Two cases of incidental epidermoid cysts: sphenoid sinus and temporal bone.

Abstract

Epidermoid cysts or tumors are uncommon. When they do occur, they are usually large at presentation, and the initial symptoms usually involve the cranial nerves. Congenital epidermoids are believed to arise as a result of cellular dysfunction during embryogenesis, which leads to an abnormal migration of ectodermal cells. We present 2 cases of epidermoids that were identified incidentally at our institution during radiologic evaluations of head trauma; one was found in the sphenoid sinus and the other in the temporal bone. Both patients were treated surgically. We review the pathogenesis, diagnosis, and imaging characteristics of these epidermoids.

Introduction

Epidermoid tumors are uncommon but still part of the differential diagnosis of intracranial masses. According to the literature, these masses account for approximately 1% of all intracranial tumors. (1) Epidermoids of the sphenoid sinus are exceedingly rare, having been described only twice previously in the literature. (2,3)

To the best of our knowledge, no report of an incidental sphenoid sinus epidermoid has appeared in the literature. We present one such case as well as another case of an incidental epidermoid tumor that was found in the temporal bone. Neither patient had any evidence of an epidermoid by history or physical examination.

Case reports

Patient 1. A 28-year-old man, a prisoner, had been evaluated at another facility after he had fallen and hit his head on a toilet. Computed tomography (CT) at that facility showed a nonenhancing mass occupying the right sphenoid sinus with bony expansion and erosion into the pituitary fossa. The patient was transferred to our facility and evaluated by neurosurgery. He was obtunded on arrival and subsequently intubated.

Magnetic resonance imaging (MRI) of the head identified an expansile mass in the right sphenoid sinus with low to intermediate intensity on T1-weighted imaging (figure 1, A) and high intensity on T2-weighted imaging (figure 1, B). The lesion abutted the right medial temporal lobe, the right internal carotid artery, and the basilar artery.

[FIGURE 1 OMITTED]

The patient's medical history and physical examination findings (other than the head injury and its effects) were unremarkable. An endocrinology investigation found no evidence of pituitary dysfunction.

The patient was taken to the operating room for biopsy of the sphenoid sinus mass. On gross inspection, the surface of the mass resembled inspissated secretions. Frozen-section analysis identified a stratified squamous epithelial lining and keratin debris. The patient recovered from his head injury and was returned to the corrections facility.

The patient was later brought back to our institution for removal of the epidermoid, which was accomplished with an image-guided endoscopic sphenoidotomy and marsupialization of the lesion. The final pathology report identified the mass as keratin debris with focal acute inflammatory exudate. The patient had an uneventful postoperative course, and at the 6-month follow-up he was doing well.

Patient 2. A 53-year-old man was hanging drywall at a construction site when a piece of it fell and struck him on the head. He presented to the emergency department complaining of headache and dizziness. He denied any previous neurologic symptoms.

CT of the head detected no evidence of an acute intracranial process. However, it did reveal the presence of a lesion in the left temporal bone. The lesion had eroded the lateral wall of the mastoid and epitympanum and extended intracranially. A follow-up CT of the temporal bone showed a nonenhancing mass, which did not involve the ossicles or labyrinth (figure 2, A). MRI demonstrated a nonenhancing mass with intermediate signal intensity on T1-weighted imaging and high intensity on T2-weighted imaging. MRI also showed that the mass abutted the parietal and temporal lobes of the brain in the absence of any intervening bone.

[FIGURE 2 OMITTED]

On further questioning, the patient denied a history of ear disease, hearing loss, otorrhea, or otalgia, and findings on the physical examination were unremarkable. The mass was biopsied, with frozen-section analysis being indeterminate. Permanent sections were reported as "acellular keratinous debris" (figure 2, B).

A combined approach for excision was undertaken. We performed a mastoidectomy with neurosurgery, approaching via the middle cranial fossa. The patient's postoperative course was complicated by an infection at the lumbar drain site, which was treated with antibiotics.

Discussion

Incidental epidermoids can be quite large at presentation, owing to their slow growth and benign nature. They can arise anywhere along the neuraxis. Intracranial growth is more common than intraspinal growth. The most common location is the cerebellopontine angle, where epidermoids account for approximately 9% of all tumors. (4) There have also been reports of epidermoids occurring at sites of trauma, usually several years after the traumatic event (5). Epidermoids are distinct from dermoid cysts in that they do not contain skin appendages or mesoderm elements such as hair and sebaceous glands. (6)

An epidermoid that involves the middle ear and temporal bone is often called a cholesteatoma. Epidermoids that arise outside this area are believed to be congenital, whereas cholesteatomas can be either congenital or acquired. (7) Primary acquired cholesteatomas occur secondary to the development of a tympanic membrane retraction pocket, and secondary acquired cholesteatomas arise as a sequela of chronic middle ear disease. The lesion in our patient 2 spared the middle ear and appeared to originate in the temporal bone superior and posterior to the antrum of the mastoid.

