# Radiologic Evaluation of Small Renal Masses (II): Posttreatment Management

Authors: J. Santos; C. Deltoro; M. I. Martín; A. Marhuenda
Journal: Advances in Urology
 (2008)

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## Abstract

The increase in the detection of small renal masses (SRMs) and their best knowledge leads to a change in the therapeutic management of these lesions. The use of a less aggressive surgical technique or even an expectant attitude is the current tendency, in order to preserve as much renal function as possible. Imaging techniques are essential in the followup of these lesions. It allows us to know the postsurgical changes and possible complications due to treatment and the presence of local recurrence and metastases. Furthermore, a close radiological followup of SRM related to ablative treatments is mandatory. The purpose of this article is to reveal the imaging features of complications due to surgical or ablative treatments, local recurrence and metastasis, as well as their followup.


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## Body

## 1. Imaging Followup of SRM

Several authors have
reported that small incidentally detected tumors are associated
with better survival outcomes. The 5-year disease-free survival rate for
incidental renal tumors of <4 cm treated with radical or partial nephrectomy is 95%–100%. There is a clear
increased rate of metastases in patients found to have
renal cell carcinoma (RCC) >3 cm in maximum dimension at autopsy compared to those
with RCCs of < or =3 cm [1, 2].Silverman et al. [3] have established the indications for percutaneous biopsy of renal masses in patients  with a renal mass and known
extrarenal primary malignancy, imaging findings that suggest unresectable renal
cancer, surgical comorbidity, those that may have been caused by an infection. Emerging
indications are patients with a small (<3 cm) hyperattenuating, homogeneusly enhancing
renal mass, those with a renal mass considered for percutaneus ablation and
patients with an indeterminate cystic renal mass.After surgical treatment, radical nephrectomy (RN) or
partial nephrectomy (PN), about 20%–30% of patients with localized renal
tumors relapse [4]. The recurrences occur
three years after surgery, with a median time to relapse being 1 to 2 years. In
multifocal renal cortical tumors, local recurrences rates following elective
partial nephectomy are from 0% to 10% with a risk of local recurrence for
tumors of 4 cm or less [5]. However, late tumor recurrences
can occur many years after treatment. The lung is the most vulnerable site for
distant recurrence (50%–60% of patients) [6].
Other sites of recurrence are bone, surgical site, brain, liver, and the
contralateral kidney.There are multiple prognostic factors to predict recurrence after
surgery. A postoperative prognostic nomogram has been published predicting
recurrence for patients with conventional clear cell renal cell carcinoma [7], and
it can be useful for patient counselling, clinical trial, and effective patient
followup strategies.Greatest tumor diameter, T stage, stage group, and nuclear grade are
important factors in determining the likelihood of recurrence. At the present
time, active surveillance of small renal masses is an experimental approach,
but represents an attractive option for elderly patients and those with
significant comorbidity.Bilateral multifocal renal tumors are present in approximately 5% of
patients with sporadic renal tumors [8]. Conventional clear cell carcinoma is the
most common histologic subtype, followed by papillary carcinoma [5]. Most of them can be synchronous but asynchronous lesions
may occur many years after the initial nephrectomy, and that is why a long-term
followup. must be maintained.In imaging followup evaluation of kidney cancer, CT is the modality of choice for
detection of local recurrence and distant metastases. In patients with
compromised renal function or with contraindications to iodinated contrast,
gadolinium-enhanced MR imaging of the abdomen and pelvis may be used. Also a
chest radiograph or chest CT study can be performed for surveillance of
pulmonary metastasis.Renal cysts are common
benign lesions and are often an incidental finding during abdominal CT, (see the
appendix) [9]. If they are of fluid attenuation, lack internal
architecture, have thin walls, and show no evidence of enhancement after IV
contrast administration, they can be easily dismissed as benign. However, the
appearance of moderately complex or mild renal cyst varies and can cause
difficulties in diagnosis and management. The Bosniak classification or renal
cysts has proven to be a useful tool in helping to evaluate these lesions and
decide clinical management [10]. In 1993,
Bosniak revised the original classification system [11] to include a subset of category II lesions, category IIF
lesions (“F” for followup).CT studies are an
effective way of managing patients with moderately complex cystic lesions of
the kidney (Bosniak category IIF) because the absence of change supports
benignity and progression indicates neoplasm. Alternatively, MRI may prove
helpful in the characterization of these lesions and may possibly avoid the
need for followup examinations in these cases [12]. In these
lesions considered to be category IIF, the followup examinations are necessary
to prove stability and, therefore, benignity. The first followup examination is
recommended 6 months after the initial examination. If the lesion is unchanged,
additional followup examinations should be performed at yearly intervals for at
least 5 years, although the optimal followup period has not been determined. However,
in younger patients, a longer followup period may be necessary.45% of the patients with von Hippel-Lindau disease will have a renal
adenocarcinoma, often (80%) multifocal or bilateral. Treatment must be as
conservative as possible because of the multifocality and its usual low grade.
The risk of recidive is very high: 30% at 5 years, 80% at 10 years,
therefore, they must be followed up strictly and regularly (Figure1) [13].37-year old woman with von Hipple Lindau
disease. Radical right nefrectomy and partial tumorectomy in left kidney. (a) Axial contrast-enhanced CT scan shows scar
in the lower pole in the left kidney (arrow),
without any mass. Note the absence of right kidney. (b) One year later sagittal US scan
with a large mass less echogenic than renal sinus fat, involving the lower pole
parenchyma (arrows). (c) Axial contrast-enhanced CT
(nephrographic phase) scan obtained at the same time shows the mass that has
grown with perinephric extension (white arrow). It was a renal adenocarcinoma.
Note of the presence of paraaorthic lymph node (black arrow).
(a)(b)(c)


