MALIGNANT TUMORS OF THE EXTERNAL AND MIDDLE EAR AND MASTOID
- Imaging is critical to medical decision making in temporal bone malignancies.
- A variety of diseases of the temporal bone and adjacent sites can mimic cancers of the temporal bone.
The most common malignancies involving the temporal bone are those that arise from the skin of the pinna and periauricular region that secondarily invade the temporal bone (Chapter 24). Primary cancers of the external auditory canal (EAC) are uncommon, and those of the middle ear are rare. These include such diverse lesions such as papillary adenocarcinoma of the middle ear and endolymphatic sac and transitional cell and carcinoid tumors of the middle ear. Some carcinomas may be associated with chronic infection. Differentiation of these by imaging from the more common squamous cell carcinoma is not possible except for the rare endolymphatic cancer that is diagnosed by its morphology (Chapter 12), anatomic location, and von Hippel-Lindau syndrome association. Temporal bone tumors may be confused with chronic inflammatory disease and as a result may be diagnosed late.
Rhabdomyosarcoma may arise in the middle ear in children (Chapter 35). Ewing sarcoma (Chapter 30), osteosarcoma (Chapter 38), and other mesenchymal-origin lesions uncommonly originate from the temporal bone.
The histiocytoses frequently involve the temporal bone, mainly in the pediatric age group (Chapter 19). Other hematopoietic and lymphoid tumors rarely present primarily in the temporal bone (Chapters 27 and 28).
Metastases (Chapter 43) to the temporal bone are very unusual, although their incidence may be underestimated because the symptoms such as hearing loss and those of chronic mastoiditis are overshadowed by more disabling symptoms of the primary tumor. Metastases are usually the result of hematogenous spread and may involve both ears. The most commonly reported primary tumors are breast, lung, renal, and prostate carcinoma.1
ANATOMIC AND DEVELOPMENTAL CONSIDERATIONS
A detailed and complete knowledge of normal temporal bone anatomy is required for evaluation of cancer in this region. Computed tomography (CT) and magnetic resonance imaging (MRI) of the parotid and periparotid region, nasopharynx, surrounding deep spaces, facial nerve, and regional lymphatics also must be understood when evaluating malignancies of the temporal bone. The most common key elements in this evaluation include the following:
- Soft tissues: Parotid gland and capsule attachments to the EAC, parapharyngeal space, upper masticator space, and temporomandibular joint (Chapter 175)
- Temporal bone: EAC, roof of the middle ear and mastoid, carotid canal and jugular fossa, and petrous apex (Chapter 104)
- Nerves/Facial nerve: Brain stem to the parotid, the auriculotemporal nerve to V3, and the trigeminal ganglion (Chapter 104)
- Vascular structures: Internal carotid artery, jugular vein and bulb, and major dural venous sinuses of the posterior fossa
- Regional lymphatics: Parotid nodes and cervical lymph node levels 1 through 5, external jugular nodes, retropharyngeal nodes, mastoid, and occipital nodes (Chapters 149 and 175)
The gross anatomy most pertinent to evaluation of malignancy is summarized here.
The pinna and cartilaginous portion of the EAC are skin covered with numerous associated hair follicles and sebaceous and ceruminous glands. In the bony EAC, the skin firmly adheres to the periosteum. The entire external ear canal is about 2 to 4 cm long, the lateral third being fibrocartilage and the remainder being bone up to the bony tympanic ring where the tympanic membrane attaches and separates the EAC and middle ear (Figs. 104.21–104.23). Both the bony and cartilage parts of the EAC may be incomplete, with gaps that are filled with fibrous tissue. The temporomandibular joint lies anteroinferior to the EAC. Part of the tissue of the joint capsule may on occasion herniate into a small anteroinferior EAC bony dehiscence. The capsule of the parotid gland attaches to the cartilage of the EAC, providing a bidirectional conduit for spread of pathology arising from either structure (Fig. 104.20).
The mastoid lies posterior to the EAC and contains the descending facial canal and its nerve as it exits the skull into the stylomastoid fat pad.
The middle ear cavity is connected to the mastoid and eustachian tube. The tympanic cavity and mastoid antrum and air cells are lined by ciliated and nonciliated columnar epithelium. This epithelium extends into the eustachian tube to the nasopharynx.
The tympanic cavity and mastoid likely do not have significant capillary lymphatics, nor does the inner ear labyrinth. Capillary lymphatics are described for the mucosa. The cartilaginous portion of the eustachian tube has capillary lymphatics that drain to predominantly parotid, retropharyngeal, and level 2 nodes.
The petrous apex is home to the carotid canal. The jugular fossa is at the boundary of the petrous and mastoid portions of the temporal bone. The transverse and sigmoid sinuses drain to the jugular bulb, and one side is often dominant in this posterior fossa venous drainage pattern.
