Benign lesions of the middle ear comprise a diverse spectrum of local and systemic diseases that have manifestations within the temporal bone. Despite their benign histopathological characteristics, these lesions may be locally destructive. Prompt diagnosis and treatment are therefore necessary to prevent progression of audiologic, vestibular, and facial nerve dysfunction, which may also be present. Some of these uncommon lesions are not well characterized, with a variety of confusing nomenclature and classification schemes based upon historical precedent or an incomplete knowledge base. As understanding of the underlying pathophysiology and molecular biology of these lesions advances, the ability to classify, characterize, and treat them will hopefully also improve.
Glomus Tympanicum Tumors
The most common tumor of the middle ear and second most common tumor found in the temporal bone is the paraganglioma, commonly referred to as the glomus tumor.  Chemodectoma is another term occasionally used to describe this tumor. Glomus tumors originate in the paraganglia, which exist throughout the temporal bone, including on the jugular dome, the promontory of the middle ear, and along the Jacobson and Arnold nerves. This anatomy accounts for the predilection of glomus tumors toward these anatomic sites. The term glomus was applied to these tumors when their origin was believed to be similar to true glomus (arteriovenous) complexes. Despite being a misnomer, the nomenclature has persisted.
An image depicting glomus tympanicum tumor can be seen below.
Glomus tumors involving the temporal bone are classified according to their anatomic location and size. Fisch and Oldring classified paragangliomas based on anatomic site, location and the presence of bony erosion.  Glasscock and Jackson categorized glomus tumors as glomus tympanicum or glomus jugulare tumors and classified glomus tympanicum tumors according to the anatomic site(s) involved.  Glomus tympanicum tumors arise along the course of the Jacobson nerve and are subclassified by size (see below). Glomus jugulare tumors arise from the dome of the jugular bulb and involve the jugular foramen and related structures. Both types are marked by slow, progressive growth, spreading via the pathways of least resistance (eg, temporal bone air cell tracts, neural foramina, vascular channels, bony haversian systems, and the eustachian tube).
Although most glomus tumors appear to arise sporadically, familial disease has been reported with an unusual genomic imprinting mode of inheritance. In this manner of transmission, tumors only occur in the offspring of an affected female when the gene is transmitted through a carrier male. This accounts for the observed tumor occurrence in skipped generations. A clear predilection for these tumors is found in females, and patients usually present after the fifth decade of life. 
Glomus tumors are typically reddish purple, vascular lobulated masses. Histologically, they resemble normal paraganglia with characteristic clusters of chief cells, termed zellballen (the literal German translation is "cell balls") in a highly vascular stroma. This pattern is enhanced on silver staining, which is useful diagnostically. Sustentacular cells and nerve axons, seen in normal paraganglia, rarely appear in paragangliomas.
Because of the vascularity of these tumors, pulsatile tinnitus is often the first presenting symptom. Further growth causes conductive hearing loss as ossicular mobility is impaired. Hearing loss is present in approximately half of patients. Continued expansion may cause the tumor to erode laterally through the eardrum, mimicking a friable bleeding polyp, or it may expand medially, causing facial nerve dysfunction, sensorineural hearing loss, or vertigo. As with other paragangliomas, glomus tympanicum tumors have the potential to secrete catecholamines. Less than 25 cases of catecholamine-secreting glomus tumors have been reported. These patients may present with headaches, diarrhea, palpitations, or hypertension, and while routine screening for urine metanephrines is not recommended, patients with symptoms suggestive of a functionally active tumor should be tested.
In a large series of 80 patients, presenting symptoms, in order of decreasing frequency, were pulsatile tinnitus (73%), hearing loss (conductive 49%, mixed 11%, sensorineural 6%), aural pressure/fullness (39%), vertigo/dizziness (16%), otalgia (16%), and bloody otorrhea (6%).
The Brown sign, which consists of a purple-red middle ear mass that blanches with positive pneumatic otoscopy, was seen in less than 10% of patients.
Differentiation between glomus tympanicum and jugulare tumors is not always possible by physical examination alone since both lesions typically involve the middle ear. Furthermore, other vascular lesions of the middle ear (eg, aberrant carotid artery or high-riding jugular bulb) may mimic a glomus tumor. Thus, radiographic evaluation prior to biopsy or surgical intervention is important.
