Author reply.

Sir,

I read with interest, the article “Solid renal masses in adults” by Mittal et al.[1] I would like to add as well as reiterate certain practical points with respect to the same. As mentioned by the authors, fat containing renal cell carcinoma (RCC) and angiomyolipomas (AML) are close differentials, especially in cases of lipid poor AML. Enhancement features on computed tomography (CT) are equivocal in differentiating these lesions. I would like to the recall the role of positron emission tomography (PET) CT in differentiating RCC and AML, as emphasized by Lin et al.[2] Of the 21 AMLs included in the study, none of them showed a maximum standardized uptake value (SUVmax) of more than 1.98.[2] Kim et al., in their study, found that 25 of the 27 RCC had SUVmax of >3.06 ± 0.45.[3]

As mentioned by the authors, intrarenal transitional cell carcinomas (TCC) and central RCCs are very close differentials and distinguishing them in imaging practice is difficult but essential. Findings such as tumor epicenter in collecting system, focal filling defect in renal pelvis, renal shape preservation, absence of cystic areas/necrosis, homogeneous contrast enhancement, and extension toward pelviureteric junction are quite favorable towards diagnosis of TCC, as established by Raza et al.[4]

Ultrasound elastography also appears to have a role in distinguishing benign and malignant lesions. Onur et al., in their study involving 71 solid renal masses, recognized that the mean strain index value of malignant lesions was significantly higher than that of benign lesions.[5]

Renal pseudotumors, especially nodular compensatory hypertrophy, may be diagnosed unequivocally using non contrast magnetic resonance imaging with diffusion weighted images.[67] Goyal et al. found that none of the pseudotumors showed restricted diffusion; whereas restricted diffusion was seen in all the solid RCCs. Diffusion weighted imaging with apparent diffusion coefficient values is very helpful in lesion characterization, especially in the setting of chronic kidney disease.

Nevertheless, as emphasized by the Mittal et al., lesion characterization by imaging is definitely difficult in smaller masses <1.5 cm, necessitating close monitoring with follow-up imaging.

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