Lymphangiomas and cystic hygromas are rare benign hamartomatous lesions of the lymphatic system. Determining the true incidence of these lesions is difficult because uniformity in classification and nomenclature is lacking. Moreover, lymphatic malformations are generally treated in tertiary and quaternary medical centers, distorting any view of their true incidence. 
These lesions, more correctly referred to as lymphatic malformations, have a marked predilection for the head and neck, with as many as 75% presenting in the oral cavity.  No clear sex predilection is demonstrated, and whites appear to be affected more often than people of other races.
Of lymphatic malformations, 50% are present at birth, and 90% are diagnosed by the time the individual is aged 2 years. However, the time of diagnosis can range from 19 weeks' gestation to the individual's second decade of life.
Of lymphatic malformations in the oral cavity, 40-50% involve the dorsum of the tongue, which is the preferred site of intraoral involvement, and they range in size from 1-2 cm. [3, 4] Other sites of involvement include lips, buccal mucosa, soft palate, and floor of the mouth.  These distinctions can be somewhat artificial because lesions that involve the oral cavity may extend from the orbits to the upper mediastinum and axillae.
Lymphatic malformations are typically classified as simple microcystic (cavities smaller than about 2 cm3), simple macrocystic (cavities larger than about 2 cm3), or mixed microcystic and macrocystic lesions, according to their predominant histologic features. 
Although no clear consensus on the mechanism for lesion development exists, the lesions likely develop as a result of aberrant sequestration of portions of the primitive embryonic anlagen. The sequestered areas never achieve efficient anastomoses with the larger lymph channels and, as a result, they consist of little more than functionally blocked lymphatic tracts. This blockage may result in increased hydrostatic pressure with subsequent expansion of the lesion until a pressure equilibrium is achieved with the surrounding tissues. The importance of the surrounding tissues in determining the nature of the lesion is evident, as microcystic lesions are more common in the tongue, whereas macrocystic lesions predominate in the relatively compliant tissues of the neck.
At the molecular level, some have hypothesized overexpression of growth factors or their associated receptors essential to lymphatic development. Two examples would be vascular endothelial growth factor types 3 and C.
A neoplasm is classically defined as an abnormal mass of tissue. Its growth exceeds and is uncoordinated with that of healthy tissues and persists in an excessive manner after the inciting stimuli is removed. In contrast, lymphatic malformations and/or lymphangiomas tend to grow commensurately with the child's growth and rarely regress spontaneously. Rapid enlargement of the lesions (out of proportion with the surrounding tissues) is observed only in conjunction with infections of the upper respiratory tract or the lesion itself or with trauma and hemorrhage into the malformation. In addition, the lesions have a typical endothelial cell cycle.
For these reasons, lymphangiomas are considered to be malformations rather than neoplasms. In a teleologic sense, this determination remains rather unsatisfying because the predisposing event (ie, the sequestration of embryonic anlagen) occurs long before these lesions develop. As previously stated, only 50% of the lesions are diagnosed at birth, and a few reports of lesions developing in early adulthood exist.
Moreover, at prenatal ultrasonography, fetal lymphatic malformations are observed to develop and occasionally resolve in utero. Some unrecognized event must be superimposed on these earlier events resulting in the development of a clinically apparent lesion. These events are apparently reversible because the lesions occasionally spontaneously regress in fetuses and children. The inciting event must then be occurring during the maturation of the formed lymphatic systems.
Determining the true incidence of these lesions is difficult because uniformity in classification and nomenclature is lacking. Moreover, lymphatic malformations are generally treated in tertiary and quaternary medical centers.
The oral cavity is a highly specialized structure that is important for speech, deglutition, mastication, and airway maintenance. The functional and anatomic aberrations that result from an oral lymphatic malformation may negatively affect each of these specialized functions. In addition, the aesthetic consequences of an oral lymphatic malformation can be severe and significantly impair a child's psychosocial development. See Complications.
Approximately 70-80% of patients with lymphatic malformations experience infections, often associated with significant increases in the size of lesions.  Infection of oral lymphangiomas have also been complicated by overlying erysipelas, a skin infection.  Management of these episodes requires aggressive, early institution of broad-spectrum antibiotic therapy. This typically consists of admission to hospital for a course of parenteral antibiotics followed by a prolonged course of oral antibiotics. Susceptibility to infection of these lesions probably pertains to the structural abnormalities of the tissues and the lymphatic system and its important role in mounting an immune response. Further, lymphocytopenias have been documented in this population, although they have yet to be definitely correlated to an increased risk of infection. 
Rapid enlargement of the lesion either as a result of intralesional hemorrhage or infection may lead to airway obstruction. The clinician must be very vigilant in this regard. As a result of these concerns, approximately 50% of children with such lesions require tracheostomy.
Whites appear to be affected more than people of other races. One exceptional form of lymphatic malformation occurs on the alveolar ridge in approximately 4% of black neonates. This lesion, generally bilateral and small, resolves spontaneously and does not require treatment. 
No clear sex predilection is demonstrated; however, small lymphangiomas (< 1 cm) occurring at the alveolar ridge of the mandible do show a 2:1 male-to-female ratio. 
Of lymphatic malformations, 50% are present at birth, and 90% are diagnosed by the time the individual is aged 2 years. However, the time of diagnosis can range from 19 weeks' gestation to the individual's second decade of life. 
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