Teaching Case

A 69-year-old man presented to the Ophthalmology Department of our hospital with right orbital swelling, bilateral painless diplopia and mild right proptosis for 11 months. He had no relevant medical history. Fundoscopy was normal and other ophthalmologic examinations did not demonstrate any additional findings.

Contrast-enhanced CT orbits show a homogeneous soft tissue mass located in the right superomedial orbital quadrant, causing mild proptosis (Figs 1a-b). This is composed of a small extraconal component extending towards the upper eyelid and an intraconal element involving the globe (Fig 1c). The lesion involves superior oblique and medial rectus muscles and has a wide plane of contact with the optic nerve suggesting perineural infiltration (Figs 1d-e).
On T1-weighted MR imaging the mass is slightly hypointense to extraocular muscles and mildly hyperintense on T2W (Figs 2a-b). After contrast administration it shows homogeneous enhancement (Fig 2c). High B1000 and low ADC values are demonstrated on DWI (Fig 3). Adjacent fat and lacrimal gland tissue appears normal. No associated osseous erosion. The contralateral orbit is normal.
Imaging findings were consistent with primary orbital lymphoma which was histologically proven via biopsy with a final diagnosis of orbital adnexal MALT lymphoma (OAML).

Primary lymphoma of the orbit is one of the most common orbital tumours and accounts for as much as half of all orbital malignancies [1, 2]. Lesions may be a manifestation of systemic lymphoma or arise primarily in the orbit. 5-15% of all extranodal lymphoma arises in ocular adnexa such as the conjunctiva, lacrimal gland, orbital fat, eyelid and lacrimal sac [1]. Non-Hodgkin lymphoma, specifically the OAML subtype, is the most common primary orbital lymphoma [1, 2]. Recently an association between chlamydia psittaci infection and OAML has been described [1, 3].
Patients typically present with exophthalmos, a palpable mass, proptosis, diplopia and a variable degree of impaired ocular motility [1]. Conjunctival involvement may lead to the finding of a swollen 'salmon red patch'. Pain is an uncommon symptom [1, 2].
The majority of lesions are unilateral and extraconal, most in the superolateral quadrant of the orbit [1]. On imaging examinations OAML may demonstrate diffuse infiltration of ocular adnexa with a tendency to involve orbital structures such as the globe and optic nerve, as in our case, although it can also appear as a smooth, circumscribed mass [2]. On non-contrast CT, it shows homogeneous attenuation, isodense or slightly hyperdense compared to extraocular muscles. MRI reveals an iso -or hyper-intense T2-weighted lesion, iso- or hypo-intense on T1-weighted images. Uniform, strong contrast enhancement on CT/MRI is characteristic [1, 2, 4]. Tumours have high B1000 signal on DWI and a low ADC value, similar to lymphoma in other locations [1, 5].
Differentiation of lymphoma from idiopathic orbital inflammatory pseudotumour is often challenging on imaging. Findings of infiltration or thickening of extra-ocular muscles favours a diagnosis of pseudotumour and high B1000 signal intensity on DWI with a low ADC value favours lymphoma [1, 2, 5]. Moreover, orbital pseudotumour displays no specific attenuation values on CT and its signal intensity on MRI depends on the degree of fibrosis [4]. In addition, the patient’s clinical history is often helpful, since patients with pseudotumour present with acute onset pain and those with lymphoma typically have no pain [1]. However, biopsy is ultimately required to establish the diagnosis [2, 3].
OAML has an excellent prognosis, with a 5-year overall survival rate of >90% [4]. Systemic dissemination occurs in 5–10% of cases [1, 3].
OAML has no preferred treatment: observation, resection, antibiotic therapy, radiotherapy, immunotherapy, chemotherapy have all been used [1, 3]. Our patient is currently receiving chemotherapy (Bendamustina-Rituximab).