TUMOR CONSIDERATIONS

The incidence of tumors of the temporal bone is 200 new cases per year with a frequency of 6 cases per 1 million. Squamous cell carcinoma accounts for 86% of these tumors. Possible etiologic factors include industrial exposure to petroleum-based products, topical disinfectants, and chronic infection. Basal cell carcinoma, adenoid cystic carcinoma, adenocarcinoma, and ceruminous carcinoma occur less frequently.^3–5 Tumors of mesenchymal origin are as rare, with rhabdomyosarcoma occurring most frequently.⁶ Salivary gland tumors can originate from ectopic rests of salivary tissue within the middle ear (pleomorphic adenoma has been described in that location), or from minor salivary glands within the EAC, but both are rare.⁷

Salivary gland tumors are more likely to involve the temporal bone through direct extension from the parotid gland. The anatomic relationship between the temporal bone and parotid gland is responsible for this tendency. The parotid gland is located in close proximity to the mastoid and tympanic portions of the temporal bone. It communicates directly with the cartilaginous EAC through the fissures of Santorini and foramen of Huschke.⁸ The stylomastoid foramen, carotid canal, jugular foramen, petrotympanic fissure, and eustachian tube provide avenues for intratemporal extension. In primary temporal bone carcinoma, these anatomic pathways are particularly significant as routes for extension beyond the temporal bone to the adjacent parotid tissue and soft tissue at the base of the skull base.

In rare cases of temporal bone involvement by benign tumors of the parotid gland, symptoms of a facial mass, trismus, or compression of the parapharyngeal space by tumor usually precede temporal bone involvement.⁹ Additionally, benign masses have a tendency to compress or remodel adjacent tissue, rather than invade it. This tendency allows for extirpation of a benign parotid neoplasm, in some cases, without requiring a formal temporal bone resection. These lesions can be removed through traditional parotidectomy techniques. Disarticulation of the mandibular condyle, resection of the EAC, or mastoidectomy may be necessary to assist with resection. Pleomorphic adenoma of the tail of the parotid gland can manifest as a subcutaneous mass of the floor of the lateral portion of the EAC. This situation is best managed with combined superficial parotidectomy with mastoidectomy and postauricular canalplasty.

Temporal bone involvement by malignancies of salivary gland origin is aggressive and involves adjacent tissue more readily. Tumors can develop insidiously and relatively asymptomatically, with 75% manifesting with a painless mass and only 6% to 13% manifesting with facial nerve palsy. Symptoms may not be present until after temporal bone invasion has occurred. Pain, dysphagia, and dysphonia can occur after direct invasion of the skull or involvement of the lower cranial nerves at the jugular foramen. Direct extension into bone, fissures, and foramina are potential routes of spread. Mass lesions of the poststyloid parapharyngeal space can traverse the carotid canal and jugular foramen, and neurotrophic tumors, such as adenoid cystic carcinoma, follow the facial nerve as an avenue toward the stylomastoid foramen. Carcinoma of the auricle, anterior scalp, or face that has spread to the intraparotid lymphatics can involve the temporal bone in a similar fashion. In a review of 27 cases of advanced and recurrent parotid neoplasms requiring temporal bone resection, Leonetti and colleagues⁹ found that adenocarcinoma occurred most commonly followed by adenoid cystic carcinoma and mucoepidermoid carcinoma.

Malignancies involving the temporal bone present a formidable problem. Without treatment, these lesions result in a high incidence of morbidity and almost certain death. Extension into the otic capsule and petrous bone can result in hearing loss, vestibulopathy, cranial neuropathies, and hemorrhage. Malignant spread into the middle and posterior fossa and extension into the petroclival region or cavernous sinus portend a grim prognosis even with aggressive surgical efforts. In cases of distant metastatic disease, a temporal bone resection may still be indicated for palliation.

HISTORY AND PHYSICAL EXAMINATION

A high index of suspicion by the examiner is necessary for prompt diagnosis and treatment in temporal bone carcinoma. Symptoms of fullness, pain, or trismus without clear explanation or rapid resolution are suspicious for carcinoma. Refractory pain is a hallmark of temporal bone carcinoma. An unexplained mass of the pinna, ear canal, or middle ear should prompt closer evaluation. An insidious symptom of carcinoma that frequently causes a delayed diagnosis is persistent ear drainage. Before the advent of computed tomography (CT), most temporal bone carcinomas were diagnosed after mastoidectomy for presumed chronic otitis media. Such nononcologic intervention frequently resulted in spread of the lesion to adjacent soft tissue structures.

BIOPSY

The only way to diagnose temporal bone carcinoma definitively is by biopsy. Although it is possible to obtain a biopsy specimen of an exuberant lesion of the EAC in the office, we recommend imaging before performing any deep tissue biopsies or removing any soft tissue lesions of the middle ear to prevent inadvertent damage to the carotid, jugular bulb, or facial nerve. False-negative biopsy specimens are an important consideration in temporal bone carcinoma. These lesions are often secondarily infected, and superficial biopsy specimens may reveal only chronic inflammatory changes. If initial biopsy results are negative, we recommend performing deeper tissue biopsies in an operating room to ensure that an adequate sample has been obtained.

