21 Bradley L. Njaa Kansas State University, USA The ear is three anatomically defined but interconnected portions: the external ear, the middle ear, and the internal ear. The external ear is derived from the embryonic ectoderm and mesenchyme of the first and second pharyngeal arches, responsible for the various portions of the pinna and the first pharyngeal cleft, which is the primordial external acoustic meatus (EAM).1 The EAM is the bony and cartilaginous tube commonly referred to as the external ear canal. It connects the external and middle ear. The middle ear is derived from the pharyngeal groove, becoming the tympanic cavity and auditory tube, as well as portions of the first and second pharyngeal arches that form the auditory ossicles and associated muscles and nerves. Apposition between the external pharyngeal cleft and internal pharyngeal groove result in formation of the tympanic membrane and associated supportive connective tissue.2 The internal ear is derived from the otic placode, which represents embryonal ectoderm that invaginates to form the otic vesicle and associated mesenchyme that differentiate into the petrous portion of the temporal bone and associated labyrinths.3 The internal ear is difficult to evaluate grossly or histologically because of its dense bony otic capsule, relatively small size, as well as challenges associated with processing and sectioning. Therefore, the incidence of internal ear neoplasia in animals may be underestimated. Neoplasms involving the internal ear include nerve sheath tumors of cranial nerves, primary intracranial tumors that compress cranial nerves, middle ear tumors that are destructive to the petrous portion of the temporal bone, and rarely metastatic tumors. In people, the only primary tumors arising from within the petrous portion of the temporal bone are endolymphatic sac tumors.4 The endolymphatic sac is a blind‐ended compartment in direct communication with the membranous labyrinth, responsible for regulating endolymph pressure, fluid volume, and ionic balance.5 Endolymphatic sac tumors are considered low‐grade papillary adenocarcinomas that are variably cystic and have not yet been recognized in domestic animals. Clinical signs seen with tumors in the internal ear largely depend on which cranial nerves are infiltrated or compressed and include: circling, ataxia, head tilt, nystagmus, pain on opening the mouth, perceived or confirmed deafness, Horner syndrome, facial myokymia, facial nerve deficits, and possibly evidence of vagal, glossopharyngeal, hypoglossal, and trigeminal nerve deficits.6–10 Additionally, muscular control to open the auditory tube depends partially on normal trigeminal nerve function, therefore impaired trigeminal innervation can lead to middle ear effusion due to auditory tube dysfunction. Effusions in the middle ear are a fairly common clinical problem associated with a variety of internal and middle ear diseases. The more common signs related to intracranial neoplasia are referable to vestibular or auditory dysfunction and include seizures, blindness, depression, and aggression.6–9 Vestibular disease signs as well as presumed deafness may be related to local invasion of the vestibular and acoustic nuclei.11 In dogs and cats, meningiomas are the most commonly reported intracranial tumors that lead to signs of vestibular or auditory dysfunction.8,9,12 Rarely, meningiomas have been reported to extend into the internal acoustic meatus or adhered to the surface of the petrous portion of the temporal bone.11 These patients generally have a poor long‐term prognosis. The tumors are in the internal ear because they have infiltrated from a primary location in adjacent structures. Their location makes surgical removal difficult and some are primary brain tumors. In people, nerve sheath neoplasms account for 7–10% of all primary intracranial tumors. Nearly 90% involve the cerebellopontine angle and the majority are schwannomas of the vestibulocochlear nerve (cranial nerve (CN) VIII).13 They arise from the stromal matrix in CN VIII as oligodendrocytes transition to Schwann cells. This occurs as the nerve enters the internal acoustic meatus (IAM). The IAM is the bony foramen on the medial surface of the petrous portion of the temporal bone through which the CN VII and CN VIII exit the cranial cavity. The majority of nerve sheath neoplasms in the