extranodal involvement is seen in approximately 25% cases of nonhodgkin 's lymphoma ( nhl ) . primary adrenal lymphoma ( pal ) is rare with fewer than 200 cases reported in english literature . the majority of the patients with pal present with bilateral adrenal masses and diffuse large b - cell ( dlbcl ) type is the most common type on histology . unilateral presentation and t - cell / natural killer ( t / nk ) cell histological type is rarer . due to the rarity of the disease , there is a paucity of literature on the role of fluorine-18 fluorodeoxyglucose positron emission tomography / computed tomography ( f-18 fdg pet / ct ) scan in pal . we report f-18 fdg pet / ct scan findings in a case of unilateral t / nk cell pal performed for staging and interim treatment response assessment . a 41-year - old gentleman with no co - morbidities presented with the progressive left hypochondriac pain of 1-month duration . ct guided biopsy with immunohistochemistry revealed tumor cells positive for leukocyte common antigen , cd3 , and weakly positive for cd56 ; while negative for cd20 , cd4 , and cd8 suggestive of high - grade nhl of t / nk cell immunophenotype [ figure 1 ] . staging f-18 fdg pet - ct scan revealed increased metabolic activity in the left adrenal mass . no focus of hypermetabolism was noted elsewhere in the body suggestive of stage i aex ( left adrenal ) [ figure 2 ] . ( methotrexate , dexamethasone , leucovorin , ifosfamide , etoposide , and l - asparaginase ) chemotherapy regimen . interim fdg pet - ct for response assessment post four cycles of chemotherapy revealed complete metabolic and morphological regression of the primary left adrenal mass . biopsy of the left adrenal mass : ( a and b ) photomicrographs showing features of nonhodgkin 's lymphoma with diffuse architecture composed of intermediate to large atypical lymphoid cells ( h and e , 4 and 40 respectively ) . ( h ) cd-8 ( 40 ) increased fluorodeoxyglucose uptake was noted in the left suprarenal gland on maximum intensity projected : ( a ) . ( c ) images of the staging positron emission tomography / computed tomography scan in case of biopsy proven adrenal lymphoma . positron emission tomography / computed tomography scan done post four cycles of  smile  chemotherapy regimen revealed complete metabolic and morphological response ( d - f ) pal is defined as the presence of adrenal lymphoma without any evidence of nodal involvement or leukemia . although secondary adrenal involvement in nhl is seen in approximately 25% of cases , pal is rare comprising < 1% of nhl and 3% of extranodal nhl with < 200 cases reported in english literature . most of the patients present with nonspecific symptoms such as abdominal pain , fever , and weight loss . in 60% cases , advanced age at diagnosis , large tumor size , increased ldh level , bilateral adrenal involvement ( regarded as stage iv disease ) , and adrenal insufficiency at the time of presentation are poor prognostic factors . since adrenal gland is devoid of lymphoid or hematopoietic tissue , pal is believed to originate from differentiation of primitive totipotent mesenchymal cells . , none of these theories has been conclusively proven due to the rarity of the disease . there are only 5 - 6 cases of t / nk - cell type pal reported in the literature so far , most of them with bilateral adrenal involvement . conventionally , ct scan is used as a first imaging modality for characterization of adrenal lesions . t2-weighted magnetic resonance imaging with chemical shift sequences is also often used to differentiate benign from malignant adrenal masses . f-18 fdg pet / ct scan has an established role in staging , restaging , interim response assessment , and prognostication of lymphomas . various studies have shown higher accuracy of f-18 fdg pet / ct scan in differentiating malignant and benign adrenal masses . yun et al . have shown that fdg pet has a 100% sensitivity , 94% specificity , and 96% accuracy for characterization of adrenal lesions . however due to the rarity of the disease , there is a paucity of literature on the role of fdg pet / ct scan in pal . in our case , baseline fdg pet / ct showed intense uptake in the left adrenal mass with no other nodal or extranodal disease detected elsewhere in the body . hence , in correlation with the biopsy findings , whole body fdg pet / ct played a paramount role in differentiating primary versus secondary involvement of adrenal gland . a study by khong et al . assessing the role of mid - treatment fdg pet / ct for early response assessment of smile therapy in nk / t - cell lymphoma demonstrated that deauville score on mid and end treatment fdg pet / ct is the only significant independent predictor of both overall survival and progression free survival . to the best of our knowledge , this is the first case reported in the literature where a complete metabolic and morphological response was seen on interim fdg pet / ct in a case of unilateral pal of t / nk - cell type treated with smile regimen . therefore , our case further reinforces the valuable role of fdg pet / ct for diagnosis , staging , and treatment response evaluation in pal .