## 2. Imaging of Complications of Partial Nephrectomy

The standard treatment for renal cell carcinoma was,
for many years, radical nephrectomy, but over the past 10 years, there has been
a trend toward the use of nephron-sparing surgery to treat renal cell
carcinoma. The results of numerous studies have demonstrated equivalent cancer
survival rates for patients who underwent radical nephrectomy and those who
underwent partial nephrectomy for small renal neoplasms [14–16].The procedure can be performed by using open or
laparoscopic techniques. However, partial nephrectomy with laparoscopic
techniques is a more complex operation than the traditional radical nephrectomy
and higher complication rates have been reported [17].It is important to know normal findings and imaging
features of postsurgical complications after partial nephrectomy, for
appropriate postoperative management.


### 2.1. Postoperative Appearance

The appearance of the postoperative kidney depends on the size and
location of the resected tumor. After partial nephrectomy for a small
peripheral tumor, a wedge-shaped defect in the renal parenchyma is typically
visible at CT and MR imaging. The postoperative
kidney usually has a more posterior location and abuts to the posterior
abdominal wall (Figure2). Perinephric fat
maybe packed into the surgical bed to help achieve haemostasis. This material
may be mistaken for a fatty mass such as an AML.Figure 2
Postoperative findings after
laparoscopic left partial nephrectomy, image shows a posterior location of the
left kidney, which abuts the posterior abdominal wall.To help control intraoperative bleeding, biologically absorbable
haemostatic agents also may be used. Such materials may contain bubbles or air
pockets that may resemble a focal abscess. The possible presence of a
haemostatic agent should be considered if a linear arrangement of air bubbles
is noted or if air bubbles maintain the same position on subsequent images. In
most cases, the air in a haemostatic agent is rapidly reabsorbed during the first
postsurgical week. However, in some cases, air bubbles can be identified on
images even 1 month after surgery. 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 intensity of
the nephrogram because of edema in the surrounding renal parenchyma supports
the diagnosis of an abscess. Of course it is necessary to consider the imaging
findings in combination with the patient’s clinical history and symptoms [18–20].The biologically absorbable haemostatic agents may also mimic a
pseudotumor that can lead to confusion. Several cases have been reported on
literature after nephron-sparing surgery using gelatine bio absorbable sponge.
They were seen as solid masses, with regular borders and enhancement after
injection of intravenous contrast agent, due to the presence on granulomatous
tissue surrounding the haemostatic material. In all the cases there was a
complete resolution of such lesions in an average time of thirteen months [21, 22].


### 2.2. Complications

Complications seen on
partial nephrectomy can be divided into vascular complications, complications
in the collecting system, infection, recurrent tumor and complications due to
technical factors [20].


#### 2.2.1. Vascular Complications

During partial nephrectomy, the renal
hiliar vessels must be temporarily clamped to ensure a bloodless surgical
field; however, clamping may injure the arterial intima and lead to thrombosis.
If that complication is not recognized at the time of surgery or in the
immediate postoperative period, renal infarction and atrophy will occur.
Complications related to injury of the intrarenal arteries in the surgical bed
may also occur. A hematoma may result if the suturing of transected blood
vessels is inadequate (Figure3). A pseudoaneurysm may result from injury to an
intrarenal artery at the surgical site or to the main renal artery or one of
its major branches [23–25].Figure 3
Hematoma after open right partial nephrectomy. Mass with attenuation of 60HU that extends from
postoperative bed to the perinephric space.


