CHAPTER
6
CYSTIC LESIONS
6.1 | Arachnoid Cyst |
Case History
A 56-year-old man presented with a headache, which was thought to be chronic tension headache with normal neurological examination. An incidental finding was noted on the brain MRI.
Diagnosis: Arachnoid Cyst
Images 6.1A–6.1D: Axial T2-weighted images (6.1A, 6.1B) and coronal (6.1C) and sagittal T1-weighted image (6.1D) demonstrate a large cystic, extraaxial lesion in the middle cranial fossa; it follows the CSF signal on all pulse sequences.
Introduction
Arachnoid cysts (ACs) are benign sacs filled with cerebrospinal fluid (CSF) that are formed between the inner and outer layers of the arachnoid. They are usually congenital abnormalities caused by a failure of the arachnoid membrane to fuse and dysgenesis of the embryonic development of subarachnoid space, allowing for the flow of CSF into a cleft beneath the arachnoid.
These are typically congenital but can develop after trauma, subarachnoid hemorrhage, meningitis, or mastoiditis.
Clinical Presentation
Most cysts are incidental findings, but can cause symptoms due to compression of the brainstem, hypothalamus, or optic chiasm. Large cysts may cause hypoplasia of the adjacent brain structures.
ACs are more common in males than females.
Radiographic Appearance and Diagnosis
On CT and all MRI sequences, they follow the signal intensity of CSF. They are most commonly confused with epidermoid cysts, but ACs have smooth margins, in contrast to epidermoid cysts, which have uneven borders.
These can cause bone remodeling and macro-crania.
They are most commonly found in the middle cranial fossa outside of the temporal lobe.
The Galassi classification system is used to describe middle cranial fossa ACs:
Type I: small size, located in the anterior temporal lobe and exerts no mass effect
Type II: medium-size cysts located in the anterior and middle temporal fossa can cause displacement of the temporal lobe.
Type III: constitutes a large oval or round cyst that fills the entire temporal fossa and exerts large mass effect
About 10% to 15% of ACs are found in the suprasellar region. The can also be found in the cerebral convexity, cisternal spaces (quadrigeminal or suprasellar cistern), cerebellopontine angle, posterior fossa, the interhemispheric fissure, within the ventricle and the spinal canal.
Treatment
Symptomatic ACs can be surgically drained by either craniotomy (fenestration or excision) or placement of a cystoperitoneal shunt.
Images 6.1E and 6.1F: Sagittal T1-weighted image and axial T2-weighted image demonstrate a suprasellar cyst. Images 6.1G and 6.1H: Sagittal T1-weighted image and axial T2-weighted image demonstrate an interhemispheric cyst.
Images 6.1I and 6.1J: Sagittal T1-weighted image and axial T2-weighted image demonstrate a posterior fossa cyst. All cysts follow the isointense CSF signal on all pulse sequences.
References
1. Pradilla G, Jallo G. Arachnoid cysts: case series and review of the literature. Neurosurg Focus. February 2007;22(2):E7.
2. Westermaier T, Schweitzer T, Ernestus RI. Arachnoid cysts. Adv Exp Med Biol. 2012;724:37–50.
3. von Wild K. Arachnoid cysts of the middle cranial fossa. Neurochirurgia (Stuttg). November 1992;35(6):177–182.
4. Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239(3):650–664.
6.2 | Colloid Cyst of Third Ventricle |
Case History
A 34-year-old man developed severe headaches and transient visual blurring whenever he stood up after lying down. On several occasions, he lost consciousness after a particularly severe headache.
Diagnosis: Colloid Cyst of Third Ventricle
Images 6.2A–6.2C: Axial fluid-attenuated inversion recovery, postcontrast sagittal T1-weighted, and noncontrast axial T1-weighted images demonstrate a hyperintense cyst in the foramen of Monro. There is subtle enhancement around the rim of the cyst (red arrow). Image 6.2D: Gross pathology of a colloid cyst.
Introduction
Colloid cysts of the third ventricle are a type of neuroepithelial cyst. They are benign growths typically found in the anterior part of the third ventricle, adjacent to the fornix. Other benign cysts are encountered around several sites in and around the central nervous system (CNS; see Table 6.2.1).
They are uncommon, accounting for 1% to 2% of intracranial tumors; these are considered to be congenital and typically present in patients between the ages of 20 and 50 years.
Table 6.2.1 Cysts Around the Midline of the Brain and Spinal Cord
Colloid cyst of third ventricle |
Epidermoid cyst in parasellar region |
Rathke’s cleft cyst |
Epidermoid cyst in cerebellopontine angle |
Dermoid cyst in cerebellar vermis |
Ependymal cyst of cervical region |
Epidermoid cyst in thoracic canal |
Neurenteric cyst in lumbar region |
Dermoid cyst in conus |
Clinical Presentation
In the vast majority of cases, these cysts are found incidentally and are asymptomatic.