A high-resolution temporal bone CT scan demonstrating a contrast-enhancing mass limited to the middle ear at the level of the cochlear promontory with an intact plate of bone at the lateral aspect of the jugular fossa suggests the diagnosis of glomus tympanicum. CT scanning is also useful for evaluating the degree of bony erosion and the tumor's relationship to surrounding temporal bone structures.
MRI, though not as helpful as CT scanning in evaluating bony changes within the temporal bone, is superior in identifying the extent of the tumor and defining the relationship of the tumor to surrounding structures once it has extended beyond the confines of the middle ear. Because the middle ear mass could be the tip of a larger glomus jugulare invading the middle ear from the jugular foramen, both CT scan and MRI are critical components of the diagnosis. 
The appearance of a paraganglioma on MRI reflects its highly vascular nature. Glomus tumors are isointense on T1-weighted images and brightly enhance with gadolinium. They typically possess numerous signal voids due to the vascular channels within them. On T2-weighted images, they demonstrate increased signal intensity in the solid portions of the tumor with persistent flow voids in the vascular portions. This characteristic “salt-and-pepper” pattern secondary to punctuate flow voids seen in larger paragangliomas is not appreciated in tumors smaller than 2 cm. Some advocate that the imaging study be carried down to the level of the carotid bifurcation to determine if multiple tumors exist, as multicentricity occurs in 5-10% of patients.
If the lesion is extensive, angiography may help further evaluate glomus tumors, but it should be deferred until the preoperative period, when both diagnostic and therapeutic (embolization) measures can be accomplished in a single study. Angiography allows determination of arterial supply, degree of vascularity, degree of arteriovenous shunting, evidence of major venous sinus occlusion, and confirmation of the diagnosis. It can evaluate the right, left, internal, and external carotid systems for evidence of multiple early lesions with a single study. Embolization is usually performed at the time of angiography as a preoperative maneuver to limit surgical blood loss. Because of the limited size and extent of most glomus tympanicum tumors, angiography and embolization are rarely necessary.
Magnetic resonance angiography and venography can also aid in the diagnosis of vascular lesions of the temporal bone, including glomus tumors. The role of these newer radiographic modalities in the evaluation of glomus tumors is still being defined. As previously stated, angiography, while useful for larger lesions, is not required for small glomus tympanicum tumors limited to the middle ear that can be visualized by less invasive techniques such as magnetic resonance angiography.
Surgery is the principle mode of therapy for glomus tympanicum tumors. [2, 6] Small lesions limited to the promontory that can be visualized completely by otoscopy and are confined to the mesotympanum on a CT scan can be approached via a transcanal incision and a tympanomeatal flap to expose the middle ear. Some authors have advocated the use of the diode or potassium titanyl phosphate (KTP) laser for tumor resection. Lesions extending to the hypotympanum are best exposed through a postauricular extended facial recess approach combined with an anterior tympanotomy. Extremely large lesions may require an infratemporal fossa approach, similar to a glomus jugulare. 
Using these methods, complete tumor removal can be achieved in more than 90% of patients. Closure of the air-bone gap can be expected in most patients, while approximately 10% experience some sensorineural worsening.
For poor surgical candidates, radiotherapy alone may be an option for palliation. Although radiation therapy does not eradicate the tumor, good local control and symptomatic relief may be achieved without significant morbidity.
Peripheral Nerve Sheath Tumors
Peripheral nerve sheath tumors originate from Schwann cells in the peripheral nervous system. The most common benign peripheral nerve sheath tumors are schwannomas and neurofibromas, and up to 45% of these lesions occur in the head and neck. The most common tumor of the temporal bone and cerebellopontine angle is the schwannoma, accounting for approximately 6% of all intracranial tumors and approximately 91% of tumors in and around the temporal bone.
