A true cyst is an enclosed space usually containing fluid and lined by epithelium. A pseudocyst is a cystlike structure without epithelial lining.
Cysts may be classified on the basis of their pathogenesis and histologic features. The primary categories are appendageal and adnexal cysts, developmental cysts, pseudocysts, and neoplasms with cystic changes. The most common lining is stratified squamous epithelium, which is observed in the most common appendageal cysts, such as the epidermoid (infundibular) and pilar (isthmic catagen, trichilemmal) cysts. Some developmental cysts have a lining of columnar epithelium and are classified as cutaneous columnar cysts; these cysts include branchial, thyroglossal, thymic, bronchogenic, cutaneous ciliated, and median raphe cysts. The term ciliated cyst has been used for several unrelated entities with a ciliated epithelial lining; these unrelated entities represent aberrant embryologic processes because no typical cutaneous structures contain cilia.
Columnar cysts are developmental cysts derived from embryologic vestiges, such as the branchial arch cleft, the thyroglossal duct, the tracheobronchial bud, the urogenital sinus, and müllerian structures. Some of these cysts arise along the lines of embryologic closure. Many midline cystic structures represent incomplete involution of the embryologic vestiges and are typically located in areas where these structures appear. Most of these lesions may appear anywhere in the course of these embryologic structures from the deep parts of the tissue up to the skin surface. They are clinically noticed if they cause recognizable subcutaneous masses, but they may remain unrecognized if they are deep and asymptomatic. All lesions may have cysts, fistulae, or sinuses in the same anatomical region.
Branchial cleft cysts (lateral neck cysts) are located in the anterior triangle of the neck, anterior of the sternocleidomastoid muscle. They originate from remnants of the second, third, and fourth cervical clefts. 
Thyroglossal cysts are the most common midline structures in the neck, occasionally visible at the base of the tongue. When the thyroid anlage descends from the base of the tongue to the anterior part of the neck, it remains connected to the base of the tongue by a midline embryonic structure, the thyroglossal duct. This duct disappears by the ninth week of gestation. If the duct or a part of it persists, a thyroglossal sinus, a cyst, or ectopic thyroid tissue may develop anywhere along the duct. [2, 3, 4, 5]
The thymus develops from the inferior part of the third pharyngeal pouch and migrates to the mediastinum. Parts may remain in the neck and the thyroid gland and may form an ectopic thymus; thymic cysts may develop from remnants of the thymopharyngeal duct. 
In male patients, median raphe cysts may be observed on the ventral aspect of the penis as subcutaneous cysts anywhere in the midline from the urethral meatus to the anus. Several hypotheses exist to explain median raphe cysts, including incomplete fusion of the urethral folds during embryonic development, ectopic periurethral glands of Littre, and anomalous outgrowth and sequestration of columnar epithelium from the urethra occurring after closure of the median raphe. [16, 17, 18, 19, 20, 21, 22, 23, 24]
Cutaneous ciliated cysts may occur anywhere but are primarily observed on the legs of female patients. They may represent migratory müllerian duct structures related to the fallopian tubes, the uterus, and the upper part of the vagina.  The occasional appearance of cutaneous ciliated cysts in males may be the result of vestigial müllerian structures, or the cysts may be the result of a different genesis (eg, derived from sweat glands). Female hormones may play a role in stimulating the ciliated epithelium. [26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37]
All developmental cysts are uncommon. The least common cyst is probably the cutaneous ciliated cyst, with fewer than 30 cases reported. The most common cyst is the thyroglossal cyst.
No racial predilection is known.
Cutaneous ciliated cysts are primarily observed in females. Median raphe cysts are primarily observed in males. The other cysts have an equal sex ratio.
All developmental cysts are present at birth and are enhanced by agents, such as hormones and trauma, to become clinically evident.
Thyroglossal cysts present in the first decade of life.
Thymic cysts present in the first or second decade of life.
Bronchogenic cysts and median raphe cysts present early, some at birth, while others present within the first 3 decades of life.
The cutaneous ciliated cyst usually presents in the second or third decade of life.
In general, the prognosis of patients with these cysts is favorable. Recurrence is infrequent provided that the excision was complete and that embryologic remnants were also removed. [38, 39] If a cyst develops a malignancy, the type of neoplasm determines the prognosis.
The cutaneous presentation of a cyst often represents only the superficial aspect of a deeper process. In areas of the head and the neck, deep extension may involve vital structures in the neck and the central nervous system. Lingual thyroglossal cysts may cause feeding problems and airway obstruction in neonates. Thyroglossal duct cysts may be inapparent until complications, such as inflammation, rupture, or infection, occur. Although rare, papillary thyroid carcinoma may develop in thyroglossal cysts during adulthood.  Squamous cell carcinoma in branchial cysts is another rare complication.