These may produce headache, papilledema, and vision changes or present with hydrocephalus and symptoms of increased intracranial pressure (ICP). It can cause transient obstruction of CSF flow through the foramen of Monro through a ball-valve mechanism. Occasionally, sudden dramatic increases in ICP can lead to a loss of consciousness or even death if the obstruction does not resolve spontaneously.
Radiographic Appearance and Diagnosis
They are filled with a variety of components including CSF, mucoid content, cholesterol, proteins, and water content. This leads to a highly variable appearance. Depending on the exact contents of the cyst it can be isointense or hyperintense to CSF on MRI.
With contrast administration, there is sometimes a rim of enhancement, perhaps representing stretched venous structures, but not solid enhancement. Neuroepithelial cysts may occur in any section of the ventricular system, and in such instances they are usually incidental findings.
Nearly all colloid cysts are found in the anterior part of the third ventricle but rarely these can be seen in the posterior part of the third ventricle, lateral ventricles, or even fourth ventricles. Colloid cysts of the third ventricle can cause enlarged lateral ventricles and even hydrocephalus.
Table 6.2.2 lists other masses near the foramen of Monro, which should be considered in the differential diagnosis of colloid cysts of third ventricle.
Table 6.2.2 Differential Diagnosis of Other Masses Arising From the Foramen of Monro
Pediatric | Adult |
Subependymal giant cell astrocytomas | Aneurysm |
Subependymal nodules in tuberous sclerosis | Cysticercus cyst |
Central neurocytoma | Meningioma |
Pilocytic astrocytoma | Lymphoma |
Choroid plexus papilloma | Intraventricular metastasis |
Glioma | Glioma |
Germinoma | Ependymal cyst |
Craniopharyngioma | Pituitary adenoma |
On immunohistochemical profile, the cysts show endodermal differentiation and their walls are lined by a columnar or cuboidal epithelium; mucin producing goblet cells in the epithelium of the colloid cyst can be stained with periodic acid-Schiff–diastase.
Treatment
Colloid cyst, although a benign tumor, is surgically challenging because of its deep midline location. Early detection and total excision of the colloid cyst carry an excellent prognosis.
Endoscopic removal of colloid cysts in the third ventricle is a safe and effective approach compared with transcallosal craniotomy. The endoscopic approach is associated with a shorter operative time, shorter hospital stay, and lower infection rate than the transcallosal approach. However, more patients treated endoscopically needed a reoperation for residual cyst.
A small number of these patients may need a transcallosal craniotomy to remove residual cysts, and this usually ensures gratifying and lasting results.
Images 6.2E and 6.2F: Axial T2-weighted and T1-weighted images demonstrate a neuroepithelial cyst in association with the frontal horn of the right lateral ventricle.
References
1. Ravnik J, Bunc G, Grcar A, Zunic M, Velnar T. Colloid cysts of the third ventricle exhibit various clinical presentation: a review of three cases. Bosn J Basic Med Sci. August 2014;14(3):132–135.
2. Desai KI, Nadkarni TD, Muzumdar DP, Goel AH. Surgical management of colloid cyst of the third ventricle—a study of 105 cases. Surg Neurol. May 2002;57(5):295–302.
3. Kumar V, Behari S, Kumar Singh R, Jain M, Jaiswal AK, Jain VK. Pediatric colloid cysts of the third ventricle: management considerations. Acta Neurochir (Wien). March 2010;152(3):451–461.
4. Abdou MS, Cohen AR. Endoscopic treatment of colloid cysts of the third ventricle. Technical note and review of the literature. J Neurosurg. 1998;89(6):1062–1068.
Unless otherwise stated, all pathology images in this chapter are from the website http://medicine.stonybrookmedicine.edu/pathology/neuropathology and are reproduced with permission of the author, Roberta J. Seidman, MD, Associate Professor.
6.3 | Epidermoid Cyst |
Case History
A 40-year-old woman presented with right facial pain. The patient was diagnosed with right trigeminal neuralgia.
Diagnosis: Epidermoid Cyst
Images 6.3A–6.3D: Axial T2-weighted, T1-weighted, diffusion-weighted, and gradient echo sequence images demonstrate a cystic lesion in the right cerebellopontine angle. The diffusion-weighted image demonstrates restricted diffusion.
Introduction
Epidermoid cysts are congenital, and mainly intracranial cysts, most commonly found near the cerebellopontine angle, parasellar regions and cranial diploë spaces, pineal region, or near foramen magnum.
They are composed of epidermal cells, which are believed to arise from embryonic epidermal rests. Mature epidermal cells are found in the center of the cyst, which frequently desquamate into the cyst center, which is also composed of keratin and cholesterol crystals. Proliferative epidermal cells line the periphery of the cyst.
They are rare, accounting for less than 1% of all intracranial tumors.