internal ear of dogs involve the trigeminal nerve.14 However, nerve sheath neoplasms originating from CN VIII are occasionally seen in dogs and cattle.13,15 Most nerve sheath tumors of CN VIII in slaughter cattle are considered benign based on the gross appearance of solitary expansile, non‐invasive tumors that lack histomorphologic features of malignancy. An “acoustic schwannoma” was reported in a dog.13 Neoplastic cells had moderate pleomorphism, there were 6 mitoses/10 HPF, and the tumor was not invasive but was considered malignant. Trigeminal nerve sheath tumors may impinge on CN VIII or CN VII in dogs and one is reported in a cow.16–18 An interesting side effect of neoplasia of the trigeminal nerve is the development of middle ear effusion as it relates to the specific function of one branch. The trigeminal nerve has three main branches: the ophthalmic branch (sensory to the eye and surrounding skin), the maxillary branch (sensory innervation of the maxillary area of the face), and the mandibular branch (motor innervation of the muscles of mastication and innervation to the tensor veli palatini muscle).17 The tensor veli palatini muscle is partially responsible for opening the auditory tube (eustachian tube). A statistically significant correlation was made between the presence and size of a tumor involving the trigeminal nerve and the degree of muscle atrophy of the masseter muscle and tensor veli palatini muscle based on MRI analysis. The severity of muscle loss correlated with the degree of middle ear effusion, as determined by MRI. This suggests an association between trigeminal nerve neoplasia, neurogenic atrophy of the tensor veli palatini muscle, auditory tube dysfunction, and middle ear effusion. Histologic features of these tumors are spindloid cells arranged into interlacing bundles that are variably interrupted by clefts that contain pale eosinophilic material. Neoplastic cells contain moderate amounts of fibrillar, eosinophilic cytoplasm with oval to elongate nuclei with stippled chromatin and generally 1–2 nucleoli. Anisokarayosis and pleomorphism are variable but tend to be moderate in tumors considered malignant. Mitotic figures tend to be rare in benign tumors but numerous in malignancies. Multicentric nerve sheath tumor affecting the 4th or 5th through the 8th cranial nerves has been reported in two dogs.19 Clinical signs corresponded to the various cranial nerves infiltrated. In both cases, the neoplastic cells were anaplastic spindloid cells arranged in solid sheets, broad bands or whorls with large, vesicular to elongated nuclei with a single indistinct nucleolus. Moderate numbers of mitotic figures were observed. Collagenous deposition varied from moderate to severe with moderate vascularization. Neoplastic cells did not depict S100 positivity. Therefore, both were classified as malignant nerve sheath sarcoma. A single case report documented lymphoma in several cranial nerves in an 8‐year‐old, male Persian cat.20 Clinical features included left‐sided head tilt, slight ataxia, facial paralysis, and bilateral otitis externa. Imaging of the bullae confirmed middle ear effusion and autopsy examination confirmed a suppurative otitis media. Lymphoma was present in several left cranial nerves, including trigeminal, abducens, oculomotor, facial, and vestibulocochlear cranial nerves. Squamous cell carcinoma may infiltrate the internal ear from origins in the external acoustic meatus, oral cavity, or nasopharynx.21 Bony erosion of the tympanic bulla and petrous portion of the temporal bone by the tumor will eventually lead to vestibular signs and possible invasion into the cranial cavity or brainstem. Squamous cell carcinoma has also spread from the pinna to the external acoustic meatus and the meninges resulting in “meningeal carcinomatosis” in two cats.22 Both cats had previously undergone bilateral total ablation of the pinnae and both cats exhibited ataxia, circling, and altered behavior. Gross evidence of neoplasia was absent in the middle ear. The authors speculated this was due to hematogenous spread; however, a more plausible mechanism is extension along cranial nerves, such as the facial nerve. In both cats, neither the middle nor internal ears were examined histologically in order to confirm or deny this pathogenesis. The middle ear is normally an air‐filled cavity that extends rostrally to