Partial nephrectomy – nephron-sparing surgery – entails complete excision of the renal tumor with a margin of at least 0.5 cm of normal renal tissue and preservation of the largest amount of functioning renal parenchyma. Even though partial nephrectomy corresponds to nephron-sparing surgery, the last term includes different surgical techniques, namely, enucleation (nephron-sparing tumorectomy) reserved to benign tumors, polar resection or wedge resection with or without inclusion of the renal excretory tract (partial nephrectomy), or ex vivo resection. Some important changes in the manifestation of RCC have stimulated a growing trend toward nephron-sparing surgical techniques (Novic 1993). In particular, the widespread use of cross-sectional imaging techniques has led to a dramatic increase in the number of incidentally discovered small, asymptomatic renal masses. These asymptomatic tumors, which now constitute 25 % to almost 50 % of all surgically treated RCCs, are generally confined to the renal capsule, relatively small in size, and associated with an excellent prognosis after surgical removal (Konnak and Grossman 1985; Smith et al. 1989).

Partial nephrectomy is now considered the treatment of choice for small renal tumors of less than 4 cm in diameter in elective indication, especially if located in the renal poles or in the renal cortex far from the renal hilum and collecting system. The tumoral invasion of the collecting system represents an absolute contraindication to partial nephrectomy. Partial nephrectomy for hilar tumors (tumors in contact with a major renal vessel on preoperative cross-sectional imaging) is a cutting-edge procedure for which little data are available (Lattouf et al. 2008; Richstone et al. 2008). This surgical procedure avoids nephronic waste with an acceptable morbidity and similar oncologic outcomes compared to radical surgery. Radical nephrectomy presents a significantly higher risk for proteinuria due to hyperfiltration and chronic renal insufficiency in comparison to nephron-sparing surgery (Malcolm et al. 2009; Lau et al. 2000). Laparoscopic partial nephrectomy might allow a more aggressive approach in young healthy patients with an indeterminate mass.

Although radical nephrectomy was long considered the reference standard for the treatment of RCC, the results of numerous studies have demonstrated equivalent survival rates for patients who underwent radical nephrectomy and for those who underwent partial nephrectomy for small renal neoplasms (Lerner et al. 1996; Herr 1999; Lau et al. 2000; Ghavamian et al. 2002; Israel et al. 2006), with reported contralateral recurrence rates of <2 %, ipsilateral local recurrence and distant metastases of <5 %, and 5-year survival rates of 87–90 %, which are comparable to those from radical nephrectomy. Some authors are pushing the limit for partial nephrectomy above the threshold of 4 cm, and more surgeons are either considering anatomical location or technical expected difficulties rather than just the tumor size. Nephron-sparing surgery leads to higher risk of bleeding, especially in case of tumors larger than 4 cm, and it is absolutely necessary to investigate thoroughly the vascularization of the tumor to avoid such complications with exhaustive and accurate preoperative imaging (Peycelon et al. 2009).

The other most important present applications of partial nephrectomy are malignant renal tumors in a solitary functioning kidney in patients with congenitally absent kidney or who had previously undergone contralateral nephrectomy for RCC, malignant tumors in patients with compromised renal function, or multicentric bilateral malignant renal tumors (Provet et al. 1991; Light and Novick 1993). Multiple RCCs can be sporadic in 4–15 % cases, but are much more common in patients with von Hippel–Lindau disease and hereditary RCC (Sheth et al. 2001). In these patients, RCCs are often bilateral, multifocal, and manifest at a younger age. The challenge is to detect and delineate all lesions to ensure complete surgical excision, while preserving the maximal amount of functioning parenchyma. Nephron-sparing surgery has also been performed in young patients with bilateral synchronous Wilms’ tumor (Davidoff et al. 2008). Residual applications of partial nephrectomy correspond to large benign tumors, renal traumas, renal staghorn calculosis, complicated calyceal diverticula, renal duplications with segmental hydronephrosis, and complicated renal tuberculosis.

The appearance of the postoperative kidney depends to a great extent on the size and location of the resected tumor (Israel et al. 2006) and on the imaging time delay after resection. After partial nephrectomy, the kidney presents an abnormal contour (Fig. 4) and presents a posterior displacement adhering to the posterior abdominal wall. This finding, especially if accompanied by reactive or fibrotic changes in the perinephric fat, is indicative of previous renal surgery (Israel et al. 2006). Evidence of surgical metallic clips, visualized on CT or MR by using in-phase and out-of-phase sequences, represents a further usual imaging feature after partial nephrectomy. Several techniques are used for partial resection, which may also include packing the postsurgical defect with fat (Baumgarten and Baumgartner 2000) to help achieve hemostasis. If fat packing (Figs. 5 and 6) is used, the resulting appearance may mimic renal tumors by both CT (angiomyolipoma) and US (angiomyolipoma or hyperechoic RCC). Over time, the volume of fat used for surgical packing may decrease or remain unchanged, while the kidney is usually displaced posteriorly adjacent to the posterior abdominal wall (Fig. 6) (Israel et al. 2006). Extensive postoperative reactive changes in the retroperitoneum are also frequently visible (Figs. 7 and 8) and help in the differential diagnosis from fatty renal tumors.

Biologically absorbable hemostatic agents (Fig. 9) may also be used to help control intraoperative bleeding (Israel et al. 2006). Such materials may contain air pockets or bubbles (Fig. 10) that, on early postoperative images, may resemble a focal abscess (Young et al. 1993; Israel et al. 2006). To differentiate between a collection that consists of a hemostatic agent containing air bubbles and one that consists of infected fluid containing gas bubbles, it is necessary to consider the imaging findings in combination with the patient’s clinical history and symptoms (Israel et al. 2006). Anyway, some imaging findings may be important for the differential diagnosis. In most cases, the air in a hemostatic agent is rapidly resorbed during the first postsurgical week, even though air bubbles can be identified on images even 1 month after surgery (Fig. 10). In-phase and opposed-phase gradient echo MR sequences may be employed to detect the susceptibility artifact related to the surgical clips. The hemostatic agent typically reveals tightly packed gas bubbles with a geometric shape. The presence of an abscess should be suspected if a localized fluid collection that has an enhanced rim and contains gas bubbles or a gas–fluid level is seen. In addition, decreased density of the nephrogram because of edema in the surrounding renal parenchyma supports the diagnosis of an abscess.

Even though radical nephrectomy is a more simple surgical procedure if compared to nephron-sparing surgery, both techniques may present postoperative complications and not related to tumoral recurrence which are classified as early (within 30 days from surgery) and late (30 days to 1 year from surgery) complications. The most common early complications are acute or progressive renal failure and proteinuria, even though these complications do not present typical imaging features. Other complications include pneumothorax (especially if a thoracoabdominal approach is used), trauma to adjacent structures (inferior vena cava, colon, duodenum, spleen, or pancreatic tail), lateral hernia when a flank incision is used, and postsurgical collections.