Malignancies of the Temporal Bone: Limited and Radical Temporal Bone Resection

Introduction

Although carcinoma of the temporal bone is uncommon and aggressive, the best outcome depends on careful evaluation and planning that result in a complete resection with pathologically clear surgical margins. The most common lesion is primary squamous cell carcinoma of the external auditory canal (EAC). Tumors involve the temporal bone through primary growth, direct extension from surrounding structures, and metastatic spread. The consequences of these lesions include morbidity owing to anatomical remodeling, intracranial extension, perineural spread, vascular encasement and dural invasion, and ultimately death.

Historically, carcinoma of the temporal bone was an ominous diagnosis, but advancements in diagnostic and surgical techniques have led to greatly improved outcomes. The successful resection of T1 disease has survival outcomes of 95%, and the treatment of T2 and T3 disease has survivals of 85% when a clear surgical margin is combined with postoperative radiation therapy. ^,

A multidisciplinary approach to the diagnosis and treatment of these lesions offers the best possible outcome. Surgery and postoperative radiation represent the principal treatments; however, the role of chemotherapy continues to be explored. ^, The type of resection needed is determined by the extent of disease. A sound oncological resection characterized by clear pathological margins can be achieved through a partial temporal bone resection (PTB), subtotal temporal bone resection (STB), or total temporal bone resection (TTB) with additional simultaneous procedures as parotidectomy, facial nerve resection, mandibulectomy, and cervical lymphadenectomy as indicated. In addition to planning the oncological surgical resection, treatment planning must include consideration of the reconstructive options to minimize postoperative complications.

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 in the United States. Squamous cell carcinoma accounts for 86% of these tumors. The possible etiological factors include industrial exposure to petroleum-based products, topical disinfectants, topical manipulation, and chronic infection. Basal cell carcinoma, adenoid cystic carcinoma, adenocarcinoma, and ceruminous carcinoma occur less frequently. Malignant tumors of mesenchymal origin are as rare, with rhabdomyosarcoma occurring most frequently. 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; however, both are rare.

Salivary gland tumors are more likely to involve the temporal bone through direct extension from the parotid gland. The anatomical relationship between the temporal bone and the 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. 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. In addition, benign masses have a tendency to compress or remodel adjacent tissue, rather than invade it. This tendency allows for the 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 more readily involves the adjacent tissue. 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 the direct invasion of the skull or involvement of the lower cranial nerves at the jugular foramen. Direct extension into the 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 et al. found that adenocarcinoma occurred most commonly, followed by adenoid cystic carcinoma and mucoepidermoid carcinoma. In a recent update with 15 patients, carcinoma ex-pleomorphic and parotid squamous cell carcinoma were the most common.

Malignancies involving the temporal bone present a formidable problem. Without treatment, these lesions result in high 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 nononcological intervention frequently resulted in the spread of the lesion to the 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 the 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 hearing 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 can be used to determine resectability and the need for revascularization. Consideration should also be given to embolization when prominent vascularity of the lesion makes intraoperative hemorrhage a concern. When the workup is complete, proper tumor-node-metastasis (TNM) staging can occur, which provides a basis for discussing treatment options and prognosis with the patient.

The close proximity of the vital structures within and adjacent to the temporal bone requires an accurate assessment of the involved anatomy. Together, CT and MRI are helpful in establishing the tumor extent, the involvement of critical structures, and the best surgical plan.

High-resolution CT is essential to preoperative staging. Arriaga et al. reported 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.

MRI should be used to examine tumors relative to the dura, brain, cerebrospinal fluid, and skeletal muscle. MRI also offers the advantage of imaging in multiple planes. T1 images help to determine spatial relationships and bone marrow involvement, whereas T2 images 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 establishes 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 with treatment, the patient should be informed in advance. Ossicular chain reconstruction or a bone-anchored cochlear stimulator may be indicated when hearing is absent or sacrificed in the involved ear.

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 is performed with close monitoring. Neurologic change during balloon occlusion is likely the most reliable finding to determine when carotid sacrifice may be tolerated. The examination may be complemented by Doppler ultrasonography of the ipsilateral middle cerebellar artery, single-proton emission computed tomography, PET, xenon-enhanced CT, or functional MRI, particularly in patients who may not have reliable neurologic examinations. If there is concern about the toleration of carotid sacrifice, the management may include carotid bypass with prophylactic or intraoperative saphenous grafting, preoperative carotid stenting, or nonsurgical management. The venous side of imaging must not be ignored. If the torcular Herophili is not patent, then the drainage from the ipsilateral to the opposite sigmoid-transverse-jugular system is obstructed and venous infarction may occur.