the nasopharynx through the auditory tube (eustachian tube), laterally to include the internal edge of the tympanic membrane and associated auditory ossicles (malleus, incus, and stapes), dorsally into the epitympanic recess, and ventrally and caudally into the tympanic bulla. The dorsomedial wall of the middle ear is the ventrolateral surface of the petrous portion of the temporal bone. The middle ear and auditory tube are evaginations off the nasopharynx and therefore share a similar mucosal epithelium comprising ciliated, pseudostratified epithelial cells mixed with goblet cells.1–5 In horses, the auditory tube diverticulum or guttural pouch is similarly lined.6 However, there are portions of the middle ear and guttural pouches that are lined by non‐ciliated, cuboidal to squamous epithelium.6,7 Most of the middle ear mucosa is an amalgam of lining epithelium and propria submucosa fused with the soft tissue periosteum of the surrounding bony capsule and is referred to as the mucoperiosteum4,5,8 (Figure 21.1). Figure 21.1 Cat mucoperiosteum, middle ear. Mucoperiosteum is a layer of tissue composed of the surface epithelium, loose connective tissue of the propria submucosa and periosteum of bone found in the middle ear. Ciliated, columnar epithelium mixed with goblet cells is contiguous with respiratory epithelium in the nasopharynx and gradually transitions to flattened epithelium. If this epithelium invaginates the structures formed are lined by epithelium and are referred to as “pseudoglands.” Controversy exists in the literature as to whether there are glands in the mucoperiosteum; however, this author has observed them at the junction of the rostral middle ear and auditory tube in dogs and in cats and they are documented in the propria submucosa of the guttural pouch (M.M. Sula and B.L. Njaa, personal communication).6 These glands are lined by goblet cells and are very uniform. They must be differentiated from pseudoglands, which are found in the mucoperiosteum associated with otitis and that originate as folds that form in the inflamed mucoperiosteum. The pseudoglands are variable in diameter and have epithelial lining that ranges from attenuated mucosa to ciliated cuboidal to columnar epithelium mixed with goblet cells. Because these form during middle ear inflammation, they frequently contain or are infiltrated by neutrophils. Tumors of the middle ear are uncommon in dogs and cats and rarely diagnosed in other domestic species. Non‐neoplastic masses in the middle ear represent a broad category that includes aural inflammatory polyps (common in cats uncommon in dogs); tympanokeratoma (cholesteatoma) (dogs only); cholesterol granulomas (dogs and cats); and mucoperiosteal exostoses (dogs and wild cats only). Given the middle ear cellular ontogeny, neoplasms are generally derived from the lining epithelium and most neoplasms are malignant based on histomorphologic features. The epithelial tumors include papillary adenomas, adenocarcinomas, and squamous cell carcinomas. Rare instances of mesenchymal neoplasms are also reported, either as primary or metastatic neoplasms. Middle ear neoplasia in dogs often manifests as otalgia (ear pain) and otomiasma (miasmic or foul‐smelling otorrhea). In cats, middle ear neoplasia similarly depicts otalgia and otomiasma but additionally may depict signs of Horner syndrome, vestibular signs (head tilt, ataxia) or facial nerve paralysis, or in combination. Another sign in dogs and cats is pain associated with opening the mouth. Neoplasia confined to the middle ear may remain as an occult disease or manifest signs consistent for otitis externa or cranial nerve deficits. Facial nerve paralysis alone may be the only evidence of neoplasia. Any involvement of the CN VIII supports internal ear involvement. Surgical intervention of middle ear or guttural pouch neoplasia has a uniformly poor prognosis. Benign epithelial tumors arising in the middle ear are rare or are rarely diagnosed.9–11 The first documented case was in a 9‐year‐old beagle that was part of a colony of 534 beagles. They were in an experimental trial and all underwent a complete autopsy. This bitch had a 9‐month history of left‐sided head tilt. The mass was light‐colored, semi‐firm, and filled the middle ear. There were papillary projections composed of layers of cuboidal to columnar, ciliated, pseudostratified epithelium