Observation of lymphatic vessels in orbital fat of patients with inflammatory conditions: a form fruste of lymphangiogenesis?

In the absence of antibodies specific for lymphatic vessels, analysis of lymphatic vessels within different tissues has been widely performed with light microscopic and, most importantly, electron microscopic techniques. In regard to lymphatic vessels in the ocular globe and the periocular structures, controversy remains about the specific distribution of lymphatic channels. It is postulated that bulbar and retrobulbar tissues are devoid of lymphatic vessels, but lymphatic vessels have been demonstrated in lacrimal gland and epibulbar conjunctiva. In this study, we analyzed orbital fat for the presence of lymphatic tissue using D2-40, a monoclonal antibody, specific for lymphatic vessels. We found lymphatic vessels present within bulbar conjunctiva extending to the level of the ciliary apparatus. No lymphatics were identified in healthy anterior orbital adipose tissue. In two cases of orbital mucor-mycosis and one case of panendophthalmitis, significant lymphovascular proliferation was present within granulation tissue associated with the acute inflammation. We conclude that lymph vessel proliferation may be induced in inflammatory conditions in tissues which are normally devoid of lymph channels.