The patient is an 64 year old white male who presented with left sided back pain. Imaging showed a left perinephric retroperitoneal hematoma and a left renal lower pole cystic lesion with hemorrhage. Additional imaging showed numerous pulmonary lesions. A An endobronchial ultrasound guided fine needle aspiration was scheduled.

The concern is a primary renal malignancy with metastatic disease to lungs. An endobronchial ultrasound guided FNA is scheduled. An onsite rapid diagnosis by cytology was scheduled.

CytologicallyYoursCoW20131209Cytology1.jpg|4x magnification of a 4R lymph node. There Groups of cohesive epithelial appearing cells can be seen on low power. Lymphoid tissue is a polymorphic lymphoid population with scattered large atypical cellsnot easily identified.CytologicallyYoursCoW20131209Cytology2.jpg|20x magnification of paracaval a 4R lymph node. There This is a cellular specimen with groups of cells along what appear to be a papillary or papillary-like structure. Single cells are small lymphocytes with also dispersed in the background lymphoglandular bodies. Scattered eosinophils and large atypical The cells with prominent nucleoliare haphazardly arranged.CytologicallyYoursCoW20131209Cytology3.jpg|40x magnification of paracaval a 4R lymph node. There are On higher power, the nuclei appear mildly atypical binucleated cells among and the large atypical cellscytoplasm is delicate and finely vacuolated. The nuclear contours are somewhat irregular.CytologicallyYoursCoW20131209Cytology4.jpg|40x magnification Cell block of paracaval 4R lymph node. There The cytoplasm does not appear as vacuolated on alcohol fixed cell block material, but the nuclei are relatively uniform, but somewhat atypical binucleated cells among the large atypical cells. </gallery> ===Immunohistochemistry===<gallery heights="250px" widths="250px">CytologicallyYoursCoW20131209Cytology5.jpg|40x magnification of paracaval PAX8 on 4R lymph node. There are atypical binucleated cells among the large atypical cellsshows positive nuclear staining.

* <spoiler text="What is your differential diagnosis?">These groups of cells demonstrate malignant appearing cells in a background of an otherwise benign appearing lymphoid background. The atypical cells are scattered, with large nucleoli and several binucleate forms. In addition, there seem to other immunohistochemical stains that would be an increased number of eosinophils applicable in the background. The differential diagnosis includes Hodgkin lymphoma; however, the possibility of the large atypical cells being melanoma cannot be ruled out. </spoilerthis case?">* <spoiler text="What ancillary tests would you recommend?">For this patient, we recommended that the radiologist perform a biopsy of the lesion so that it could be sent for immunohistochemical workup. Since the overall percentage of the atypical cells were low, we were worried that a cell block would not contain enough of the malignant cells for additional stains. We also sent the lymph node for flow since a hematologic malignancy was suspected; however, with Hodgkin lymphoma, we don't expect any diagnostic findings from flow cytometry.</spoiler>RCC*CD10*PAX2* <spoiler text="What immunohistochemical stains would you do?">CD15, CD30, and PAX5 would stain tumor cells in Hodkin lymphoma. Mart1, HMB45, and S100 could be used to rule out melanoma. Other additional stain in a lymphoma versus melanoma workup might include CD3, CD20, and keratin.Kidney specific antigen</spoiler>

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* '''Positive for malignancy, the differential Rapid diagnosis includes melanoma and Hodgkin lymphoma''': Non-small cell carcinoma.* Final diagnosis: Renal cell carcinoma.