Schwannomas usually arise within the internal auditory canal, cerebellopontine angle, or jugular foramen. However, they occasionally occur within or adjacent to the middle ear and in these cases usually arise from the facial nerve. Extension of a schwannoma from outside the middle ear may also present as a middle ear mass. Schwannomas of the facial nerve are rare, and although the exact incidence is unknown, temporal bones studies have found facial nerve schwannomas in less than 0.1% of specimens. Schwannomas arising from the facial nerve are reported to occur at a ratio of 3:1 as compared with neurofibromas. No age predilection exists, and facial nerve sheath tumors have been reported in infants.
Middle ear schwannomas may arise from the facial nerve, chorda tympani nerve, Jacobson nerve, or Arnold nerve, with the facial nerve being the most common nerve of origin. Schwannomas have been identified along the entire course of the facial nerve, although intratemporal tumors appear to be much more common than intracranial tumors. Within the temporal bone, the most common sites of involvement, in descending order, are the geniculate ganglion, labyrinthine segment, tympanic and vertical segments, and the internal auditory canal. Multiple sites of involvement are common, and tumors are not typically confined to a single segment. The tumors tend to grow longitudinally along the lumen of the fallopian canal and may prolapse into the middle ear and out of the stylomastoid foramen. Some facial nerve schwannomas display multicentricity evidenced by multiple discrete intraneural connections, sometimes described as a string of pearls.
In contrast to the more commonly appearing vestibular schwannoma (ie, acoustic neuroma), facial nerve schwannomas tend to grow at a slower rate and are often present for years before detection. Because of the facial nerve's intimate relationship with the sensory organs, otic capsule erosion is more common in facial nerve schwannomas, occurring in as many as 30% of patients.
Facial nerve dysfunction (eg, palsy, twitch) is the hallmark of clinical presentation and is evident on clinical examination in 25-50% of patients. The most common pattern is a slowly progressive palsy, often accompanied by hyperfunction manifested as limited twitch or full hemifacial spasm. Recurrent acute paralytic episodes with partial or complete recovery may also occur. Patients are commonly misdiagnosed with Bell palsy with the first episode of paralysis. Successive bouts of palsy then ensue, with increasingly poor facial nerve function. This presentation of recurrent and progressive episodes of facial palsy is a classic characteristic of facial nerve schwannoma. Patients without functional recovery from an idiopathic facial paralysis after 3 months or with a history of recurrent Bell palsy should undergo enhanced MRI to search for tumor or facial nerve pathology. Prolonged pain should also raise suspicion for a diagnosis other than idiopathic facial palsy.
Patients may also present with normal facial nerve function, as the facial nerve is surprisingly resistant to compression. An estimated 50% of facial nerve fibers must degenerate before clinical signs of palsy are detected. In one study of 48 patients with facial nerve neuromas, 26 presented with normal facial function. Additional presenting symptoms that have been described include conductive or sensorineural hearing loss, tinnitus, vertigo, and otorrhea. A surgeon performing an exploratory tympanotomy for conductive hearing loss may occasionally encounter a small facial nerve schwannoma impinging upon the stapes bone and oval window. This condition leads to a hearing loss similar to that observed in otosclerosis. Ear examination may demonstrate a mass behind the eardrum in as many as 29% of patients.
Facial nerve schwannomas are often found incidentally during routine middle ear or mastoid surgery. Since biopsy of a facial nerve schwannoma in the middle ear usually results in facial paralysis, appropriate imaging studies are recommended prior to obtaining a biopsy of any middle ear tumor.
In cases of a facial nerve schwannoma, high-resolution temporal bone CT scan typically reveals enlargement of the fallopian canal along its length. Ossicular erosion and involvement of the horizontal semicircular canal may also be seen; however, these findings are nonspecific and may be present in other middle ear pathologic conditions such as paraganglioma and cholesteatoma. One study of 4 patients with facial nerve schwannoma concluded that a soft tissue mass in the middle ear bounded anteriorly by a thin rim of bone (“bony crescent sign”) may be a specific indicator of a facial nerve schwannoma.
The characteristic MRI appearance of schwannomas is isointense or hypointense on T1-weighted images, hyperintense on T2-weighted images, and marked enhancement with gadolinium. An enhancing enlargement of varying thickness along a large segment of facial nerve is considered highly suggestive of schwannoma. Although high-resolution CT scanning can reveal these tumors because of their osseous erosion, MRI is a more sensitive diagnostic tool. However, both modalities are useful for surgical planning.
