23 April 2022: Articles
A Rare Case of an Intracranial Dermoid Cyst with Atypical Appearance on Computed Tomography and Magnetic Resonance Imaging
Challenging differential diagnosis, Rare diseasePatricia Delgado-Muñoz1ABCDEF*, Maria S. Oliver-Ricart2DEF, Eduardo J. Labat-Alvarez1ABCDEF
Am J Case Rep 2022; 23:e935115
BACKGROUND: Dermoid cysts are rare benign intracranial tumors that usually present classic computed tomography (CT) and magnetic resonance imaging (MRI) characteristics, allowing for relatively simple diagnostic confirmation. Atypical imaging features can occur due to their diverse ectodermal-derived content, which can result in a diagnostic dilemma. Making an accurate diagnosis is essential for adequate management.
CASE REPORT: We present a case of a 39-year-old woman with past medical history of increased blood pressure, presenting with worsening headaches non-refractory to medication. Imaging revealed an extra-axial lesion within the midline posterior fossa with an occipital transdiploic linear channel. The lesion was T2 profoundly hypointense on brain MRI, and prominently hyperdense on non-contrast CT scan. Catheter angiography excluded vascular etiology. After complete lesion resection, results of the histopathologic examination were consistent with a dermoid cyst. Dermoid cysts that are hyperdense on CT and hypointense on T2-WI are extremely rare.
CONCLUSIONS: Complete surgical resection is the treatment of choice for most dermoid cysts. Atypical radiologic features, in an already rare intracranial tumor, can delay correct diagnosis and management. Recognition of these findings is therefore important for adequate imaging analysis of these lesions.
Keywords: Dermoid Cyst, Magnetic Resonance Imaging, multidetector computed tomography
Among all primary intracranial tumors, dermoid cysts comprise less than 1% of cases. They are benign congenital inclusion cysts that embryologically develop from ectodermal tissue. Midline sellar, parasellar, frontonasal, and posterior fossa are the most common locations. [1–4] Due to their diverse ectodermal derived content, including apocrine glands, sebaceous glands, hair follicles and/or teeth, their imaging appearance may vary. [1,5,6] However, almost all dermoid cysts present with classic lipid containing characteristics such as hypodense appearance on CT and hyperintensity on T1–WI with no contrast enhancement [1–4] and a heterogeneous signal intensity on T2–WI . We present a case of an intracranial dermoid cyst with atypical imaging features.
A 39-year-old woman with past medical history of increased blood pressure was referred to our institution due to a possible posterior fossa hematoma as per head computed tomography (CT) performed at an outside hospital. Further history revealed gradual onset of headaches for 6 months with recent worsening and non-refractory to NSAIDs. The patient denied nausea, vomiting, changes in vision, or fever. No history of recent trauma was reported. At physical examination there were no neurologic deficits.
MRI (Figure 1) showed a well-defined T1 hyperintense and T2 profoundly hypointense extra-axial lesion within the midline posterior fossa, demonstrating susceptibility artifact, no restricted diffusion, and no contrast enhancement, measuring 4.0 cm transverse by 3.8 cm AP by 4.9 cm CC. The lesion resulted in a local mass effect upon adjacent structures with partial compression of the vermis and bilateral cerebellar hemispheres, and subsequent tonsillar herniation. Partial compression of the fourth ventricle and fourth ventricular outflow tract caused mild supratentorial obstructive hydrocephalus. A transdiploic linear channel was seen on MRI.
Additionally, a partial empty sella and bilateral optic nerve disc flattening were present, as can be seen with increased intracranial pressure. On non-contrast CT scan (Figure 2) the lesion showed homogenous hyperdensity with better delineation of the overlying midline occipital transdiploic channel. A profoundly hypodense focus within the transdiploic channel near the lesion measured −13 Hounsfield units, which, given its increased signal intensity on MRI, could represent a small focus of fat. There appeared to be mild relative thickening of the occipital bone. To exclude a vascular etiology, catheter angiography (Figure 3) was performed, which showed no evidence of a vascular lesion or of neoplastic/tumoral blush.
The patient underwent suboccipital craniotomy for lesion re-section, with a preoperative diagnosis of a posterior fossa brain mass. Histopathologic examination found cholesterol clefts and hair shafts, as well as luminal lamellated keratin flakes. Additionally, foreign-body type (multinucleated) giant cell reaction and pigment-laden macrophages where identified. These findings are consistent with a dermoid cyst (Figure 4).
The patient successfully recovered.
Clinically, dermoid cyst are usually asymptomatic. Sometimes symptoms may present, including headaches and seizures, likely attributed to the associated mass effect. If there is dermoid cyst rupture, signs of chemical meningitis may be present [1,2]. The patient in this case presented with chronic headaches, which can occur with a dermoid cyst but is non-specific.