#### 2.2.2. Complications in the Collecting System

When calyceal entry is necessary, it
would have to be repaired in order to avoid urinary leakage. If the repair is
not watertight, a urine leak may occur into the surgical bed. Such leakage may
have the appearance of a simple fluid collection in the perirenal space [26], or
it may have a more heterogeneous appearance if it contains blood products. This
complication can be diagnosed on the basis of contrast-enhanced CT and MR
images acquired during the excretory phase, with the observation of contrast
material leakage from the collecting system into the surgical bed. In most
cases, the fluid collection resolves either spontaneously or after placement of
a ureteral stent or nephrostomy catheter. Less commonly, urinary leakage
persists and an urinoma forms [20].


#### 2.2.3. Infection

A fluid collection in the surgical bed may become infected, and an abscess may
develop. With imaging techniques alone, it may be difficult to differentiate an
infected fluid collection from an uninfected one. Moreover, as mentioned
before, the presence of air bubbles in a bioabsorbable haemostatic agent may
further complicate the interpretation of imaging studies. However, patients
with a postoperative abscess are likely to manifest clinical symptoms and signs
suggestive of infection; in such cases, a needle aspiration is performed for
laboratory analysis, followed by drainage if necessary. In addition, patients
who have undergone a partial nephrectomy may present with symptoms
of pyelonephritis, which may appear as a striated or heterogeneous nephrogram
and may be difficult to differentiate from renal infarction on images alone [20].


#### 2.2.4. Complications Due to Technical Factors

During partial nephrectomy, the liver
or spleen may be inadvertently lacerated or contused by surgical instruments
used to keep adjacent organs away from the surgical field. Such injuries may be
detected with CT and MR imaging. In addition, hernias may occur at the incision
site and may contain portions of the bowel or other abdominal organs [26].


## 2.1. Postoperative Appearance

The appearance of the postoperative kidney depends on the size and
location of the resected tumor. After partial nephrectomy for a small
peripheral tumor, a wedge-shaped defect in the renal parenchyma is typically
visible at CT and MR imaging. The postoperative
kidney usually has a more posterior location and abuts to the posterior
abdominal wall (Figure2). Perinephric fat
maybe packed into the surgical bed to help achieve haemostasis. This material
may be mistaken for a fatty mass such as an AML.Figure 2
Postoperative findings after
laparoscopic left partial nephrectomy, image shows a posterior location of the
left kidney, which abuts the posterior abdominal wall.To help control intraoperative bleeding, biologically absorbable
haemostatic agents also may be used. Such materials may contain bubbles or air
pockets that may resemble a focal abscess. The possible presence of a
haemostatic agent should be considered if a linear arrangement of air bubbles
is noted or if air bubbles maintain the same position on subsequent images. In
most cases, the air in a haemostatic agent is rapidly reabsorbed during the first
postsurgical week. However, in some cases, air bubbles can be identified on
images even 1 month after surgery. 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 intensity of
the nephrogram because of edema in the surrounding renal parenchyma supports
the diagnosis of an abscess. Of course it is necessary to consider the imaging
findings in combination with the patient’s clinical history and symptoms [18–20].The biologically absorbable haemostatic agents may also mimic a
pseudotumor that can lead to confusion. Several cases have been reported on
literature after nephron-sparing surgery using gelatine bio absorbable sponge.
They were seen as solid masses, with regular borders and enhancement after
injection of intravenous contrast agent, due to the presence on granulomatous
tissue surrounding the haemostatic material. In all the cases there was a
complete resolution of such lesions in an average time of thirteen months [21, 22].


## 2.2. Complications

Complications seen on
partial nephrectomy can be divided into vascular complications, complications
in the collecting system, infection, recurrent tumor and complications due to
technical factors [20].


### 2.2.1. Vascular Complications

During partial nephrectomy, the renal
hiliar vessels must be temporarily clamped to ensure a bloodless surgical
field; however, clamping may injure the arterial intima and lead to thrombosis.
If that complication is not recognized at the time of surgery or in the
immediate postoperative period, renal infarction and atrophy will occur.
Complications related to injury of the intrarenal arteries in the surgical bed
may also occur. A hematoma may result if the suturing of transected blood
vessels is inadequate (Figure3). A pseudoaneurysm may result from injury to an
intrarenal artery at the surgical site or to the main renal artery or one of
its major branches [23–25].Figure 3
Hematoma after open right partial nephrectomy. Mass with attenuation of 60HU that extends from
postoperative bed to the perinephric space.


