects can harbor skin including adnexal structures or cartilage (e-Fig. 7.4); associated salivary gland tissue may also be present when the process extends into or near the parotid gland.
c. Congenital aural sinuses are distinguished from branchial cleft anomalies by location: Branchial cleft abnormalities are found in infra- or postauricular sites, whereas congenital aural sinuses are present in a preauricular location.
2. Chondrodermatitis nodularis helicis is a condition of uncertain etiology that occurs on the skin of the external ear, usually on the upper part of the helix. Clinically, middle-aged or older, typically male, patients present with a small (<1 cm) painful nodule that can be ulcerated and can exhibit a crust. This appearance can clinically simulate actinic keratosis or squamous cell carcinoma. Microscopically, there is a somewhat funnel-shaped ulcer with associated dermal collagen edema and degeneration. There may be surrounding pseudoepitheliomatous squamous cell hyperplasia (e-Fig. 7.5), granulation tissue and fibrosis, and a predominantly lymphocytic inflammatory cell infiltrate, although the infiltrate can be mixed. A perichondritis with destruction of cartilage can be seen but is uncommon. Superficial or shave biopsies may show only a few of the above findings. Curettage and cautery are used for treatment, with recurrence in a minority of patients.
3. Otitis externa is inflammation of the external auditory canal and/or pinna and is very common in clinical practice. Biopsy is generally not indicated.
4. Necrotizing (malignant) otitis externa is usually caused by Pseudomonas aeruginosa infecting diabetic patients, but fungi can also be the causative agent. Microscopically, the response is one of necrotizing inflammation.
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