case_images: PMC6652101_01
case_images: MRI abdomen coronal and transverse images depicting renal lesion in middle and lower pole of the left kidney.
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case_images: After two weeks, the patient underwent MRI in which the hematoma had decreased in size to 5 cm, but the underlying cause could not be ascertained ( Figure 1).
case_images: Robotic assisted laparoscopic left partial nephrectomy with guidance of intra-operative ultrasonography.. (
  A) Intraoperative image during partial nephrectomy of the left kidney; (
  B) gross morphology of the resected tumour.
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case_images: Keeping in mind that a renal tumour, either benign or malignant, could be the cause of haemorrhage, the patient underwent robotic assisted laparoscopic left partial nephrectomy with guidance of intra-operative ultrasonography to delineate the lesion margins ( Figure 2A). Macroscopically, the tumour was 5 cm in largest dimension, fleshy with yellow-brown appearance possibly due to haemorrhage ( Figure 2B).
case_images: Haematoxylin and eosin staining of the tissue.. (
  A) Small round blue tumour cells arranged in sheets and nests infiltrating the adjacent stroma. Numerous hemosiderin laden macrophages are seen at the interface. No viable renal parenchyma is preserved, which is entirely replaced by dense fibrosis. Haematoxylin and eosin stain, x40; (
  B) Tumour cell morphology at higher magnification with high nuclear cytoplasmic ratio, inconspicuous cytoplasm and occasional mitoses. Haematoxylin and eosin stain, x400; (
  C) Tumour with adjacent bluish immature myxoid connective tissue. Haematoxylin and eosin stain, x400.
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case_images: The tumour cells were positive for vimentin, BCL2 and FL1, and negative for Pan CK, CK7, CD10, CD31, S100, HMB45, SMA, ER, PR and WT-1, suggestive of "primary undifferentiated renal sarcoma" with hematoma ( Figure 3 and Figure 4).
case_images: Immunohistochemical markers.. (
  A) Tumour cells with strong diffuse nuclear expression for FLI1. Immunohistochemistry with DAB counterstain, DAKO monoclonal antibody, x400; (
  B) Negative staining of tumour cells with CD99. Immunohistochemistry with DAB counterstain, DAKO monoclonal antibody, x400; (
  C) Strong diffuse staining of tumour cells for Vimentin. Immunohistochemistry with DAB counterstain, DAKO monoclonal antibody, x400; (
  D) Strong cytoplasmic and Golgi expression of WT1 and no nuclear expression in tumour cells. Immunohistochemistry with DAB counterstain, DAKO monoclonal antibody, x400; (
  E) Tumour cells showing strong cytoplasmic expression for Bcl2. Immunohistochemistry with DAB counterstain, DAKO monoclonal antibody, x400.
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case_images: The tumour cells were positive for vimentin, BCL2 and FL1, and negative for Pan CK, CK7, CD10, CD31, S100, HMB45, SMA, ER, PR and WT-1, suggestive of "primary undifferentiated renal sarcoma" with hematoma ( Figure 3 and Figure 4).
case_images: Follow-up contrast enhanced CT scan at 12 months showing no evidence of recurrence.
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case_images: At the last follow-up of 12 months, there is no evidence of recurrence on contrast enhanced computerised tomography scan ( Figure 5).