Temporal Bone Cancer by Paul W. Gidley & Franco DeMonte

Author:Paul W. Gidley & Franco DeMonte
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Diagnostic Studies

Cross-sectional imaging is necessary both to characterize a lesion and to determine its extent. Temporal bone lesions can spread locally and intracranially, to deep neck spaces, subcutaneous tissue, or the temporomandibular joint. Depending on the location, an assessment of regional lymphadenopathy and distant metastasis is prudent for treatment and prognosis. Plain X-rays may show signs of temporal bone lesions, e.g., punched out skull lesions in LCH but are not as important for treatment planning. One should not underestimate the importance of plain films and ultrasound in the diagnosis of lesions and neck metastasis, but they will not be discussed in this chapter.

Computer tomography (CT) and magnetic resonance imaging (MRI) are often complementary in the diagnosis and management of temporal bone lesions. The complementary role is highlighted by the relative strengths and weaknesses of each modality.

Temporal bone lesions often destroy the integrity of the temporal bone. CT scanning has the advantage of delineating the bony structures within the temporal bone. With a CT scan, the ossicles, skull base, bony labyrinth, vestibule, internal auditory canal, mastoid air cells, fallopian/facial nerve canal, Eustachian tube, and petrous apex can be evaluated. There is often a clear difference between a lesion, such as a dermoid cyst which has a pushing border, versus destructive lesions, such as LCH or rhabdomyosarcoma. CT helps to narrow the differential diagnosis, but one can only deduce so much from the interaction of the lesion with the surrounding bony structures. When the lesion spreads outside the limits of the temporal bone, it can be difficult to delineate the true limit of the lesion as it enters the soft tissue or the brain. Intracranial spread or perineural invasion may not be readily recognized. Even with these limitations , CT is a valuable tool in assessing cervical lymphadenopathy. In children, temporal bone CT exposes the child to radiation; the long-term risks, of which, are not completely understood.

Magnetic resonance imaging (MRI) has the disadvantage that it does not display bony destruction/replacement as well as CT scan. However, the resolution of CT cannot be compared to the resolution on MRI for lesions that are infiltrating the brain, parotid space, masticator space, parapharyngeal space, infratemporal fossa, and subcutaneous tissue. The multiple imaging sequences of MRI refine the differential diagnosis, including T1-, T2-, and diffusion-weighted (DWI) and echo planar, just to name a few. Gadolinium contrast can help to differentiate the wide array of pathologies that can affect the temporal bone. Young children usually need to be sedated for an MRI, and the effect of sedation and anesthesia on the neurocognitive development of children is an area of concern that demands further research. MRI does come with an increased cost. Table 14.1 shows CT and MRI characteristics of common pediatric temporal bone malignancies.Table 14.1 Differential diagnosis of temporal bone masses and imaging characteristics on CT and MRI

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