Site-of-lesion tests (eg, Schirmer test of lacrimation, stapedial reflex testing), while theoretically attractive, are not completely reliable and have become largely obsolete because of the availability of CT and MRI scans.
Treatment for facial nerve schwannomas involves either conservative observation, conventional microsurgery, or stereotactic radiosurgery. Simple observation with serial MRI scanning is warranted for tumors that are identified incidentally and are small and nonsymptomatic. However, for tumors that are larger, symptomatic, and growing, causing facial nerve weakness, treatment is indicated.
Although a conservative approach is warranted at times for lesions limited to the transverse or descending portions of the nerve, excision is often indicated, as growth of the lesion may lead to erosion of surrounding structures. A tympanomastoid approach may be used, but lesions that involve the labyrinthine segment of the facial nerve, internal auditory canal, or geniculate ganglion require the addition of an extradural middle cranial fossa approach. If cochlear function has been destroyed, then a translabyrinthine approach may be used. 
Occasionally, removing a facial nerve schwannoma with preservation of the nerve itself is possible;  more commonly, nerve repair with an interposition graft is necessary. This is typically accomplished with a greater auricular or sural nerve graft. In general, patients with long-standing facial nerve paralysis tend to have poorer postoperative facial nerve function.
The decision of when to remove a facial nerve neuroma depends upon a number of factors. The advantages of removing the tumor early, while it is small, include assurance that the tumor is completely resected with the least likelihood of injuring adjacent structures, including the hearing and balance organs. Additionally, a maximum number of surviving healthy neurons for grafting the nerve are available.
However, the principle disadvantage of removing the tumor early is that the patient often has good nerve function in this situation, and tumor removal nearly always destroys residual nerve function. Further, grafting a transected nerve rarely results in facial function better than a grade III/VI (House-Brackmann Grading Scale). Thus, many surgeons take a middle-of-the-road approach by delaying surgery until facial nerve function has deteriorated beyond a grade III/VI. However, surgery should be instituted sooner if adjacent structures are in jeopardy (ie, CNS or inner ear organs), any question exists regarding the diagnosis, or the tumor is growing rapidly.
Stereotactic radiosurgery has been advocated as a treatment for facial nerve schwannomas, the primary goal of this treatment being to maintain the existing level of facial nerve function in the patient by preventing further growth of the neoplasm. However, long-term data is as yet insufficient to adequately evaluate this treatment modality in comparison with conventional surgery. [10, 11]
A study by Li et al indicated that in patients with neurofibromatosis type 2, vestibular schwannoma response to antiangiogenic therapy can be predicted by dynamic contrast-enhanced MRI findings, including the baseline tumor volume, relaxation rate, and contrast transfer coefficient. 
Middle Ear Adenoma
Middle ear adenomas (MEA), also recognized as neuroendocrine adenomas, are benign neoplasms first described in 1976. Previous nomenclature applied to this class of tumors includes ceruminoma, ceruminous adenoma, and monomorphic adenoma. Carcinoid tumors of the middle ear were previously thought to be a distinct entity, but are now recognized as a subtype of middle ear adenomas. No single classification scheme has yet been established. 
MEAs are thought to arise from pluripotent cells in the middle ear mucosa and may have mixed patterns of differentiation, ranging from purely epithelial (adenoma) to purely neuroendocrine (carcinoid). They are nonencapsulated and demonstrate solid, glandular, or trabecular architecture.
Various immunohistochemical markers have been reported to be present in middle ear adenomas.  Most tumors are positive for human pancreatic polypeptide, cytokeratin, and chromogranin. Other common markers include synaptophysin, CAM 5.2, CK7, vimentin, and neuron specific enolase. Not all markers may be positive in a given tumor, and no single marker is considered pathognomonic for MEA. Cells do not demonstrate papillary features, which would suggest a papillary adenocarcinoma (also known as endolymphatic sac tumor). Middle ear carcinoid tumors, also described as middle ear adenoma with neuroendocrine differentiation, exhibit similar immunohistochemical features and tumor architecture as other types of middle ear adenomas and are thus included within this class of tumors.
