Re: Oral Lymphangiomas

[drmittal]

Pathophysiology
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.