rosai - dorfman disease ( rdd ) , also known as sinus histiocytosis with massive lymphadenopathy most often presents as a painless , massive bilateral enlargement of the cervical lymph nodes associated with fever , leucocytosis , elevated erythrocyte sedimentation rate ( esr ) , and polyclonal hypergammaglobulenemia . it is characterized by marked lymphoplasmacytic and hystiocytic infiltration with emperipolesis ( lymphophagocytosis ) in the lymph nodes . although extranodal rdd ( involving the orbit , upper respiratory tract , skin , subcutaneous tissue , skeletal system , central nervous system , etc . ) is found in 40% of the patients with rdd , involvement of the thyroid has been reported rarely . so far , six cases of rdd involving the thyroid were reported in literature , all occurred in females with a mean age of 56.3 years . all the cases were initially diagnosed as thyroid malignancies with lymph nodal metastasis , both clinicoradiologically and cytologically.[24 ] the cytological features of rdd involving the thyroid are virtually diagnostic and can obviate the need for a biopsy in most cases . a 15-year - old female presented with multiple , painless enlargement of the cervical and submandibular lymph nodes along with thyromegaly and fever since three months . she was initially diagnosed outside as having tuberculosis and was under antituberculous treatment since two months , to which there was no response . routine laboratory investigations revealed hemoglobin of 10 gm% , erythrocyte sedimentation rate of 90 mm at the end of first hour , total leukocyte count of 14,600 cells / mm and a differential count of neutrophils-44% , lymphocytes-52% , monocytes-2% , eosinophils-2% . fine needle aspiration cytology ( fnac ) was performed from the thyroid as well as the lymph nodes . smears were stained with giemsa as well as hematoxylin and eosin and found to be richly cellular [ figure 1 ] . smears from both the lesions , that is , thyroid and lymph nodes showed a similar cytomorphological picture . microscopic examination revealed the presence of histiocytes with single to multiple nuclei , fine nuclear chromatin and inconspicuous - to - prominent nucleoli ; no nuclear grooving or atypia was noted . the histiocytes had abundant pale cytoplasm containing numerous intact lymphocytes ( emperipolesis ) [ figure 1 lower inset ] , plasma cells and neutrophils [ figure 1 upper inset ] . based on this characteristic cytomorphology , a diagnosis of rosai - dorfman disease , nodal and extranodal , involving the thyroid , was made , ruling out malignancy . the patient was treated with steroids with a good response and thus an unnecessary total thyroidectomy was prevented . cellular smears with clusters of histiocytes over a lymphocytic background ( h and e , 100 ) . upper inset shows histiocytes with emperipolesis of neutrophils ( h and e , 400 ) and lower inset shows emperipolesis of lymphocytes ( giemsa , 1000 ) rosai - dorfman disease is a rare histiocytic disorder of unknown etiology involving the lymph nodes . extranodal rdd involving the thyroid is still rare . so far , in the literature six cases of rdd involving the thyroid have been reported . although most cases of nodal rdd occur during the first or second decade of life , with a male predominance , all the previously reported six cases of rdd involving the thyroid have occurred in elderly females with a mean age of 56.3 years . the clinical presentation of rdd as described in the initial publications consists of painless , bilateral cervical lymphadenopathy associated with fever , leucocytosis , elevated esr , and hypergammaglobulenemia . a wide range of extranodal involvement described recently includes involvement of the eyes , respiratory tract , including nose , skin , subcutaneous tissue , bone , skeletal muscle , central nervous system , intestinal tract , salivary glands , genitourinary tract , thyroid , breast , liver , kidney , heart , uterine cervix and so on . our case was a 15-year - old female , who presented with multiple cervical and submandibular lymphadenopathies , diffuse thyromegaly , fever , leucocytosis and elevated esr . however , the possibility of rdd involving thyroid was not considered until fnac was performed . the cytological features of rdd usually reveal numerous large histiocytes with abundant pale cytoplasm and ingested lymphocytes ( emperipolesis ) . the histiocytes show positive immunostaining for s100 protein , cd14 , cd11c , cd33 and cd68 antigens in the cytological smears . differential diagnosis of rdd involving the thyroid include undifferentiated carcinoma , langerhans cell histiocytosis , thyroiditis and lymphoma . in undifferentiated thyroid carcinoma , the neoplastic cells show highly pleomorphic and hyperchromatic nuclei and neoplastic spindle cells . in the langerhans cell histiocytosis , de quervain thyroiditis should be differentiated from rdd on the basis of the presence of multinucleate giant cells , degenerating thyrocytes , inflammatory cells , macrophages , colloid and dirty background and absence of emperipolesis and lymphadenopathy . in hodgkin lymphoma , the smears show lymphocytes , plasma cells , histiocytes , eosinophils and the characteristic reed  sternberg ( r - s ) cells . in rdd , rdd involving the thyroid , although rare , can be diagnosed by the characteristic cytological features , obviating the need for a biopsy . ours is the first case of rdd involving the thyroid to be diagnosed by fnac , to the best of our knowledge .
rosai - dorfman disease ( rdd ) , also known as sinus histiocytosis with massive lymphadenopathy is a rare disease involving the lymph nodes . 
 extranodal rdd involving the thyroid is extremely rare . 
 so far , six cases of rdd involving thyroid have been reported in the literature ; all have occurred in females with a mean age of 56.3 years . 
 clinically , radiologically and cytologically , all the cases were initially diagnosed as thyroid malignancies with lymph nodal metastasis . 
 the final diagnosis was made histologically only after total thyroidectomy . 
 we herein , present a seventh case of rdd involving the thyroid in a 15-year - old female , diagnosed first on fine needle aspiration cytology ( fnac ) . 
 we conclude that fnac is a useful diagnostic procedure for rdd involving thyroid ; it can avoid an unnecessary thyroidectomy .