Sequestration dermoid

Sequestration dermoid cyst

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Sequestration dermoid cyst

This is a congenital variety of dermoid cyst, which is formed by the inclusion of epithelium buried at the line of embryonic fusions. So these are found along the lines of fusion of the two embryonic segments.

This cyst is lined by stratified squamous epithelium with hair, hair follicles, sebaceous glands, and sweat glands. It contains white pultaceous, tooth paste like desquamated material with or without hair. It is the mixture of sebum, sweat, and desquamated epithelial cells.

The common sites are over the external angular process of the frontal bone (the external angular dermoid at the upper outer margin of the orbit), the root of the nose (internal angular dermoid) and in the midline. When in relation to the skull, the underlying bone is usually hollowed out around it. The possibility of communication with an intracranial dermoid or the meninges should be excluded by skull radiography or computed tomography (CT) scan prior to excision

Origin

At the line of embryonic fusion, a few ectodermal cells are sequestrated into the deeper layer. Ultimately these cells proliferate and liquefy to form a sequestration dermoid cyst. Such cyst lies almost near the mesoderm from where the bones develop, that is why indentation is often found in the underlying bone. Sometimes the cyst starts in the mesoderm so that there may be prolongation of the cyst through the bone and a portion of the cyst may remain intracranial.

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Clinical Features

The cyst may be noticed at birth, but it is usually seen a few years later-the time taken to form the cyst.

A painless swelling, which is slowly growing is the main symptom. Cosmetic disfigurement is the main complaint. Such cyst hardly becomes big enough to cause any serious mechanical disability and rarely may become infected.

Such cysts hardly attain a size bigger than 2 cm in diameter. They are usually ovoid or spherical in shape and have a smooth surface and do not have punctum which is often found in sebaceous cysts.

The cyst feels soft and indents with pressure as the content is thick pultaceous material, a mixture of sebum, sweat, and desquamated epithelial cells.

The skin can be lifted off the cyst easily. This cyst is also free from underlying structures. There may be bony indentation when the bone lies exactly deep to the cyst.

Treatment

Complete excision of the cyst is the treatment of choice. This should be done under general anesthesia as the cyst has to be dissected from the sensitive pericranium; moreover, there may be an intracranial extension.

If preliminary X-ray shows a gap in the underlying bone, the operation has to be delayed to give an opportunity for spontaneous closure.

If there is an intracranial extension, osteoplastic flap should be removed for excision of the intracranial part.

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