Radiation-induced tumors of the temporal bone.

OBJECTIVE: To discuss a rare but devastating complication following radiotherapy to the head and neck: radiation-induced malignancies of the temporal bone. STUDY DESIGN: A retrospective case review comprising five patients with radiation-induced tumors involving the temporal bone. SETTING: A tertiary referral center. PATIENTS: Patients with tumors involving the temporal bone who have satisfied the criteria for being considered radiation-associated. MAIN OUTCOME MEASURES: Initial tumor histology, radiation-induced tumor histology, latency between radiotherapy and diagnosis of the radiation-associated malignancy, amount of radiation received, therapeutic interventions, and survival statistics for each patient. RESULTS: Five cases of radiation-induced tumors of the temporal bone are presented (two osteosarcomas, two fibrosarcomas, and one squamous cell carcinoma). All five temporal bone tumors occurred in individuals that had previously received > 5,000 cGy of radiation. The initial histologic diagnoses included two astrocytomas, a glomus jugulare, a malignant meningioma, and a vestibular schwannoma. There was an average latency period of 15 years (range, 7-23 years) between completion of radiation and diagnosis of the malignancy. Four patients were treated with resection plus chemotherapy, and one decided against therapy. The prognosis was poor, with survival time of 7-14 months after the diagnosis of the radiation-induced tumor. Only one patient survived > 14 months and is currently free of disease, 3 years after diagnosis of the radiation-induced tumor. CONCLUSIONS: Although radiation-induced tumors of the temporal bone occur with a very low incidence, their prognosis is extremely poor. The remote possibility of a radiation-associated tumor should be factored in when deciding upon the most appropriate therapeutic modality for individuals with neoplasms of the CNS and head and neck. Such considerations are particularly germane when contemplating radiation therapy for a benign lesion (e.g., glomus jugulare, acoustic neuroma, or meningioma) in an individual with a long predicted lifespan.

Catecholamine-secreting paragangliomas at the skull base.

Paragangliomas (glomus tumors) comprise 15% of all neoplasms at the skull base. Despite extensive growth, these tumors usually do not secrete active biogenic substances into the circulation in sufficient quantities to produce symptoms. When they do secrete large amounts of catecholamines, they will cause symptoms that mimic a pheochromocytoma. The still confusing nomenclature of paragangliomas is reviewed, and the clinical work-up, surgical treatment, and follow-up of five patients with catecholamine-secreting paragangliomas of temporal bone (3), infratemporal fossa (1), and nasopharynx (1) are presented and discussed.

Analysis of chromosome 22 deletions in neurofibromatosis type 2-related tumors.

The neurofibromatosis type 2 (NF2) gene has been hypothesized to be a recessive tumor suppressor, with mutations at the same locus on chromosome 22 that lead to NF2 also leading to sporadic tumors of the types seen in NF2. Flanking markers for this gene have previously been defined as D22S1 centromeric and D22S28 telomeric. Identification of subregions of this interval that are consistently rearranged in the NF2-related tumors would aid in better defining the disease locus. To this end, we have compared tumor and constitutional DNAs, isolated from 39 unrelated patients with sporadic and NF2-associated acoustic neuromas, meningiomas, schwannomas, and ependymomas, at eight polymorphic loci on chromosome 22. Two of the tumors studied revealed loss-of-heterozygosity patterns, which is consistent with the presence of chromosome 22 terminal deletions. By using additional polymorphic markers, the terminal deletion breakpoint found in one of the tumors, an acoustic neuroma from an NF2 patient, was mapped within the previously defined NF2 region. The breakpoint occurred between the haplotyped markers D22S41/D22S46 and D22S56. This finding redefines the proximal flanking marker and localizes the NF2 gene between markers D22S41/D22S46 and D22S28. In addition, we identified a sporadic acoustic neuroma that reveals a loss-of-heterozygosity pattern consistent with mitotic recombination or deletion and reduplication, which are mechanisms not previously seen in studies of these tumors. This finding, while inconsistent with models of tumorigenesis that invoke single deletions and their gene-dosage effects, lends further support to the recessive tumor-suppressor model.

Epidemiology, pathogenesis, and genetics of acoustic tumors.

This article reviews the epidemiology of both unilateral and bilateral (NF-2) acoustic tumors. The growth rate of acoustic tumors is examined from a clinical, radiographic, and laboratory perspective. The anatomic, histologic, and biochemical considerations as well as the influences of sex hormones on acoustic tumor formation are reviewed. Also presented are an update on the laboratory search for the NF-2 gene on chromosome 22 and recently identified DNA markers. Predictions are made concerning the potential future applications of genetic testing for prenatal or presymptomatic diagnosis of the disease that causes bilateral acoustic tumors.

Facial nerve grafting.

The techniques of facial nerve grafting have undergone several adjustments and refinements within the last 20 years. Those techniques that have stood the test of time are discussed, and new approaches to facial nerve grafting in the temporal bone are explored.

Gadolinium-DTPA enhanced magnetic resonance imaging in acoustic neuroma diagnosis and management.

Gadolinium-DTPA (Gd-DTPA) is a paramagnetic contrast agent that increases the intensity of acoustic neuromas (AN) on T1-weighted magnetic resonance imaging (MRI) scans. Over a 9-month period we have reviewed Gd-DTPA-enhanced MRI scans on 32 consecutive cases (35 tumors) involving the internal auditory canal (IAC) and cerebellopontine angle (CPA). The majority of patients (84%) were imaged on latest generation 1.5 Tesla scanners. Every tumor studied showed marked enhancement after Gd-DTPA administration. This improved contrast permitted identification of three small tumors that were not evident on unenhanced scans. Gd-DTPA appears to be particularly useful in the evaluation of recurrent or residual AN. In three patients with known residual tumor after planned subtotal excisions, the remaining tumor could only be differentiated from surrounding scar, cerebral spinal fluid (CSF), and brain parenchyma after contrast enhancement. In one of these, a small rim of tumor capsule left on the facial nerve was evident only on Gd-DTPA-enhanced T1 images. Gd-DTPA also provides a more reliable estimate of the depth of tumor penetration in the IAC. This information is useful in selecting candidates suitable for a hearing conservation approach.