Why the embryonic lymph sacs remain disconnected from the rest of the lymphatic system is also not known.Cystic lymphangioma that emerges during the first two trimesters of pregnancy is associated with genetic disorders such as Noonan syndrome and trisomies 13, 18, and 21. Chromosomal aneuploidy such as Turner syndrome or Down syndrome were found in 40% of patients with cystic hygroma. Pathophysiology
In 1976, Whimster studied the pathogenesis of lymphangioma circumscriptum, finding lymphatic cisterns in the deep subcutaneous plane are separated from the normal network of lymph vessels. They communicate with the superficial lymph vesicles through vertical, dilated lymph channels. Whimster theorized the cisterns might come from a primitive lymph sac that failed to connect with the rest of the lymphatic system during embryonic development.A thick coat of muscle fibers that cause rhythmic contractions line the sequestered primitive sacs. Rhythmic contractions increase the intramural pressure, causing dilated channels to come from the walls of the cisterns toward the skin. He suggested that the vesicles seen in lymphangioma circumscriptum are outpouchings of these dilated projecting vessels. Lymphatic and radiographic studies support Whimsters observations. Such studies reveal that big cisterns extend deeply into the skin and beyond the clinical lesions. Lymphangiomas that are deep in the dermis show no evidence of communication with the regular lymphatics. The cause for the failure of lymph sacs to connect with the lymphatic system is not known.Microscopically, the vesicles in lymphangioma circumscriptum are greatly dilated lymph channels that cause the papillary dermis to expand. They may be associated with acanthosis and hyperkeratosis.
Yao syndrome (YAOS) (formerly called NOD2-associated autoinflammatory disease) is an autoinflammatory syndrome involving episodes of fever and abnormal inflammation affecting many parts of the body, particularly the skin, joints, and gastrointestinal system. Signs and symptoms
Arthralgia (Arthritis)
Fever
Diarrhea
Abdominal Pain
Keratoconjunctivitis Sicca (Dry eyes)
Pleurisy
Idiopathic Pericarditis
Xerostomia (Dry mouth)
Erythematous Plaques
Dermatitis

Diagnostic criteria
Yao syndrome is diagnosed if 2 major criteria, at least one minor criterion, the molecular criterion, and exclusion criteria are fulfilled. Treatment
A study to determine the effectiveness of Novartis pharmaceutical drug Canakinumab was conducted. In this study, canakinumab was effective in patients with YAOS, and thus clinical trial of canakinumab may be warranted as a therapeutic option for this disease. Inheritance
Yao Syndrome inheritance is classified as Multifactorial Inheritance. References
External links

MedGen-Yao Syndrome
Genetics Home Reference-Yao Syndrome