CT of a renal mucinous tubular and spindle cell carcinoma

CT examination incidentally detected a tumor in the lower pole of left kidney in an asymptomatic 62-year-old male. Plain and contrast-enhanced CT scans were performed. Plain CT showed a high density lesion (21-56 HU, 7.6 cm × 6.0 cm) relative to renal parenchyma, presenting as a wellmarginated solid mass without a lobulated appearance and without fat (Figure 1A). Nodular and line shape calcification was observed in the mass (Figure 1B). Contrast-enhanced CT showed slight inhomogeneous enhancement of the mass (Figure 1C). Evaluation of the pattern of dynamic enhancement revealed the pattern of “lightly slow wash-in” (Figure 1C,DD). CT findings were suspicious for a solid renal malignant neoplasm.

Figure 1 A. Plain CT image shows a large tumor in the lower pole of left kidney with heterogeneous density, measuring 7.6 cm × 6.0 cm in size; B. Plain CT images shows line shape calcification at the margin of the mass (arrow) and nodular shape calcification in the mass (arrow head); C. Contrast-enhanced CT images of arterial phase (left) and venous phase (right) show slight enhancement of the mass and slightly patchy low attenuation in some areas of the mass (arrow); D. Contrast-enhanced CT images show the tumor part located in the kidney was less enhanced compared with normal renal parenchyma

The patient underwent nephrectomy. The nephrectomy specimen measured 18 cm × 13 cm × 5 cm. Grossly, the nephrectomy specimen revealed a well-circumscribed 7 cm × 7 cm × 5 cm renal mass, located in the lower pole of left kidney. The gross cut surface showed a fleshy texture with regions of grey-white, grey-yellow and greyred appearance (Figure 2A). The tumor was composed of tightly packed small bland tubules, spindle cells and partial mucinous stroma (Figure 2B). Immunohistochemistry was performed using standard methods. The tumor cells were positive for cytokeratins AE1/AE3, P504S, CD57, VIM, NSE, and negative for cytokeratins 34BE12/HCK, Act, CD10, CD117, CK34, CK7, Inhibin-a, VEGF. Ki-67 <10%.

Figure 2 A. Nephrectomy specimen displays a large welldemarcated tumor in the lower pole of the left kidney. The tumor is grey-yellow and grey-red in color, and bulges the contour of the involved kidney; B. Histological appearance of primary renal MTSCC, showing bland small tubules, spindle cells, and mucinous stroma

MTSCC is a new entity in pathological classification proposed by the WHO in recent years. With increased understanding and recognition of the tumor, it should be considered as a primary differential diagnostic possibility from sarcomatoid renal carcinoma.

Acknowledgements

Disclosure: The authors declare no conflict of interest.