interspersed with goblet cells. The diagnosis was a papillary adenoma originating from the epithelium lining the auditory tube. Papillary adenomas were also reported in two older dogs.10 One adenoma was thought to originate from the mucosa of the middle ear, and in one case it appeared to arise from the mucosa lining the tympanic membrane. This is rarely observed in clinical material submitted for histologic evaluation (Figure 21.2). Figure 21.2 Dog papillary adenoma middle ear. Neoplastic cells are bland cuboidal cells that line papillary fronds with a thin, central fibrovascular core. A papillary adenoma was reported in a 15‐year‐old cat with persistent right‐sided head tilt and persistent otitis externa.11 The middle ear contained a mass that was composed of papillary fronds lined by well‐differentiated epithelium. Mitotic activity was not mentioned and there was no evidence of vascular or lymphatic invasion. Malignant epithelial neoplasms involving the middle ear are more likely than benign neoplasms but are still considered uncommon. They include squamous cell carcinoma, adenosquamous carcinoma (Figure 21.3), and carcinoma of undetermined origin. Given the heterogeneous epithelium of the mucoperiosteum, neoplastic transformation of this epithelium is the likely genesis of these neoplasms although extension from the external acoustic meatus, guttural pouch, or oral cavity into the middle ear are also possible sources. Figure 21.3 Cat carcinoma middle ear. Neoplastic epithelium that forms small acini as well as squamous epithelial pearls (arrow) proliferate along the surface of the mucoperiosteum. These neoplastic cells are moderately pleomorphic, mitotic figures were seen at higher magnifications. Several invaginated pseudoglands (P) are present within the propria submucosa of the mucoperiosteum. Plasma cells and lymphocytes infiltrate as well as form lymphoid follicles (base of image). Squamous cell carcinoma (SCC) is the most common middle ear malignancy in cats.12–17 Most of the cats with middle ear SCC are older than 10 and rarely less than 6 years old. Signs include otomiasma, pruritis, facial nerve paralysis, ataxia, Horner syndrome, depression, pain when opening the mouth, and head tilt and circling toward the affected side. Middle ear SCC was also reported in an 8‐year‐old golden retriever.18 Pain could be elicited when opening the mouth as well as from palpation of the region of the tympanic bulla and temporomandibular joint. Bony lysis was evident in the left tympanic bulla and the tympanic membrane was ruptured. The majority of the mass was debulked and despite adjunctive radiation therapy, the dog developed pulmonary metastasis and was euthanized. Additional tumors reported include adenocarcinomas in cats13,19 and a dog.10 These tumors had glandular and squamous cell proliferation and were designated as adenocarcinoma of unknown origin or adenosquamous carcinoma. An anaplastic tumor was in the middle ear of a 3‐year‐old border collie.10 An autopsy confirmed neoplasia in the oropharynx, nasopharynx, right middle ear, and external acoustic meatus. Metastatic nodules were present in the lung. The site of origin and definitive cellular lineage was never determined through the use of histochemical and immunohistochemical (IHC) stains. Regardless of histologic designation, carcinoma in the middle ear has a poor long‐term prognosis due to the expansile and infiltrative growth into the internal ear and other adjacent structures as well as metastasis to lymph nodes or lungs. Surgical removal of the tumor is often a debulking, palliative procedure. Horses have one of the longest auditory tubes (eustachian tube; pharyngotympanic tube) and they also have bilateral, multi‐chambered, air‐filled, thin‐walled auditory tube diverticula or guttural pouches.1 Guttural pouches have lateral and medial compartments that straddle the stylohyoid bone and, ventrally, left and right medial pouches are apposed, forming a thin median septum. These pouches bilaterally occupy the space that extends from the base of the skull to the atlas dorsally and extend to the proximal origin of the esophagus ventrally. The mucosal lining is contiguous with the epithelium lining the auditory tube and nasopharynx and is composed of ciliated, pseudostratified epithelium mixed with goblet cells. The middle ear is lined similarly. The first pharyngeal