PET-scan in orbital Malt lymphoma and its value in diagnosis and management: a series of four cases

The orbital location of mucosa associated lymphoid tissue (Malt) lymphoma (ML) is rare and can appear in very different forms. Biopsy is decisive for diagnosis. Although the positron emission tomography (PET) scan is rarely used in ophthalmology, it appears useful in our experience. We report four cases illustrating the diversity of the orbital localization in ML. Case 1 is a 41-year-old woman presenting unilateral corticosteroid-resistant dacryoadenitis. The PET-scan clearly fixed at the orbit. After anatomopathologic confirmation, a 36-Gy orbital radiotherapy was carried out, leading to the clinical and tomographic remission. Case 2 is a 61-year-old patient, presenting a small cell carcinoma of the lung, initially referred for unilateral exophthalmia. MRI highlighted a bilateral orbital infiltration, with a hot spot on the PET-scan. The clinical suspicion of orbital metastasis was not confirmed: the biopsy concluded in ML. Case 3 is a 64-year-old woman, referred for unilateral and resistant conjunctival hyperemia. Clinical diagnosis was myositis of the superior rectus muscle. The PET-scan did not fix in the orbit but revealed a pleural location. The muscular biopsy concluded once again in ML. Case 4 is a 68-year-old woman who had a history of sinusal ML. Diplopia with a second orbital location, non specific in CT but fixed in PET, was found. The biopsy concluded in ML with transformation toward an aggressive lymphoma. Although the lacrimal gland location is well-known, unspecific orbital infiltration and orbital myositis are less common, which highlights the value of a non invasive exploration before biopsy. The advantages of the PET scan in orbital ML has not been sufficiently studied. In our experience, it was useful in these four cases. Orbital ML can take on different aspects that are sometimes misleading. PET is very useful in diagnosis before the biopsy, in therapeutic decisions, and in follow-up after treatment even if it does not always fix in the orbit.