Presenting symptoms of middle ear adenomas, as with most middle ear neoplasms, are nonspecific and include hearing loss, tinnitus, vertigo, and ear fullness. Patients often have conductive hearing loss due to entrapment or erosion of the ossicles. Rare cases of facial weakness have been reported, thought to be caused by compression of the facial nerve. Only one case of carcinoid syndrome associated with palpitation, dizziness, and flush attacks similar to that seen in carcinoid tumors of the gastrointestinal tract has been reported. No gender predominance for middle ear adenomas exists, and the mean age at presentation is generally the fifth decade of life, although a middle ear adenoma occurring in a 13-year-old has been reported. Examination of the ear often reveals an intact eardrum with a soft tissue mass in the middle ear.
Diagnosis and treatment
High-resolution CT scans add to the clinical examination and usually demonstrate a soft tissue mass confined to the middle ear without associated bone destruction. MRI characteristics include low-to-intermediate intensity on T1-weighted images, high intensity on T2-weighted images, and enhancement with gadolinium. Because these lesions are commonly confused with chronic otitis media, the diagnosis is rarely made preoperatively; it is typically made during a routine mastoidectomy. Surgical excision is the only curative treatment for these lesions. If the ossicular chain is enveloped by the tumor it should be removed, as recurrence in up to 18% of patients may occur if the ossicles are left intact.
Choristoma is the pathological term given to a cohesive mass of histologically normal tissue occurring in an inappropriate anatomic location. While most reports address salivary gland choristomas, neural and sebaceous choristomas have also been described. Choristomas are extremely rare in the temporal bone; less than 30 cases of middle ear choristomas have been reported in the English-language literature.
One theory on the development of middle ear choristoma is that salivary gland tissue becomes trapped during the embryonic fusion of the tympanic, mastoid, and squamous portions of the temporal bone, leading to the formation of salivary choristomas. Neural rests of tissue are believed to gain access to the middle ear via Hyrtl’s (tympanomeningeal) fissures during development, giving rise to the less common neural choristoma.
Microscopically, choristomas of the middle ear are characterized by well-formed serous and mucous acini arranged randomly or in a lobular formation. Mucinous microcysts and fibroadipose tissue components have also been described. Macroscopically, the tumors are lobulated and firm. Occasionally the tumor is attached to the middle ear by a fine stalk.
Choristomas typically arise in the posterosuperior tympanum, although they vary in size and may fill the entire tympanic cavity. They are frequently associated with ossicular anomalies, particularly an absent or malformed incus or stapes. Facial nerve dehiscence or displacement is also common. Because of this frequent association, a second branchial arch embryologic etiology has been proposed.
Clinical presentation and treatment
Choristomas have been reported in individuals aged 11 months to 52 years, and no sex predilection is described. They are typically unilateral, although bilateral involvement has been reported. These benign tumors grow slowly and tend to produce few symptoms other than a conductive hearing loss in the affected ear correlating with the degree of ossicular involvement. Other reports describe serous otitis media, tinnitus and otorrhea as presenting symptoms.
Treatment is determined by the size and location of the tumor. Small tumors or those attached solely by a thin stalk may be readily excised. However, larger or broad-based tumors must be approached with a degree of caution. Because of the frequent association of choristomas with the facial nerve, temporary or permanent palsy has been reported in 25% of patients after tumor resection. Ossiculoplasty has been successful in correcting conductive hearing loss in approximately two thirds of patients. Because little to no tumor growth over time is usually observed, and no evidence of malignant degeneration is reported with middle ear choristomas, conservative management with serial examinations is acceptable for those wishing to forego surgery.
Hemangiomas and Vascular Malformations
Historically, the literature on benign vascular tumors has lacked consistent nomenclature, contributing to widespread misunderstanding of these lesions. The term hemangioma has often been used to describe any vascular lesion and is commonly preceded by descriptive but confusing and nonspecific terms, such as strawberry, cavernous, and capillary. In 1982, a new system of classification of vascular tumors was developed based upon the clinical behavior and growth characteristics of these lesions. The classification groups vascular tumors into two categories, hemangiomas and vascular malformations.
