Petrous bone epidermoid cyst caused by penetrating injury to the external ear: Case report and review of literature

Abstract

Epidermoid cysts are histologically benign, slow-growing congenital neoplasms of the central nervous system that may arise from retained ectodermal implants. The epidermoid lesions are generally caused during the 3(rd) to 5(th) week of gestation by an incomplete cleavage of the neural tissue from the cutaneous ectoderm, though it can also happen later in life due to introduction of skin elements by skin puncture, trauma or surgery. We present this unique case of a petromastoid epidermoid cyst associated with ipsilateral cerebellar abscesses, presenting 20 years after a penetrating trauma to the external auditory canal. Radical excision of both lesions and revision of the previous fistulous tract was performed. We present the diagnostic challenge and the operative treatment of this unique case, which to our knowledge is the first where an epidermoid cyst and an adjacent brain abscess occurred as a result of a single traumatic event.

Keywords: Epidermoid cyst; penetrating trauma; petrous bone; surgical treatment.

Figure 1

CT scan of the brain without contrast demonstrating a well-defined hyperdense mass occupying the right petromastoid region. Adjacent cerebellar edema compressing the IV ventricle is also shown

Figure 2

(a) Axial T2-weighted MR imaging demonstrating spaceoccupying lesion filling the right mastoid air cells that is heterogeneously hyperintense and associated with vasogenic hyperintense edema in the right cerebellum; (b) T1-weighted MR imaging with gadolinium contrast enhancing demonstrating no contrast enhancement of the mastoid lesion and two ring enhancement lesions (abscesses) in the right cerebellum with mass effect on the fourth ventricle and right side of the brainstem

Figure 3

(a) Intraoperative view of the epidermoid cyst in the mastoid region; (b) Gross view of the epidermoid cyst after radical resection

Figure 4

(a) The superior arrow indicates the opening of the fistulous tract (arrow) into the mastoidal area, and the facial nerve is shown between dotted lines; (b) Intraoperative image of the vascularized temporalis flap to cover the fistula over the external auditory canal as well as the middle ear (arrow)

Figure 5

(a) Low power (40×) (a) and high power (200×) (b) H and E staining images demonstrating the characteristic keratinized stratified squamous epithelium lining (arrow) of the epidermoid cyst along with a superficial multilayer keratinaceous surface and keratin debris. In 5b the details of the anucleated cell ghosts (*) is seen better appreciated

Figure 6

T1-weighted, gadolinium enhanced MR imaging axial view, obtained six weeks after surgery showing complete radical excision of the lesions, and healing after antibiotic therapy