A 60-year-old male with complaints of painless left-sided proptosis for three years. The visual acuity was 20/200 on right and 20/50 on left. No systemic complaints. On examination, a non-tender, non-pulsatile mass was palpated in superotemporal region of left orbit displacing the eyeball inferomedially. No change in size on Valsalva manoeuvre. Systemic examination was unremarkable. No evidence of organomegaly or lymphadenopathy. Routine blood investigations were within normal limits.
MRI examination of the orbit revealed a well circumscribed mass lesion in the superolateral aspect of left extraconal space showing indistinct fat planes with the lacrimal gland. The lesion measured 2.9(anteroposterior) x 1.7(transverse) x 2.5(craniocaudal) cm and appeared homogeneously isointense (to the extraocular muscles) on T1 and mildly hyperintense on T2 weighted images with few serpentine flow voids within. The lesion showed homogeneous enhancement on post contrast scan. Diffusion weighted images (DWI) showed diffusion restriction with a mean apparent diffusion coefficient (ADC) value of 0.67 x 10-3mm2/s (Fig. 1). MRI Screening of brain was performed which was unremarkable.
In view of patient’s age, history, location and morphology of the lesion, a provisional diagnosis of orbital lymphoma was suggested. However, on biopsy the lesion was found to be a mixed cell variant of extranodal Castleman’s disease.
No systemic involvement was observed on ultrasound of the neck and CT of the chest, abdomen and pelvis.
Castleman's disease, also known as angiofollicular lymphoid hyperplasia was first described by Dr. Benjamin Castleman in 1956. It is a non-neoplastic lymphoproliferative disorder of uncertain etiology with the possible role of Human herpes virus 8 in its etiopathogenesis. The disease has been classified into two clinical entities (unicentric and multicentric form) and three pathological types (hyaline-vascular, plasma cell and mixed cell type). It is a great mimic of both benign and malignant abnormalities in the neck, chest, abdomen, and pelvis . Extranodal involvement such as the orbit though extremely rare, has been reported. Hence, it should be considered as a differential in cases of suspected idiopathic orbital inflammation and lymphoproliferative disorders .
Ferreiro et al in their description of two cases of orbital Castleman’s disease reported intermediate signal intensity of the lesion on T1 and low signal intensity on T2 weighted images with significant restriction of diffusion on DWI . Kurokawa et al described the localisation of the lesion to the superolateral extraconal compartment or the lacrimal fossa as in our case . Bonekamp et al suggested the presence of prominent feeding vessels within the lesion or in its close vicinity as a clue to diagnosis, predominantly seen in hyaline vascular Castleman’s disease . Elkhamary et al reported the role of DWI in differentiating lymphoma from non-neoplastic lymphoproliferative conditions of the orbit and suggested that the mean ADC value of lymphoma was significantly lower than benign lymphoproliferative conditions owing to the hypercellular nature of the former .
The mass was excised via lateral orbitotomy. Patient’s symptoms resolved after surgery and no recurrence was noted in the one year follow up.
Histopathological examination revealed sheets of mature lymphoid tissue with pseudofollicle formation and interfollicular hyalinized blood vessels. Focal eccentric layering of the mantle zone (onion skinning) was present. On immunohistochemistry, an intermixed population of CD5 and CD20 with CD138 positive plasma cells was noted. Polyclonal expression of both kappa and lambda was seen. These findings were consistent with extranodal Castleman’s disease of mixed-cell variant.
Unicentric Castleman’s disease has favourable prognosis with surgery being curative (as in our case) while the multicentric variant requires systemic corticosteroids, chemo/immunotherapy and usually has a poorer prognosis.2
Orbital involvement in Castleman’s disease is uncommon. It must be considered in the differential diagnosis of a lesion in the superolateral extraconal orbit in the appropriate clinical setting. Systemic involvement must always be ruled out due to difference in the management strategy. Its close resemblance to lymphoma in its presentation, location and imaging findings often pose a challenge in differentiating the two entities and histopathological confirmation of diagnosis is needed.
Written informed patient consent for publication has been obtained.
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