Techniques and Relevant Aspects
Imaging is indispensable for the differential diagnosis and in planning therapy for malignancies of the temporal bone. Both CT and magnetic resonance (MR) are often necessary. CT is usually the primary study because the assessment of bony detail is critical to surgical decision making. MR is used in advanced lesions to evaluate perineural spread and dural and brain involvement as well as to separate obstructive from tumor-associated mastoid and middle ear changes. Anatomic imaging usually suffices for evaluation of adjacent major vascular structures, including the dural sinuses, the jugular vein, and the carotid. Carotid balloon occlusion testing may be done if carotid sacrifice is anticipated.
CT and MRI must be carefully supervised when evaluating malignancies of the temporal bone. Even 2- or 3-mm differences in tumor extent can markedly alter the morbidity of surgical management. The techniques and supportive rationale required for such high-quality scans may be reviewed if necessary. These are summarized in Appendixes A and B.
CT scans must be done with a slice thickness of 0.50 to 0.75 and a combination of a focused (7- to 9-cm) temporal bone field of view and wider fields of view encompassing surrounding soft tissues and the adjacent brain. These must be processed with bone and soft tissue algorithms. MR studies should be focused on the precise area of interest and done with the highest possible spatial resolution. Focused studies with small field of view coils produce the best results. Coronal and axial MRI sections are fundamental. Sagittals may be used selectively. Intravenous contrast is typically used in both studies.
Pros and Cons
Most lesions of the EAC are epithelial in origin and often are biopsied before imaging. However, any subcutaneous or submucosal lesion should be studied with CT and supplemented with MR whenever necessary prior to biopsy. Lesions that are not obviously cholesteatoma and that present medial to the tympanic ring and tympanic membrane should always be imaged first with CT before biopsy. MRI is usually done second and is focused on a particular concern that might alter medical decision making. Imaging prior to biopsy can limit hemorrhagic complications of biopsy that can occur with a paraganglioma. It can also avoid rare complications such as sampling of an aberrant carotid or encephalocele. In this way, imaging may obviate middle ear exploration in some patients.
Carcinoma of the External and Middle Ear and Mastoid
Benign neoplasms such as squamous cell papilloma and adenomas are uncommon in the EAC and rare in the middle ear. Rare malignancies such as papillary adenocarcinoma and transitional cell and carcinoid tumors of the middle ear cannot be differentiated from each other by imaging. Endolymphatic sac papillary carcinoma is discussed in conjunction with petrous bone malignancies.
Carcinomas of the EAC are almost exclusively squamous cell and basal cell skin carcinomas and are the most common primary EAC lesion (Fig. 24.21 and Chapter 24). More commonly, squamous cell carcinoma and basal cell carcinoma arise from the pinna and skin over the temporal bone to involve that structure (Figs. 122.1–122.3). Melanomas and Merkel cell carcinoma can also arise from the skin in these areas to invade the temporal bone. Ceruminous gland adenocarcinoma is a rare tumor arising from modified sweat glands of the EAC. Tumors arising from the tympanic cavity, mastoid, or eustachian tube are all rare. The specific tumor types reported include squamous cell carcinoma and benign and malignant salivary gland tumors. These tend to arise from the medial two thirds of the eustachian tube and the middle ear.
Prevalence and Epidemiology
Most cancers of this region are induced by sun exposure since they are skin cancers. Immune-compromised patients have an increased incidence of these skin cancers, and these malignancies may be more aggressive in that population. Other carcinomas may arise due to long-standing infections. Others are sporadic. This is essentially a disease of adults that has no particular prevalence based on patient gender.
EAC tumors usually present as a painless skin lesion in the canal. Further growth causes minor bleeding, pain, itching, and drainage. These symptoms and signs mimic benign inflammatory disease. There may be a conductive hearing loss when the EAC is occluded or the tympanic membrane or middle ear becomes involved.
A good deal of growth may occur beneath the skin surface. A preauricular mass or fullness may be present or herald deep spread to surrounding structures. Trismus may result from invasion of the temporomandibular joint. The external ear is often involved.
Middle ear cancer may be seen in patients with long-standing middle ear inflammation (Fig. 122.4). Pain, discharge, and facial nerve palsy are possible presenting complaints. Carcinoma rarely arises in the eustachian tube. When it does, patients will usually have pain and otitis with conductive hearing loss. Advanced lesions may have associated deficits of cranial nerves VII through XII and possibly Horner syndrome. The naso-pharynx will appear normal. Imaging with CT and MRI are essential to avoid a delay in diagnosis. Physical examination typically will reveal findings that mimic benign disease unless there are cranial nerve deficits.