Congenital cholesteatomas present in the anterosuperior mesotympanum. They may cause conductive hearing loss with or without involving the tympanic membrane. Their etiology has been debated for years. Olszewska et al published a thorough review of their pathogenesis, including past and present theories. (7) One interesting theory involves the persistence of a remnant of the epidermoid formation in the anterior superior quadrant of the middle ear. (8) The epidermoid formation normally disappears by the 33rd week of gestation. It is not known why this fetal tissue persists or how it transforms, if indeed it does, into a cholesteatoma. According to another theory, epithelial cells migrate during embryogenesis from the external auditory canal to the middle ear. (9) A third and newer theory, called the acquired inclusion theory, suggests that under normal pathologic conditions, the tympanic membrane, while retracted onto the malleus handle and neck, leaves behind squamous epithelial cells that eventually develop into an inclusion cholesteatoma. (10)

Most patients presenting with intracranial epidermoids are in their third or fourth decade of life. (1,4) As a result of the cyst's slow growth and benign nature, signs and symptoms manifest after years of growth. Findings at presentation vary; they may include cranial nerve deficits, headache, visual changes, and even seizures. It is believed that the latter occur when a cyst ruptures. In a retrospective review of epidermoids of the cerebellopontine angle, deSouza et al reported that VIIth cranial nerve palsy was the most common initial sign (followed by unilateral heating loss), and headache was the most common symptom. (4) Some years later, Mohanty et al reported that trigeminal neuralgia was the most common initial finding. (11)

Congenital cholesteatomas of the middle ear present differently in that most patients are in their first decade of life. The presenting symptom is hearing loss. Congenital lesions may also be found incidentally during a routine physical examination. (12) Absence of previous ear disease, surgery, or trauma is necessary to support the congenital theory of origin.

In a very few cases, epidermoids have undergone malignant transformation. (5,13,14) It is interesting that these transformations have occurred at the same site where a previous benign epidermoid had been removed years earlier.

Both CT and MRI can suggest a preoperative diagnosis. Epidermoid tumors do not enhance on CT because of their lack of vascularity, so MRI should be performed to augment CT findings; epidermoid tumors are hypointense on T1-weighted MRI and hyperintense on T2-weighted MRI. Occasionally, MRI has difficulty distinguishing an epidermoid from an arachnoid cyst; this problem can be overcome with a fluid-attenuated inversion recovery (FLAIR) MRI when an epidermoid is hyperintense. (15)

Treatment options for epidermoids are primarily surgical. The tumor's lack of a blood supply eliminates radiation as an option. Close follow-up is necessary to look for potential recurrence; the rare nature of this tumor makes it difficult to ascertain its recurrence rate.

The temporal bone tumor in our patient 2 was amenable to complete resection given its location and proximity to surrounding structures. Based on his age, we believe his tumor was not a congenital cholesteatoma.

The sphenoid sinus tumor in our patient 1 represented a greater threat in that the only surgical option was transnasal endoscopic sphenoidotomy with marsupialization of the tumor. The tumor's location between the carotid artery, optic chiasm, pituitary gland, and cavernous sinus made en bloc resection impossible. Therefore, he will need to undergo periodic endoscopic evaluation and debridement. To the best of our knowledge, his case is only the third case of a sphenoid sinus epidermoid reported in the literature and the only one of the 3 that was detected incidentally.

References

(1.) Ulrich J. Intracranial epidermoids. A study on their distribution and spread. J Neurosurg 1964;21:1051-8.

(2.) Sani S, Smith A, Leppla DC, et al. Epidermoid cyst of the sphenoid sinus with extension into the sella turcica presenting as pituitary apoplexy: Case report. Surg Neurol 2005;63:394-7.

(3.) Ohta S, Nishizawa S, Ryu H, et al. Epidermoid tumor in the sphenoid sinus--case report. Neurol Med Chir (Tokyo) 1997;37:350-3.

(4.) deSouza CE, deSouza R, da Costa S, et al. Cerebellopontine angle epidermoid cysts: A report on 30 cases. J Neurol Neurosurg Psychiatry 1989;52:986-90.

(5.) Toglia JU, Netsky MG, Alexander E Jr. Epithelial (epidermoid) tumors of the cranium. Their common nature and pathogenesis. J Neurosurg 1965;23:384-93.

(6.) Leech RW, Olafson RA. Epithelial cysts of the neuraxis. Presentation of three cases and a review of the origins and classification. Arch Pathol Lab Med 1977;101:196-202.

(7.) Olszewska E, Wagner M, Bernal-Sprekelsen M, et al. Etiopathogenesis of cholesteatoma. Eur Arch Otorhinolaryngol 2004;261: 6-24.

(8.) Michaels L. An epidermoid formation in the developing middle ear: Possible source of cholesteatoma. J Otolaryngol 1986;15: 169-74.

(9.) Aimi K. Role of the tympanic ring in the pathogenesis of congenital cholesteatoma. Laryngoscope 1983;93:1140-6.

(10.) Tos M. A new pathogenesis of mesotympanic (congenital) cholesteatoma. Laryngoscope 2000;110:1890-7.

(11.) Mohanty A, Venkatrama SK, Rao BR, et al. Experience with cerebellopontine angle epidermoids. Neurosurgery 1997;40:24-9.

(12.) Darrouzet V, Duclos JY, Portmann D, Bebear JP. Congenital middle ear cholesteatomas in children: Our experience in 34 cases. Otolaryngol Head Neck Surg 2002;126:34-40.

(13.) Link MJ, Cohen PL, Breneman JC, Tew JM Jr. Malignant squamous degeneration of a cerebellopontine angle epidermoid tumor. Case report. J Neurosurg 2002;97:1237-43.

(14.) Asahi T, Kurimoto M, Endo S, et al. Malignant transformation of cerebello-pontine angle epidermoid. J Clin Neurosci 2001;8: 572-4.

(15.) Dutt SN, Mirza S, Chavda SV, Irving RM. Radiologic differentiation of intracranial epidermoids from arachnoid cysts. Otol Neurotol 2002;23:84-92.

From the Department of Otolaryugology-Head and Neck Surgery, University of Missouri School of Medicine, Columbia.

Reprint requests: Derek K. Hewitt, MD, Department of Otolaryngology-Head and Neck Surgery, University of Missouri School of Medicine, One Hospital Dr., Columbia, MO 65212. Phone: [phone]; fax: [phone]; e-mail: HewittD@health. missouri.edu

Derek K. Hewitt, MD, MPH; William C. Kinney, MD, MHA