Dermoid cysts are extremely rare, accounting for only 0.7% of all intracranial tumors. They arise from ectodermal tissue by cell inclusion into the neural tube before the 6th week of embryogenesis [1,2]. For this reason, their most common locations are midline, mainly found at sellar, parasellar, frontonasal, and posterior fossa regions [1–4]. The imaging characteristics depend on their internal components. Being of ectoderm origin, they have a capsule of simple epithelium and their lining may be composed of hair follicles, sebaceous glands, apocrine glands, and/or teeth . On imaging, they are characteristically well-defined lesions with a wall than may be calcified. The lipid component gives it its typical appearance, being mainly hypodense on CT, and on MRI showing hyperintensity on T1–WI and heterogeneity or hyperintensity on T2–WI. Fat-suppressed images may help confirm the diagnosis. Enhancement is not common. Fast or abundant glandular secretions and epithelial desquamation may result in dermoid growth and rupture, which would present on imaging as scattered droplets of T1 hyperintensity [1,4]. This patient presented a typical midline extra-axial posterior fossa location with well-defined margins, but with prominent hyperintensity on CT. Additionally, although being hyperintense on T1–WI, as expected, it was profoundly hypointense on T2–WI. Dermoid cysts that are hyperdense on CT and hypointense on T2WI are extremely rare. These imaging characteristics may be related to lipid saponification, keratinized debris, suspended microcalcifications, liquefied cholesterol, increased protein, and/or hemosiderin due to prior internal hemorrhage . Another imaging feature in this case was a transdiploic channel that appeared to connect the lesion to the extracranial occipital soft tissues. Dermoid cysts in pediatric patients may have a sinus tract, usually found at an early age because it can increase the risk of recurrent meningitis . Even in an adult, a midline extra-axial mass with an associated sinus tract should prompt including a dermoid cyst in the differential diagnosis, even when found with atypical imaging features and at an atypical age.
The differential diagnosis for a dermoid cyst includes epidermoid cysts, lipomas, and craniopharyngiomas [1,4]. An epidermoid cyst would most commonly show similar density to cerebrospinal fluid on CT and MRI imaging, and an off-mid-line location. Even if presenting as a rare hyperdense epidermoid cyst, restricted diffusion would be expected on MRI . Lipomas present with homogenous fat signal characteristics in both CT and MRI. Craniopharyngiomas show strong hyper-intensity on T2-weighted images and are enhanced on post-contrast sequences . In our case, the possibility of a vascular malformation lesion also had to be excluded due to its profound hypointensity on T2–W1. Post-contrast images and digital subtraction angiography showed no evidence of a vascular lesion.
Making an accurate diagnosis is essential for proper management, with complete surgical resection being the treatment of choice for most dermoid cysts.
Dermoid cysts are intracranial tumors with characteristic imaging features. We present a case of an intracranial dermoid cyst, which is a baseline rare intracranial tumor, with atypical imaging characteristics on both CT and MRI. Knowledge of these uncommon radiologic features is therefore important in the imaging analysis of these lesions.
FiguresFigure 1.. Brain MRI showing a well-circumscribed lesion at the midline posterior fossa, which is profusely hypointense on T2-weighted sequences and hyperintense on T1-weighted sequences, without frank contrast enhancement. A transdiploic channel (arrow) is seen. There is associated mild supratentorial obstructive hydrocephalus. (A, B) T2-weighted axial images, (C) T1-weighted axial image, (D) T1-weighted sagittal image, (E) T1-weighted post-contrast axial image. Figure 2.. Head CT scan without contrast administration showing a midline posterior fossa homogenously hyperdense lesion with an overlying transdiploic channel (arrow). (A) Brain window CT axial image, (B, C) bone window CT axial images. Figure 3.. Digital subtraction angiography (DSA) images of the posterior circulation showing no evidence of a vascular lesion or of neoplastic/tumoral blush. There is inferior displacement of the left posterior inferior cerebellar artery. (A) Right vertebral artery injection, (B) left vertebral artery injection. Figure 4.. Hematoxylin and eosin stains with (A) 40×, (B, D) 100×, and (C) 200× magnification showing cholesterol clefts (black arrows) and hair shafts (blue arrows), as well as luminal lamellated keratin flakes. Additionally, foreign-body type (multinucleated) giant cell reaction (C) and pigment-laden macrophages are shown (D).
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2.. Brown JY, Morokoff AP, Mitchell PJ, Gonzales MF, Unusual imaging appearance of an intracranial dermoid cyst: Am J Neuroradiol, 2001; 22; 1970-72
3.. Matthys MK, Long SS, Huisman TAGM, Posterior fossa dermoid cyst with a sinus tract and restricted diffusion on MR imaging: Value of structural imaging findings and signal characteristics: J Neuroradiol, 2012; 39(2); 134-35
4.. Kumaran SP, Srinivasa R, Ghosal N, Unusual radiological presentation of intracranial dermoid cyst: A case series: Asian J Neurosurg, 2019; 14(1); 269-71
5.. D’Amore A, Borderi A, Chiaramonte R, CT and MR studies of giant dermoid cyst associated to fat dissemination and the cortical and cisternal cerebral spaces: Case Rep Radiol, 2013; 2013; 239-58
6.. Smirniotopoulos JG, Chiechi MV, Teratomas, dermoids, and epidermoids of the head and neck: Radiographics, 1995; 15(6); 1437-55
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