Insufficient development during embryo-fetal life of anatomic structures in charge of lymphatic drainage, which, therefore, are hypoplastic and often insufficient to cope with normal lymphatic drainage. There are different degrees of lymphatic hypoplasia: in the most severe cases, lymphatic insufficiency becomes clinically overt after a few days from birth, whereas in patients with moderate deficit, it may become clinically overt even after many years, or develop concurrently with traumatic or surgical lesions that damage the lymphatic structures.