DIAGNOSTIC TESTS

Imaging studies and audiometric testing are crucial. Magnetic resonance imaging (MRI) and CT provide accurate information helpful in the staging of disease and determining the extent of resection needed. A preoperative hearing assessment establishes a functional baseline, the need for postoperative middle ear reconstruction when appropriate, and the potential for postoperative deficits. Angiography should be performed in all cases in which the carotid artery is at risk. When carotid resection is anticipated, cerebral blood flow analysis should be used to determine resectability and the need for revascularization. Consideration should also be given to embolization when intraoperative hemorrhage is a concern. When the work-up is complete, proper TNM staging can occur, which provides a basis for discussing treatment options and prognosis with the patient.

The close proximity of vital structures within and adjacent to the temporal bone requires an accurate assessment of the involved anatomy. CT and MRI are indispensable in this regard. The ability of CT to detail bony structures and the superb soft tissue contrast offered by MRI play complementary roles during the work-up. Together, CT and MRI are helpful in establishing tumor extent, the involvement of critical structures, and the best surgical plan.¹⁰

The use of high-resolution CT with fine cuts is recommended. Images with a thickness of 0.625 to 1.25 mm produce the best assessment of the skull base. Direct axial and coronal scans should be obtained. When advanced scanning technologies are available, reconstructed images provide resolution that is equivalent to the original data set. CT is essential to preoperative staging. Arriaga and colleagues¹¹ showed that CT can “achieve 98% accuracy in predicting pathologic involvement in temporal bone resection specimens.” CT scans have limitations, however. Distinguishing mucosal inflammation from tumor and the extension of tumor without bony erosion remains difficult. In previously operated areas, positron emission tomography (PET) combined with CT has proven useful for distinguishing scar from neoplasm in identifying tumor recurrence and guiding treatment.¹²

MRI should be used to examine tumor relative to dura, brain, cerebrospinal fluid, and skeletal muscle. MRI also offers the advantage of imaging in multiple planes. Multiplanar imaging is useful when evaluating lesions that traverse the skull base through direct extent or perineural spread. T1 and T2 fat-saturated sequences should be obtained. T1 images help to determine spatial relationships and bone marrow involvement, whereas T2 images with fat saturation help to delineate tumors that enhance brightly. Postgadolinium T1-weighted images with fat saturation should also be obtained to determine the presence and extent of perineural involvement. This involvement can manifest as foraminal widening or enhancement, replacement of fat density, or increased signal intensity.

Audiologic testing shows the functional status of the middle and inner ear. This information is useful during surgical planning and preoperative patient counseling. Conductive losses may be attributable to the presence of a malignancy in the external or middle ear. Anacusis, tinnitus, and vertigo suggest inner ear involvement. If a reduction or elimination of hearing is anticipated, the patient should be informed in advance. Ossicular chain reconstruction or a bone-anchored hearing aid may be indicated when conductive hearing is sacrificed, but sensorineural hearing is spared.

A four-vessel angiogram with venous runoff should be used in cases of carotid encasement, or when disease mandates dissection of the petrous carotid. Arterial stenosis and contour irregularity at the site of the lesion suggest malignant involvement. Close inspection of the carotid canal on CT and CT angiography is useful for carotid assessment. Temporary balloon occlusion coupled with a cerebral blood flow quantification study helps to determine when carotid sacrifice would be tolerated. Quantification studies include PET, functional MRI, and xenon-CT. Xenon-CT is the best-studied modality.¹³ An occlusional cerebral blood flow less than 30 mL/100 g/min requires carotid bypass with prophylactic or intraoperative saphenous grafting or consideration of preoperative carotid stenting.¹⁴ Cerebral blood flow less than 30 mL/100 g/min or the development of neurologic symptoms during the test indicates a high risk of perioperative stroke. These findings either preclude the surgical option or require that prophylactic revascularization be done if surgery is performed. The venous side of imaging must not be ignored. If the torcular Herophili is not patent, permitting venous drainage from the ipsilateral sigmoid-transverse system to the opposite sigmoid-transverse-jugular system, venous infarction may occur. Specific attention should be focused on the adequacy of contralateral venous drainage.

STAGING

The American Joint Committee on Cancer states that a staging system should provide a sound basis for therapeutic planning for cancer patients by describing the survival and resultant treatment of different groups in comparable form. A lack of uniformity regarding preoperative staging and treatment plans made the study of temporal bone cancer difficult. This situation has changed with the demonstration that CT accurately predicts the degree of neoplastic involvement. The supplementation of these observations with clinical findings enabled the formation of a reliable system for staging carcinoma of the EAC.¹¹ Attempts to modify this system have been made. Moody and coworkers¹⁵ proposed upstaging patients with preoperative facial nerve paralysis or paresis to T4 status when the primary tumor originates in the EAC. They proposed that the extension of tumor through tissue separating the facial nerve and EAC and tumor involving the horizontal segment of the nerve are ominous signs.¹⁵