Bilateral Primary Orbital Non Hodgkin’s Lymphoma Masquerading As Myositic Pseudotumor In An Elderly Patient

comprises 1-2% NHL and 8-10% extra nodal NHL. Orbital NHL commonly involves the superolateral quadrant and 20% are bilateral. An eighty year old patient presented with gradually increasing, bilateral proptosis, mild pain, congestion and chemosis for eight months. A firm rubbery mass was palpable in the inferior aspect of left orbit and superonasal aspect of right orbit. Visual acuity and extraocular movements were normal. Whole body work up was normal. CT orbits revealed a well defined solid mass lesion in the left orbit, extending from the infraorbital to retrobulbar region, encasing the inferior rectus and inferior oblique, with tendon involvement. The lesion had a similar echotexture to muscle, involving the intraconal and extraconal compartments. The fat plane between the lesion and muscle was obliterated. Based on confluence of clinical and radiological findings, myositic pseudotumor was strongly suspected. Incision biopsy showed extranodal aggregates of small lymphocytes with clumped chromatin and indistinct nucleoli. Immunohistochemistry confirmed low grade B cell NHL. Orbital lymphoma can closely mimic inflammatory pseudotumor clinically and radiologically. Both entities present with common clinical features like proptosis, periorbital swelling, chemosis, restriction of movements and visual complaints. On imaging, a minority of lymphoma can demonstrate features of pseudotumor by an atypical location in the orbit, dual compartmentalisation (intraconal and extraconal), echotexture resembling muscle, tendon involvement and fat infiltration. Biopsy and histopathological examination confirms the diagnosis in such masquerades. Abstract