Hemangiomas usually manifest during the first month of life and are characterized by a rapid growth period (proliferative phase) followed by a slow period of involution. Hemangiomas are categorized further on the basis of depth within the dermis into cutaneous (ie, entirely within papillary dermis), subcutaneous (ie, into the reticular dermis or subcutaneous fat), or compound, which contains elements of both. Less than 15 cases of isolated middle ear hemangiomas have been reported in the literature. There has been one report of an endothelial hemangioendothelioma occurring in the middle ear; these rare lesions exhibit biologic potential that is intermediate between hemangiomas and angiosarcomas.
Vascular malformations are always present at birth and grow in proportion to body growth without regression. They can be arterial, capillary, venous, lymphatic, or any combination. Some have further divided these vascular malformations into low-flow lesions (venous malformations) and high-flow lesions (arteriovenous malformations). Vascular malformations of the temporal bone are also exceedingly rare entities, comprising fewer than 1% of all temporal bone tumors.
Unfortunately, even recent otologic literature does not differentiate between these two types of lesions, which makes clinical comparisons difficult. To add a further element of confusion, some have reported that vascular lesions of the temporal bone frequently contain elements of both hemangiomas and vascular malformations. However, most vascular lesions of the temporal bones are probably subcategories of vascular malformations.
Histologically, hemangiomas are characterized by endothelial hyperplasia and an increase in the number of mast cells during the proliferative phase, followed by fibrosis, fatty infiltration, decreased cellularity, and normalization of the mast cell count during involution of the lesion.
In contrast, vascular malformations are collections of abnormal vessels with normal endothelium and mast cell counts. Using these histologic criteria, lesions commonly identified by the term cavernous hemangioma are more appropriately classified as vascular malformations. Alternatively, the term capillary hemangioma describes a true hemangioma, but as some authors have indicated, these have not been reported in the temporal bone. The overwhelming majority of vascular malformations manifest within the internal auditory canal or at the geniculate ganglion. In rare cases, they may arise within the middle ear. The extensive blood supply surrounding Scarpa’s ganglion and the geniculate ganglion make this region relatively hospitable to tumors. Most tumors are smaller than 1 cm at the time of presentation.
Patients typically present between the third and seventh decades of life. When the geniculate ganglion is the site of origin, a cranial nerve VII dysfunction (e.g., weakness, twitch, or both) is nearly always present. Overall, facial nerve dysfunction is present in approximately 80% of temporal bone vascular malformations and is usually the reason patients seek medical attention. Other symptoms noted on clinical presentation include tinnitus, conductive hearing loss (more common with geniculate ganglion malformations), progressive sensorineural hearing loss (more common with internal auditory canal tumors) and vertigo.
Diagnosis and treatment
High-resolution CT scanning and MRI reveal the lesion and provide complementary information. MRI demonstrates all tumors within the internal auditory canal and some tumors near the geniculate ganglion. The lesions appear hyperintense on T2-weighted images and tend to be more hyperintense than vestibular schwannomas. Some geniculate ganglion lesions are difficult to visualize on MRI, but calcium deposits within the tumor can be detected on a high-resolution CT scan.
Venous malformations of the geniculate region may be differentiated from other temporal bone tumors based upon radiographic appearances. A focal, enhancing lesion of the geniculate ganglion that is sessile upon the middle fossa floor, erodes bone diffusely, has irregular margins, and contains flecks of calcification is most likely a meningioma. In contrast, facial nerve schwannomas typically cause smoothly marginated expansion and tend to be less focal, extending along the fallopian canal longitudinally.
The treatment of choice is surgical excision with removal of normal bony margins by drill. The choice of surgical approach depends on tumor location and size, but middle fossa, transmastoid, and translabyrinthine approaches are commonly used.
Because of the destructive nature of these benign tumors, intratemporal facial nerve grafting is frequently required. Facial nerve repairs are required more often for geniculate vascular malformations than for those originating within the internal auditory canal. When facial paralysis is of recent origin or when partial function remains, the native facial nerve can often be preserved. However, in long-standing complete palsies, a graft is almost always required.
Surgery is generally successful at eradicating lesions, with a low likelihood of recurrence after complete excision. Results of facial nerve function following repair are good (i.e., House-Brackmann grade II-IV) except when nerve repair is delayed more than 1 year from the onset of the palsy. Approximately two thirds of patients undergoing middle fossa or transmastoid procedures can expect postoperative hearing preservation to within 10 dB of preoperative speech thresholds. 
