Department of Pathology, University of Oklahoma Health Sciences Center

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Answer: E (An arachnoid cyst.)  Level of difficulty: 1 NeuroTest NeuroLearn NeuroHelp

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  Arachnoid cyst Colloid cyst Enterogenous cyst

Rathke's cleft cyst

Dermoid cyst Epidermoid cyst
Incidence Common Uncommon Rare Uncommon Uncommon More common than dermoid cyst.
Etiology Multiple possible mechanisms including leptomeningitis, trauma, and malformation. Probably due to maldevelopment and most investigators favored a neuroepithelial origin. There are also evidence that favors endoderm origin. Probably due to maldevelopment.  Cystic enlargement of remnants of Rathke's pouch. Inclusion of ectodermal elements during closure of neural groove between the third and fifth weeks of embryonic life. Malformation of the adjacent structure can occur. Some of them may remain communicating with the overlying skin through a dermal sinus. Traumatic introduction of skin fragment is also a possible mechanism. Similar to dermoid cyst.
Location About half of the cases occurs along the Sylvian fissure, other common locations include the cerebellar pontine angle and quadrigerminal area, vermian area, sellar and suprasellar area.  Third ventricle. Spinal cord, most common in the cervical and upper thoracic segment. Less common in other spinal levels. Rarely seen as intracranial cyst. Pituitary. The smaller cyst are usually identified as a small cyst at the interface of the anterior and posterior pituitary; most of these small cysts are asymptomatic.  Most of them are intracranial and arise in the posterior fossa, usually along the midline in the vermis. About one-tenth of all cases are intraspinal and they are most commonly found in the lumbosacral region; they can be both intra- or extramedullary. Most of them are seen in the cerebellopontine angle and parapituitary area. Less than one-tenth of the cases occur in the spinal cord. Parapituitary tumors are usually embedded in the temporal bone. Similar to dermoid cyst, the pineal area is rarely involved.
Clinical May be clinically silent. Symptomatic cases have manifestations of a gradually expansile mass leading to increased intracranial pressure. May cause hydrocephalus, particular the cerebellar cysts. Clinical presentations are often seen in the third to fifth decades of life. The location of colloid cyst often makes it an effective block of foramen of Monro leading to acute hydrocephalus. Its pedunculated nature, however, allows change in position easily and release of the pressure built up. As a result, they are often associated with intermittent headache. Sudden death has been well documented. Smaller cysts may remain asymptomatic. Clinical manifestation is related to compression and disruption of spinal cord function.  Symptoms are due to compress of local structures and may lead to headache, hypopituitarism, hyperprolactinemia, visual disturbance and, rarely, diabetes insipidus.  Most of the spinal cases are discovered in the first and second decades of life; intracranial cases are seen in slightly older patients. Symptoms are usually due to local compression, irritation and to increased intracranial pressure due to hydrocephalus. Leakage of the kertinous content will lead to extensive granulomatous meningitis. They are found over a wide age range but most of them are discovered in the fourth to sixth decades. The clinical manifestations is due to local compression, irritation, and hydrocephalus. Leakage of the kertinous content will lead to extensive granulomatous meningitis.
Gross  The size is variable but some can attain a very large size. They are fluid filled cysts with thin, transparent wall. The cyst can be well distincted from the leptomeninges and dura. The fluid is usually clear and colorless.  The size varies form several millimeter to 3-4 cm. The cyst is round, unilocular and have a thin wall. After fixation, the cyst content appears as a gray hyaline substance with consistency of soft cartilage. Most of them are intra- or subdural, occasionally intramedullary. Well-defined, small, thin walled cyst with a watery to mucinous, occasionally xanthochromatic due to prior hemorrhage, content. Well-defined round to oval, opaque, "pearly" mass of variable size. The thickness of the wall is variable. The content is greasy material due to secretion of sebaceous glands. A variable amount of hair is present. Solid components may be present. The distinction between dermoid cyst and cystic teratoma is not entirely sharp. Well-defined round mass with a irregularly nodular capsule with a pearly discoloration.  
Histology Most of them have a thin, collgeneous cyst wall lined by stratified and compressed meningothelial (arachinoid) cell. The internal lining range from cuboidal, columnar, to ciliated. Mucin producing cells can be found in some cases. The cyst content is PAS(+). Rathke cleft cyst cannot be histologically differentiated from colloid cyst of the third ventricle. Clinical correlationis important.  The cyst wall is composed of connective tissue. The lining epithelium varies from low to high columnar cells that may have pseudostratification. Mucous secreting cells can be found.  Occasionally, they are ciliated. The cyst is lined by a single layer of cuboidal to columnar, ciliated or mucin-producing epithelium. Squamous metaplasia may occur and raises the possibility of a craniopharyngioima. Occasional cells of anterior pituitary gland may be present. Rathke cleft cyst cannot be histologically differentiated from colloid cyst of the third ventricle. Clinical correlationis important. The internal lining is very similar to skin and skin appendages are present. Leakage or escape of the content may lead to a wide spread granulomatous meningitis with foreign body giant cell reaction. The histology is similar to that of dermoid cyst except that no skin appendages are found. Rare cases of malignant transformation into invasive squamous cell carcinoma has been documented.