Clinical Presentation
They are often incidental findings, but may become symptomatic in patients in their 20s or 30s and cause headaches, seizures, or mass effect on surrounding structures.
Radiographic Appearance and Diagnosis
They are isointense to CSF on all MRI sequences and demonstrate restricted diffusion. There may be a thin rim of enhancement with the addition of contrast.
On gross pathology they have a smooth gray surface and friable waxy material inside. These are called “pearly tumors” due to their appearance (Image 6.3H). Microscopically, these cysts are lined by stratified squamous epithelium.
Images 6.3E–6.3G: Sagittal T1-weighted and axial T2-weighted images demonstrate a cystic lesion isointense to CSF in the suprasellar region. The diffusion-weighted image demonstrates restricted diffusion. Image 6.3H: Gross pathology of an epidermoid cyst; these cysts are known as “pearly tumors” (image credit Jensflorian).
They are similar in appearance to arachnoid cysts; however, epidermoid cysts tend to have a jagged border, unlike arachnoid cysts, which have smooth borders. Additionally, arachnoid cysts do not demonstrate restricted diffusion.
Images 6.3I–6.3L: Axial T2-weighted, fluid-attenuated inversion recovery, and pre- and postcontrast T1-weighted images demonstrate a cystic, midline lesion isointense to CSF. There is enhancement around the periphery with the addition of contrast (red arrow).
Treatment
Symptomatic cysts can be surgically excised.
References
1. Hu XY, Hu CH, Fang XM, Cui L, Zhang QH. Intraparenchymal epidermoid cysts in the brain: diagnostic value of MR diffusion-weighted imaging. Clin Radiol. July 2008;63(7):813–818.
2. Krass J, Hahn Y, Karami K, Babu S, Pieper DR. Endoscopic assisted resection of prepontine epidermoid cysts. J Neurol Surg A Cent Eur Neurosurg. March 2014;75(2):120–125.
6.4 | Ruptured Dermoid Cyst |
Case History
A 30-year-old woman presented with the sudden onset of a severe headache.
Diagnosis: Ruptured Dermoid Cyst
Image 6.4A–6.4D: Axial CT, T2-weighted, and postcontrast axial and sagittal T1-weighted images demonstrate two hypodense and hyperintense, extraaxial, globular masses over the right temporal lobe. On all sequences, the lesion has the signal characteristics of fat, and is consistent with a ruptured dermoid cyst.
Introduction
Dermoid cysts are congenital lesions believed to arise from embryonic skin tissue that remains trapped in the CNS during closure of the neural tube. Both dermoid cysts and epidermoid cysts are lined by stratified squamous epithelium. Dermoids are composed of elements of the dermis, which includes hair follicles, sweat and sebaceous glands, and epidermis, while epidermoid cysts are composed only of desquamated squamous epithelium.
They are rare, accounting for less than 0.5% of intracranial tumors.
They are often incidental findings, but when symptomatic tend to present before the age of 30.
Clinical Presentation
They occur most frequently in the cerebellopontine angle or in the midline areas of the brain, including the fourth ventricle. They are also found in the lumbosacral spinal cord where they present with a myelopathy or cauda equina syndrome.
They can gradually enlarge and cause symptoms due to mass effect on adjacent structures. Importantly, they may rupture into the subarachnoid space or ventricles, leading to a severe headache and symptoms of meningeal irritation due to chemical meningitis. This can lead to significant morbidity due to vasospasm and ischemia.
Radiographic Appearance and Diagnosis
On CT, dermoids are isodense to CSF. Calcification is common as well. On unenhanced T1-weighted images, they are hyperintense and there is no enhancement with the administration of contrast. There may be pial enhancement if there is chemical meningitis due to cyst rupture. There is a variable appearance on T2-weighted images.
Treatment
Symptomatic cysts can be surgically excised with excellent outcomes.
Images 6.4E–6.4H: Noncontrast axial T1-weighted, postcontrast sagittal T1-weighted, axial fluid-attenuated inversion recovery, and axial CT images demonstrate a hyperintense, hypodense lesion in the right posterior lateral mesencephalic cistern.
Images 6.4I and 6.4J: Sagittal T2-weighted and postcontrast fat-suppressed T1-weighted images demonstrate an intradural, extramedullary heterogeneous mass insinuating around the conus medullaris and extending throughout the lumbar spine. The inferior component of the mass has signal characteristics similar to the CSF.
References
1. Esquenazi Y, Kerr K, Bhattacharjee MB, Tandon N. Traumatic rupture of an intracranial dermoid cyst: Case report and literature review. Surg Neurol Int. June 2013;4:80.
2. Zhang Y, Cheng JL, Zhang L, et al. Magnetic resonance imaging of ruptured spinal dermoid tumors with spread of fatty droplets in the central spinal canal and/or spinal subarachnoidal space. J Neuroimaging. January 2013;23(1):71–74.
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