Heterotopic Brain Tissue Encephalocele

Rathke's cleft cysts (or Rathke's cyst; named after Martin Heinrich Rathke, 1793-1860) arise from the Rathke's pouch (or hypophyseal duct), an ectodermal remnant of the stomodeum that gives rise to the anterior lobe of the pituitary gland. The Rathke's pouch is normally obliterated to become microscopic clefts, but remnants of the Rathke's pouch are incidental findings in up to 33% of un-selected autopsies. Rathke's cleft cysts can have diameters ranging from 0.3 to 4 cm [90, 192]. The thin-walled cysts are lined with respiratory epithelium with interspersed goblet cells and are filled with a clear, colloid, mucinous, viscous, turbid or haemorrhagic fluid. In cases of inflammation, metaplastic non-keratinising squamous epithelium and a mural lymphocytic infiltrate dominate [72, 90]. Rupture induces a granulomatous and xanthomatous inflammation with fibrosis, cholesterol needles and foreign body cell reaction, and even amyloid deposition. Rathke's cleft cysts are virtually never removed intact and surgical specimens typically consist of inflamed fibrous tissue. The epithelium is often elusive. Rare examples of Rathke's cleft cysts contain mural nodules of anterior pituitary tissue or concomitant pituitary adenoma. Most nasopha-ryngeal pituitary adenomas represent nasopharyngeal extension of intracranial pituitary adenomas. Primary nasopharyngeal pituitary adenomas are extremely rare and mostly non-functioning [110, 123]. Symptoms depend on the type of secreted hormone and the location of the adenoma. Histologically, ectopic pituitary gland tissue can display the entire spectrum with chromophobe, acidophilic and basophilic cells [29].

Encephaloceles are herniations of brain through a congenital opening of the skull. Glial heterotopias with and without encephaloceles cause neonatal airway obstruction and rhinorrhoea. Heterotopic brain in a nasopha-ryngeal location is rare [168]. From a pathologist's perspective, encephaloceles and brain heterotopias can be distinguished only after correlation with the patient's clinical and radiological findings. Histologically, mature neuroglial tissues are embedded in fibrovascular stroma. Encephaloceles/glial heterotopias involving the nasopharynx differ from the more common nasal gliomas in that they contain ependyma, choroid plexus, retinal components and occasionally neoplastic tissue, such as an oligodendroglioma [14].

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