Fig. 10.30. Pseudotumour of the orbit: fibrous tissue with necrotic fat cells is infiltrated by large groups of lymphocytes. Immuno-histochemistry is necessary to rule out a malignant lymphoma sive bony destruction of the orbital walls with associated orbital cellulitis. In patients with poorly controlled diabetes, but also in immunocompromised patients, orbital cellulitis can also be caused by fungal agents, for example mucormycosis. Presenting symptoms most frequently include oedema of the upper eyelid, headache and facial pain. Sometimes it can be asymptomatic. Clinically, orbital cellulitis is of great importance, as it is a severe disease with potentially disastrous consequences. Despite antifungal or antibacterial therapy, disease can progress. It may lead to optic neuritis, optic atrophy, blindness, cavernous sinus thrombosis, intra-cranial abscess formation, meningitis, subdural empy-ema, and even death. An incision biopsy of the process can be helpful in the diagnostic work-up. Histology will show an extensive neutrophilic infiltration of the orbital fibrous tissue and fat. The causative microorganisms can often be found with PAS, Gram and silver stainings. It is important for the pathologist to look for underlying causes, like tumours.
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