mucosal melanoma accounts for 1% of all melanoma of the head and neck , with most cases in the nasal and oral cavity . a malignant melanoma in the eustachian tube is so rare that only 6 cases have been reported until recently ( 1 - 5 ) . to the best of our knowledge , there was no report of the computed tomography ( ct ) and magnetic resonance imaging ( mri ) findings of a malignant melanoma in eustachian tube , which extended to nasopharynx and middle ear cavity simultaneously . here , we present the magnetic resonance ( mr ) imaging findings of a primary amelanotic melanoma of the eustachian tube with unusual extension . a 51-year - old woman with no significant medical history presented at a local otolaryngologist with right ear fullness . only chronic , her symptom did not improve and an otorhinolaryngologic examination revealed a dark colored mass behind the tympanic membrane . ct showed a soft tissue mass in the middle ear cavity , which was widening and eroding the bony eustachian tube ( fig . mri revealed an elliptical shaped well - defined mass , located in the eustachian tube and extending to the orifice in the nasopharynx to the middle ear cavity . 1b , c ) and high signal intensity on t2-weighted image with moderate homogeneous enhancement following the administration of contrast material ( fig . 1d , e ) . neither an enlarged retropharyngeal node , evidence of head and neck melanoma , or systemic abnormalities was found . although , a hematoxylin - esosin stain did not reveal tumor cells containing melanin ( fig . 1h ) , and s-100 on immunohistochemical stainings . of the results of the histopathologic study suggest an amelanotic melanoma as the final diagnosis . during her work up melanoma is composed of a proliferation of melanocytes , which derive from the neural crest and subsequently migrate into the nasal mucosal surface with an ectodermal origin . mucosal melanomas of the head and neck mostly occur between the fifth and seventh decades of life , with a slight male predominance , equally involving the sinonasal or oral mucosa ( 6 ) . unusually , the malignant melanoma can be found in the nasopharyngeal opening of the eustachian tube ( 1 , 2 , 5 ) , restricted to eustachian tube ( 4 ) , and extending from the middle ear cavity to the nasopharynx ( 3 ) . the etiology of mucosal melanoma is still unknown at present ( 7 ) . ct is useful to determine the bone change , but it is difficult to make a differential diagnosis by ct alone because bone destruction is negligible and the ossicles are intact in malignant melanoma of the middle ear cavity ( 8) . moreover , the inferior soft - tissue resolution of ct make the diagnosis more difficult ( 5 ) . mr imaging is more useful for evaluation of the melanoma in the extension of the tumor and the components of the mass . even though a physical examination revealed only a middle ear cavity mass , the tumor could extend from the eustachian tube to the nasopharynx . the signal intensity of the lesion largely depends on the concentration and distribution of melanin in the tumor ( 9 ) . characteristic mr imaging findings of high signal intensity on t1-weighted image and low signal intensity on t2-weighted image are due to higher content of melanin in the tumor ( 10 ) . conversely , in cases of an amelanotic melanoma , the signal intensity of the mass can demonstrate low signal intensity on t1-weighted images and high signal intensity on t2-weighted images ( 8 , 11 ) . in the presenting case , we found the erosion of the bony eustachian tube on ct and a well demarcated tumor extension on mri . however , the signal intensity of the tumor did not show the characteristic signal intensity of melanoma , and hence , we can hardly consider the malignant melanoma on mr imaging . in considering the differential diagnoses of the lesion along the eustachian tube extending from the middle ear cavity and nasopharynx squamous cell carcinoma usually originates from the rosenmuller fossa and is limited by its cartilaginous portion and pharyngobasilar fascia . a glomus tumor has a unique salt - and - pepper pattern and serpentine flow void with intense enhancement . lastly , lymphoma may involve the eustachian tube , but it often shows bulky mass and lymphadenopathy ( 5 , 11 , 12 ) . one should have to consider the malignant melanoma as a differential diagnosis , if we found the following characteristics : ( 1 ) a soft tissue mass in the eustachian tube extending from the middle ear cavity to the nasopharynx , even if it does not shows typical high signal intensity on t1 weighted image ; ( 2 ) an erosion of the bony eustachian tube .
we report a case of malignant melanoma of eustachian tube with extension to the middle ear cavity and nasopharynx in a 51-year - old woman who presented with right ear fullness . 
 computed tomography showed a soft tissue mass in the middle ear cavity and causedthe widening and eroding of the bony eustachian tube . 
 magnetic resonance imaging showed well enhancing mass in eustachian tube extending nasopharynx to middle ear cavity . 
 a biopsy of the middle ear cavity mass revealed a malignant amelanotic melanoma .