Langerhans Cell Histiocytosis (Eosinophilic Granuloma)
Langerhans cell histiocytosis, previously referred to as histiocytosis X and reticuloendotheliosis, is a rare disorder characterized by the accumulation of Langerhans cells that may occur in solitary or multiple forms. The diffuse disease spectrum comprises 3 clinical entities. Eosinophilic granuloma is the mildest form and consists of multifocal bony erosions limited to the skull, long bones, ribs, vertebrae, pelvis, maxilla, and mandible. Hand-Schüller-Christian syndrome and Letterer-Siwe syndrome are the more chronic and severe forms of Langerhans cell histiocytosis, respectively, and are marked by multi-organ involvement.
The underlying pathology in all 3 forms of Langerhans cell histiocytosis is the proliferation of Langerhans cells, which are histiocytes involved in cell-mediated immunity, osteoclastic activity, and eosinophilic infiltration. The cause of the abnormal proliferation is unknown, as is whether the Langerhans cells are normal or pathologic. Proposed theories of the genesis of the disease include metabolic, genetic, infectious, neoplastic, and immunologic causes. 
Eosinophilic granuloma consists of a soft, friable, red mass containing histiocytes, eosinophils, lymphocytes, plasma cells, and multinucleated giant cells. The presence of histiocytes, with characteristic Birbeck granules (i.e., trilaminar rod-shaped organelles within the nuclear cytoplasm) seen under electron microscopy, is considered diagnostic.
Solitary eosinophilic granuloma most commonly appears in children older than 5 years and in young adults, in contrast to the more severe systemic forms of Langerhans cell histiocytosis, which tend to occur in infants and young children. Temporal bone lesions have been described within the lateral mastoid and petrous apex, and they may also involve the entire temporal bone. Prevalence of otologic involvement in Langerhans cell histiocytosis has been estimated from 15-61% of patients and may be the sole presenting symptom in 5-25% of children.
The lesions typically manifest as a painful postauricular soft tissue swelling. Otorrhea, granulation tissue within the external auditory canal, and otitis externa are also common at presentation. Conductive hearing loss by either soft tissue obstruction or, less commonly, ossicular erosion may also be present. Sensorineural hearing loss from destruction of the bony labyrinth has also been described. Facial palsy may be associated with the more severe forms of Langerhans cell histiocytosis in approximately 3% of patients.
Diagnosis and treatment
Skull and plain radiographs demonstrate destructive osteolytic lesions of the temporal bone that are commonly mistaken for symptoms of suppurative mastoiditis, cholesteatoma, or a metastatic osteolytic lesion. High-resolution CT scanning reveals a destructive lesion and is helpful in demarcating the areas of temporal bone involvement. On an MRI study, the lesion is usually hypointense on T1- and T2-weighted images and enhances with gadolinium.
Once the diagnosis is made, treatment consists of conservative curettage followed by low-dose radiotherapy. Intralesional steroid injections have also been successful in some reported cases. When multisystem involvement is present, chemotherapy and intravenous steroids are advocated. Patients may be at risk for developing secondary acquired cholesteatoma in the setting of Langerhans cell histiocytosis and should be managed surgically to rule out recurrent disease.
When the disease is limited to the temporal bone, eosinophilic granuloma typically resolves after local excision or radiation without recurrence. Surgery usually consists of curetting the bony cavity created by the tumor. However, the disease may progress to a more disseminated form, and close follow-up observation is warranted. With multisystem non-osseous involvement, the prognosis is much poorer, with the mortality rate reported at approximately 40%.
Other Tumors of the Middle Ear
Primary extracranial meningiomas are rare neoplasms that occur in fourth and fifth decades of life. Although they most often affect the skin, they may occur in the middle ear, external auditory canal, or temporal bone. Histologic findings are similar to intracranial meningiomas, and the primary treatment modality is surgical excision. An endolymphatic sac tumor confined to the middle ear without apparent connection to the endolymphatic sac, as well as a lymphatic malformation isolated to the middle ear, have been reported.