Differential Diagnosis of Temporal Bone and Skull Base Lesions (12 pages)

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Differential Diagnosis of Temporal Bone and Skull Base Lesions



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Differential Diagnosis of Temporal Bone and Skull Base Lesions December 2001 TITLE Differential Diagnosis of Temporal Bone and Skull Base Lesions SOURCE Grand Rounds Presentation UTMB Dept of Otolaryngology DATE December 19 2001 RESIDENT PHYSICIAN Russell D Briggs M D FACULTY ADVISOR Arun Gadre M D SERIES EDITORS Francis B Quinn Jr MD and Matthew W Ryan MD ARCHIVIST Melinda Stoner Quinn MSICS This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology Head and Neck Surgery and was not intended for clinical use in its present form It was prepared for the purpose of stimulating group discussion in a conference setting No warranties either express or implied are made with respect to its accuracy completeness or timeliness The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion Introduction A wide spectrum of diseases involves the temporal bone and skull base Primary tumors inflammatory processes and metastatic disease are a few of the many abnormalities that can exist within the temporal bone and skull base With the advent of high resolution computed tomography HRCT and magnetic resonance imaging MRI the diagnosis of many of these abnormalities is more readily apparent By classifying these processes based on location and identifying the common imaging characteristics a relatively straightforward differential diagnosis can be formulated Lesions of the Middle Ear and Mastoid Cholesteatoma Epidermoids Cholesteatomas are soft tissues masses caused by aberrant accumulation of keratin debris within a sac of squamous epithelium These are not true neoplasms as they do not exhibit cellular growth rather they are the result of squamous epithelial migration or implantation within the middle ear mastoid or petrous apex Middle ear cholesteatomas are usually distinguished as two types acquired or congenital Congenital masses are thought to arise from embryonic rests within the middle ear Acquired cholesteatomas consist of an abnormal keratinizing squamous epithelium in the middle ear epitympanum or mastoid It has been proposed that primary disease develops behind an intact tympanic membrane as a result of chronic otitis media Secondary disease results from eustachian tube dysfunction followed by a retraction pocket in the tympanic membrane which traps epithelium followed by perforation and accumulation of keratin within the middle ear Patients typically present with purulent otorrhea and conductive hearing loss Patients with congenital cholesteatoma however may present with an intact tympanic membrane and not present with otorrhea Diagnosis is typically made during otologic 1 Differential Diagnosis of Temporal Bone and Skull Base Lesions December 2001 examination HRCT may be of value in the preoperative assessment of cholesteatomas but is not always diagnostic of disease Erosion of the scutum and expansion of the antrum within areas of air cell breakdown and soft tissue density are frequent findings on HRCT Ossicular destruction erosion of the otic capsule lateral canal and erosion of the facial canal or mastoid tegmen can also be seen Routine CT is not advocated for cholesteatoma diagnosis but may be important in complicated disease revision cases intact TM history does not correlate well with physical exam MRI plays a limited role in middle ear and mastoid cholesteatomas However on T1weighted images cholesteatomas are low intensity and on T2 weighted images cholesteatomas are typically high intensity Paragangliomas Paragangliomas of the head and neck are typically benign slow growing tumors arising from widely distributed paraganglionic tissue thought to originate from the neural crest Paraganglia in the head and neck region are closely aligned with the distribution of the parasympathetic nervous system and often have a close spatial relationship with neural or vascular structures Paraganglia have been shown to have chemoreceptor roles with modulation of respiratory and cardiovascular function Paraganglia are located in many locations in the head and neck including the middle ear jugular bulb carotid bulb ganglion nodosum of the vagus nerve larynx and base of the heart Histologically paragangliomas are similar in appearance to the normal histology of the paraganglia and includes two cell types Type I cells chief cells are APUD type cells with copious cytoplasm and large round or oval nuclei Their cytoplasm contains dense core granules that store and release catecholamines Type II sustentacular cells are elongated cells that closely resemble Schwann cells although their function is not entirely clear The two cell types are arranged into clusters with a core of chief cells surrounded by sustentacular cells embedded in a fibrous stroma These clusters make up the fundamental histologic structure termed Zellballen and may be somewhat enlarged in paragangliomas Nuclear pleomorphism and cellular hyperchromatism are common in benign paragangliomas and should not be considered evidence of malignancy In fact there are no clear histologic characteristics of malignancy in these lesions Malignancy is based on the clinical finding of metastasis not on histologic examination occurs in only 3 4 of tumors The chief cells of paragangliomas have neurosecretory granules that store catecholamines however only 1 3 of these tumors actively secrete norepinephrine Catecholamines are much more likely to be secreted by glomus jugulare tumors than glomus tympanicum tumors Approximately 5 of patients with paragangliomas eventually present with multiple tumors however with a familial form of the disease over 50 exhibit multicentricity Although described as rare paragangliomas are the most common true neoplasm of the middle ear and are the most common pathologic entity affecting the jugular foramen They are second only to schwannomas as the most common neoplasm affecting the temporal bone Glomus tympanicum tumors usually originate on the promontory of the cochlea from paraganglionic tissue associated with either Arnold s nerve CN X or Jacobsen s nerve CN IX Typically the tumor enlarges to fill the middle ear space and to envelope the ossicles The tympanic membrane may be displaced laterally but rarely


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