pouch is the embryonic endodermal evagination of the pharynx that expands centrifugally between the first and second branchial or pharyngeal arches to form the auditory tube, the tympanic cavity, and the associated lining mucosa. Retention of remnants of the first pouch can potentially result in the formation of cysts. These cysts are sometimes referred to as branchial cysts. Guttural pouch cysts have been reported in two horses.2 Both involved the medial and lateral compartments and responded well to fenestration and removal of portions of the cyst epithelium. The youngest was a 1‐month‐old Quarter Horse with a cyst involving the right guttural pouch. Histological features included minimal mixed inflammation and a generally intact pseudostratified columnar epithelium with few areas of ulceration. The second case was in a 3‐year‐old Standardbred that had raced successfully but developed progressive, severe dyspnea with inspiratory and expiratory noise. The cyst was ulcerated; it contained mild neutrophilic inflammation, and hemorrhage and granulation tissue at the periphery. There are few reports of neoplasia originating in the guttural pouch.3–11 In general, affected horses are 10 years old or more. Initial clinical symptoms include pharyngeal swelling, often bilateral malodorous nasal discharge, epistaxis, coughing, dyspnea, head tilt to the side of affected guttural pouch, and various cranial nerve deficits. Masses are typically unilateral and rarely bilateral. Neoplasms are almost always SCC that tend to metastasize to the retropharyngeal lymph node and rarely to the lung.5,6 Few reports document extension from the guttural pouch to the tympanic cavity or extension from the external and tympanic cavity to the guttural pouch. Benign guttural pouch neoplasms have been reported in two horses. A pedunculated and obstructive fibroma was partially removed from the left guttural pouch of a 13‐year‐old Quarter Horse with deficits involving cranial nerves IX, X, XI, and the sympathetic trunk.10 Histologic examination diagnosed a fibroma with confirmed mature connective tissue that had undergone myxomatous degeneration. This tissue was overlaid by the mucous membrane typical of the guttural pouch. The second example was an encapasulated, centrally friable and hemorrhagic mass that was suspended from the roof of the medial compartment of the left guttural pouch.11 The diagnosis was hemangioma and it was described as a mass of endothelial cells with an anaplastic appearance but few mitotic figures. By a wide margin, the most common guttural pouch tumor is SCC.3–9 Most of the cases diagnosed are unilateral with a single case of bilateral SCC that originated as an external and middle neoplasm. Grossly, these tumors tend to be ulcerated, hemorrhagic and locally invasive. Histologic features are typical for SCC, including keratin pearls in primary and metastatic lesions as well as desmoplasia. In all cases, affected horses died or were euthanized. Other malignant tumors reported in the guttural pouch include cases of hemangiosarcoma, metastatic melanoma, and a round cell sarcoma.8 Lymphoma of the middle ear has been reported in cats, and a dog.1–4 Morphologic features described are typical for lymphoma and include abundant, discrete, round cells that looked lymphoblastic. One of the cats presented with right‐sided deficits including head tilt, circling to the right, right facial paralysis as well as Horner syndrome of the right eye.3 Surgical intervention confirmed soft tissue mass in the medial and lateral middle compartments separated by the septum bullae with enlargement of the right submandibular lymph node. A large‐cell, CD3‐positive, T‐cell lymphoma was confirmed in the bulla and lymph node of this cat.3 The dog was a 3‐year‐old shih tzu with head tilt, ataxia, seizures, and lymphocytic pleocytosis in the CSF diagnosed as a B‐cell lymphoma.4 The lymphoma was in the retropharyngeal lymph nodes and soft tissue present in the bullae. Nasopharyngeal lymphoma was determined to be the most common neoplasm in cats associated with effusion in the middle ear.5 Approximately 46% of cats had sinonasal neoplasia and 16/21 (76%) were diagnosed as lymphoma. This may cause auditory tube dysfunction. Paraganglia are broadly categorized as adrenal or extra‐adrenal, each displaying roughly symmetric distribution.6 Paraganglia germain to