Ruptured intracranial dermoid cyst.Intracranial dermoid cystic tumors account for <1% of all intracranial masses. Dermoids are nonneoplastic, congenital ectodermal inclusion cysts that contain varying amounts of ectoderm derivatives to include apocrine, sweat, and sebaceous cysts as well as hair follicles, squamous epithelium, and possibly teeth. They are not to be confused with an epidermoid cyst, which contains only squamous epithelium. Teratomas, although similar in some respects, are a separate entity. Teratomas are true neoplasms that contain tissue from all three embryonic germ cell layers (1).
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Dermoid cystic tumors arise from the inclusion of ectodermally committed cells at the time of neural tube closure during the third to fifth week of embryogenesis. These lesions are slow growing due to the active production of hair and oils from the internal dermal elements (2). The presentation of dermoid tumors is quite variable. Occasionally they are incidental findings discovered on brain computed tomography (CT) or magnetic resonance imaging (MRI) for otherwise unrelated clinical complaints, or they are discovered during imaging investigation of unexplained headaches, seizures, and rarely olfactory delusions (3, 4). When dermoid cystic tumors rupture and spread their contents into the ventricles and subarachnoid and/or subdural spaces, the most common clinical presentation is that of headache and seizures. Headache may be the consequence of compression of adjacent neural structures, chemical meningitis from cyst content irritation, or perhaps the effects of hydrocephalus if present.
A 46-year-old man, without significant past medical history, presented for the evaluation of constant unrelenting headaches of 1 month's duration. The headaches had a waxing and waning course with sporadic episodes of photophobia. The patient complained of severe right trigeminal nerve-type pain. The patient had no complaints of nausea, vomiting, altered mental status, or seizures. On presentation, vital signs were normal. Laboratory evaluation revealed only a mild leukocytosis. No focal neurologic deficits were identified. An initial CT scan of the brain without contrast material demonstrated a 2.4 cm diameter extra-axial fat-containing mass with scattered intralesional calcific deposits centered near the anterior clinoid process and overlying the superior orbital fissure (Figure 1). Portions of the mass were contained within both the anterior and middle cranial fossae. Scattered fat-containing droplets were disseminated throughout the subarachnoid space. A subsequent MRI scan showed additional imaging features characteristic of a ruptured dermoid cystic tumor (Figure 2).
In the operating room, a craniotomy flap was elevated for exposure. The dura was then opened along the sphenoid ridge for visualization of the skull base. Microscopic dissection clearly determined the mass to be extra-axial, growing from the anterior clinoid region superiorly toward the brain. Arachnoid adhesions were released and the sylvian fissure opened proximally, exposing the lesion (Figure 3). A clear fat plane existed between the tumor and the brain parenchyma, and the borders were separated. The mass was too large for en bloc resection. It was incised and found to be amorphous and amenable to suction. Pathology evaluation of the submitted tissue confirmed the diagnosis of a dermoid cystic tumor (Figure 4).
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The patient's postoperative course was uneventful. An MRI scan of the brain obtained 4 months after resection showed minimal persistent intraventricular fat droplets without recurrence or discernible complications of the resection. The patient has resumed most normal activities.
Intracranial dermoid cystic tumors are rare, benign, slow-growing masses. They are most often found in a sellar or parasellar location as well as the frontonasal region and frequently reside near the skull base. Intracranial dermoids can also be found in the posterior cranial fossa within or in close proximity to the fourth ventricle. These lesions can also be found in the pineal gland fossa, in addition to a number of other less frequent intracranial sites (4--6).
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Symptoms typically are ascribed to mass effect created on adjacent intracranial structures. If rupture occurs, aseptic chemical meningitis may ensue with profound irritative effects from the disseminated cholesterol debris. Chemical meningitis is a relatively rare development and is reported in approximately 7% of cases of dermoid tumor rupture (1, 5). Chemical meningitis may elicit transient cerebral ischemia secondary to vasospasm with complicating infarction that may result in the death of the patient. Morbidity may also be related to chemical arachnoiditis (7). Symptom onset typically does not occur at the time of rupture, since the irritative effects of the spilled contents require time to develop, but may be delayed from 3 months to 6.5 years after rupture (3).
Dermoid cystic tumor rupture usually occurs spontaneously; however, cases of rupture secondary to closed head trauma or iatrogenic surgical complications have been reported (5). Supratentorial dermoids often present in the second or third decades of life, while posterior fossa dermoids typically present in the first decade of life as a consequence of mass effect exerted on the fourth ventricle with resulting hydrocephalus (3). Posterior fossa cystic tumors may have visible occipital scalp dimples or sinus tracts. If present, these are usually discovered in infancy. A fistulous sinus tract may lead to recurrent bouts of bacterial meningitis (1).
Imaging features of intracranial dermoid tumors on brain CT scans are virtually pathognomonic. These lesions will have internal density characteristics consistent with fat (negative Hounsfield units) (Figure 1), although density values greater than fat may be encountered depending on the nature of an individual tumor's contents. The dermoid wall is typically seen and can calcify. Occasionally the wall will at least partially enhance following the administration of CT-iodinated contrast material. On MRI scans, dermoids will be hyperintense (bright) on T1weighted imaging and heterogenous on T2-weighted imaging (Figure 2). If the internal fat content is relatively low, the lesion will reveal cerebrospinal fluid--like signal intensity. In such cases, fluid attenuation inversion recovery (FLAIR) is useful, in that the fat will appear hyperintense (bright) on a background of suppressed fluid signal (dark). On MRI, fat constituents create a so-called "chemical shift" artifact due to misregistration of the signal in the frequency-encoded direction. This can be particularly useful in diagnosing these lesions preoperatively. When a dermoid tumor ruptures, fat droplets--appearing hypodense on CT or Tl hyperintense on MRI--may be seen scattered and floating within the nondependent portions of the ventricular system and/or subarachnoid space. This is considered a classic imaging feature of these lesions. In the setting of complicating chemical meningitis, intense pial and ventricular ependymal enhancement may be detected after the administration of MRI gadolinium contrast (1-3).
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Although the imaging appearance of dermoid tumors is characteristic, several other intracranial lesions must be considered in the differential diagnosis, such as epidermoids, teratomas, lipomas, craniopharyngiomas, and occasionally arachnoid cysts. A review of all available CT and MRI images often allows the radiologist to offer an accurate preoperative diagnosis.
Surgical care focuses on complete microsurgical resection of the mass and wall. If the tumor has not ruptured preoperatively, great care is made to avoid spilling the contents in the surgical bed. Patients typically do well after operative intervention. Recurrence is rare but is more common if there are retained portions of the tumor wall. Rare reports describe the development of squamous cell carcinoma in retained remnants of a dermoid cystic tumor wall (3, 8).
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M. Jordan Ray, MD, David W. Barnett, MD, George J. Snipes, MD, Kennith F. Layton, MD, and Michael J. Opatowsky, MD
From the Departments of Radiology (Ray, Layton, Opatowsky), Neurosurgery (Barnett), and Pathology (Snipes), Baylor University Medical Center at Dallas.
Corresponding author: M. Jordan Ray, MD, Department of Radiology, Baylor University Medical Center at Dallas, 3500 Gaston Avenue, Dallas, TX 75246 (e-mail: Mjordan.email@example.com).