Lymphangiomas can be divided into three categories: cystic lymphangiomas or lymphadenomas, which contain large macroscopic lymphatic cystic spaces composed of collagen and smooth muscle; and cavernous lymphangiomas, which consist of buds that eventually form lymphatic vessels that develop with less space. Capillary lymphangioma, which consists of small lymphatic vessels, contains the smallest cystic space. Cystic lymphangiomas is the most common type of lymphangioma[6, 7]. There are many reference mechanisms that may explain the pathophysiology of lymphedema. For example, embryologically, during the normal development of lymphatic vessels, lesions associated with lymphedema are thought to originate from isolated lymph tissue in the lymphatic sac, which cannot communicate with the rest of the lymphatic or venous system. Subsequent expansion of isolated lymphoid tissue leads to cystic morphology of these lesions[8]. Therefore, this mechanism can explain why there is a high probability of lesions in children but an extremely low probability in adults.
Lymphocytic tumors can occur in adults. Clinical symptoms usually appear in the form of soft or hard nodular masses of an unclear nature on the extremities that cause pain when under pressure, during movement, or with trauma but rarely cause pain when a person is not moving[5]. Ultrasound can detect such cystic masses with high sensitivity and is an ideal initial imaging examination method for tumors of unknown nature. It is readily available, relatively inexpensive, and does not involve ionizing radiation. Therefore, it can be used as the primary examination. The disadvantage is that it is too extensive and less specific for lymphoma. Cystic lymphangioma can appear as a multilobular mass with internal septations and anechoic fluid during ultrasonography, and the identification of intra- or intra-cystic echogenic intervals is an important factor in diagnosis[9]. MRI is a necessary condition for the diagnosis of cystic lymphedema at present. Relying on its improved soft tissue resolution and ability to differentiate different tissue types, MRI provides a more accurate description of cystic masses. It not only can explain the invasion of surrounding tissue by a lesion, but also provide indispensable information for selecting the surgical range. On MRI, depending on the contents of the capsule, a lesion can be shown as serous, chylous, hemorrhagic, or mixed. However, in general, lymphangiomas are hypointense or isointense relative to muscle on T1WI and hyperintense on T2WI[10]. Histopathological examination is the “gold standard” for diagnosis of lymphoma and can be accurately diagnosed. H&E staining can show dilated cystic spaces lined with flat endothelium and a cyst wall rich in lymphocytes, smooth muscle, and irregular small fatty cysts. However, H&E staining is sometimes difficult for diagnosis of lymphoid tissue. IHC staining of cystic lymphangioma with monoclonal antibody D2-40 is more sensitive than H&E staining, which can improve accuracy. D2-40 is a specific lymphatic endothelial marker[11], which specifically stains lymphatic vessels and does not react with vascular endothelial cells[12]. At present, if the disease affects the body's function or appearance, the ideal treatment is radical resection to reduce recurrence. Incomplete resection is the only cause of relapsed disease[13], and the probability of recurrence ranges from 0–13.6%[14].
In conclusion, lymphoma is common in children and rarely occurs in the forearms of adults. Clinical and imaging evaluations are necessary, but the final diagnosis is likely to be made by pathological evaluation of a resected specimen. Although complete resection of lymphangiomas can be a major challenge and may be associated with serious complications, lymphadenomas rarely resolve spontaneously, especially if they are symptomatic, and cause human physiological dysfunction. Radical resection is the main treatment. Regular follow-up is required after surgery to monitor a cyst for recurrence.