the ear include parasympathetic paraganglia found in the glossopharyngeal and vagal nerves. Glossopharyngeal paraganglia include the tympanic branch paraganglia located within the mucoperiosteum of the middle ear. Vagal branches innervate the jugular paraganglia located adjacent to the middle ear along the medial surface of the bullae within the jugular foramen. Ear‐associated paraganglia are deemed jugulotympanic (tympanojugulare) and vagal paraganglia. These tumors have been erroneously diagnosed as glomus jugulare tumors.7 Ear‐associated paragangliomas are extremely rare and only reported in dogs.7–11 Based on the few published reports and inferences made from case series of carotid body tumors in which the ear was involved,10–14 these tumors seem more common in young male dogs. Clinical signs include head tilt toward the affected side, facial nerve paralysis, Horner syndrome, and cranial nerve signs. In people, these are relatively common tumors and typically are benign. In dogs, the tumors are large at the time of diagnosis and it is difficult to determine if they arise in the jugulotympanic or vagal paraganglia. Middle ear paragangliomas are expansile and may result in bony lysis of the tympanic bullae, petrous portion of the temporal bone, auditory ossicles or a combination of all (Figure 21.4). As they expand, they may extend into the external acoustic meatus, through the auditory tube into the nasopharynx or extend into the petrous portions of the temporal bone and into the cranial cavity. Distant metastasis has been reported in a few cases as well as extension into the brain. Effusion is not a reported feature of these tumors. Figure 21.4 Dog jugulotympanic paraganglioma middle ear. (A) Ventral view of the skull with the tympanic bullae opened and the paraganglioma filling the left tympanic bulla. Mucoperiosteal exostoses are visible in the right tympanic bulla. (B) Low magnification of the tumor partially filling the middle ear (M), eroding the petrous portion of the temporal bone (P) and extending into the cranial cavity (C). The utriculus (U) is visible in the internal ear. (C) High magnification of neoplastic cells with cytoplasmic granules and moderate anisokaryosis as well as occasional mitotic figures. (D) Grimelius stain confirming agyrophilic cytoplasmic granules. (C,D, Images courtesy of Jim Cooley, Mississippi State University.) (A,B, Source: Cooley et al. (1990).9 Reproduced with permission of Elsevier.) These tumors are tan to red, modestly firm, and highly vascular. Finger‐like tumor processes extend into lytic bone of tympanic bullae (Figure 21.4B). All accounts to date have documented unilateral disease. Histologically, the neoplastic cells are small, uniform, polyhedral to cuboidal, and contain granular cytoplasm (Figure 21.4C). Nuclei are small, round, and uniform, with euchromatic to finely stippled chromatin. Tumors form small nests, clusters, or broader sheets subdivided by thin bands of fibrovascular stroma. Frequently, anastomosing cords of cells cluster around the abundant tumoral blood vessels. Most tumors contain numerous vascular channels, and mitotic counts are highly variable ranging from rare to up to 6 mitoses per HPF.8,9 Metastasis has been reported in a few cases.8,9 Grimelius stain is useful to visualize the characteristic intracytoplasmic granules (Figure 21.4D). IHC stains that have proven useful for these masses include positive staining with synaptophysin, neuron‐specific enolase, and PGP9.5.6 Fibroma,15 fibrosarcoma,16 sarcoma,17 osteosarcoma,17 and melanoma18 are reported, but all of these common tumors are rarely found in the middle ear. These neoplasms may extend from the external acoustic meatus into the middle ear15,18 or originate within the middle ear.16–18 Lysis of the petrous portion of the temporal bone, tympanic bulla bone, and compression or destruction of the facial nerve is reported. Vestibular signs are most commonly associated with these tumors.
Tumors of the Ear
General considerations
INTERNAL EAR
Clinical characteristics
Tumors
References
MIDDLE EAR
Clinical characteristics
Prognosis
Epithelial tumors
Papillary adenoma
Carcinomas
References
Guttural pouch
Guttural pouch cysts
Guttural pouch neoplasia
References
Non‐epithelial tumors
Lymphoma
Jugulotympanic paraganglioma
Mesenchymal tumors
References
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