### 2.2.2. Complications in the Collecting System

When calyceal entry is necessary, it
would have to be repaired in order to avoid urinary leakage. If the repair is
not watertight, a urine leak may occur into the surgical bed. Such leakage may
have the appearance of a simple fluid collection in the perirenal space [26], or
it may have a more heterogeneous appearance if it contains blood products. This
complication can be diagnosed on the basis of contrast-enhanced CT and MR
images acquired during the excretory phase, with the observation of contrast
material leakage from the collecting system into the surgical bed. In most
cases, the fluid collection resolves either spontaneously or after placement of
a ureteral stent or nephrostomy catheter. Less commonly, urinary leakage
persists and an urinoma forms [20].


### 2.2.3. Infection

A fluid collection in the surgical bed may become infected, and an abscess may
develop. With imaging techniques alone, it may be difficult to differentiate an
infected fluid collection from an uninfected one. Moreover, as mentioned
before, the presence of air bubbles in a bioabsorbable haemostatic agent may
further complicate the interpretation of imaging studies. However, patients
with a postoperative abscess are likely to manifest clinical symptoms and signs
suggestive of infection; in such cases, a needle aspiration is performed for
laboratory analysis, followed by drainage if necessary. In addition, patients
who have undergone a partial nephrectomy may present with symptoms
of pyelonephritis, which may appear as a striated or heterogeneous nephrogram
and may be difficult to differentiate from renal infarction on images alone [20].


### 2.2.4. Complications Due to Technical Factors

During partial nephrectomy, the liver
or spleen may be inadvertently lacerated or contused by surgical instruments
used to keep adjacent organs away from the surgical field. Such injuries may be
detected with CT and MR imaging. In addition, hernias may occur at the incision
site and may contain portions of the bowel or other abdominal organs [26].


## 2.2.1. Vascular Complications

During partial nephrectomy, the renal
hiliar vessels must be temporarily clamped to ensure a bloodless surgical
field; however, clamping may injure the arterial intima and lead to thrombosis.
If that complication is not recognized at the time of surgery or in the
immediate postoperative period, renal infarction and atrophy will occur.
Complications related to injury of the intrarenal arteries in the surgical bed
may also occur. A hematoma may result if the suturing of transected blood
vessels is inadequate (Figure3). A pseudoaneurysm may result from injury to an
intrarenal artery at the surgical site or to the main renal artery or one of
its major branches [23–25].Figure 3
Hematoma after open right partial nephrectomy. Mass with attenuation of 60HU that extends from
postoperative bed to the perinephric space.


## 2.2.2. Complications in the Collecting System

When calyceal entry is necessary, it
would have to be repaired in order to avoid urinary leakage. If the repair is
not watertight, a urine leak may occur into the surgical bed. Such leakage may
have the appearance of a simple fluid collection in the perirenal space [26], or
it may have a more heterogeneous appearance if it contains blood products. This
complication can be diagnosed on the basis of contrast-enhanced CT and MR
images acquired during the excretory phase, with the observation of contrast
material leakage from the collecting system into the surgical bed. In most
cases, the fluid collection resolves either spontaneously or after placement of
a ureteral stent or nephrostomy catheter. Less commonly, urinary leakage
persists and an urinoma forms [20].


## 2.2.3. Infection

A fluid collection in the surgical bed may become infected, and an abscess may
develop. With imaging techniques alone, it may be difficult to differentiate an
infected fluid collection from an uninfected one. Moreover, as mentioned
before, the presence of air bubbles in a bioabsorbable haemostatic agent may
further complicate the interpretation of imaging studies. However, patients
with a postoperative abscess are likely to manifest clinical symptoms and signs
suggestive of infection; in such cases, a needle aspiration is performed for
laboratory analysis, followed by drainage if necessary. In addition, patients
who have undergone a partial nephrectomy may present with symptoms
of pyelonephritis, which may appear as a striated or heterogeneous nephrogram
and may be difficult to differentiate from renal infarction on images alone [20].


## 2.2.4. Complications Due to Technical Factors

During partial nephrectomy, the liver
or spleen may be inadvertently lacerated or contused by surgical instruments
used to keep adjacent organs away from the surgical field. Such injuries may be
detected with CT and MR imaging. In addition, hernias may occur at the incision
site and may contain portions of the bowel or other abdominal organs [26].


## 3. Imaging of Local Recurrence

The most important risk factor for recurrence is the surgical stage of renal cell
carcinoma at the time of diagnosis, being for large tumors a bigger incidence
than for small ones. However, size is not of prognostic value if capsule is not
invaded (13). Patients with positive
nodes at surgery relapse sooner, and factors like a high Fuhrman grade on
histopathology, and collecting duct carcinoma spindled (sarcomatoid)
tumor architecture also adversely influence prognosis [27]. Recurrence must
be differentiated from postsurgical fibrosis (Figure 4) and multifocality within
the kidney, probably more often seen since small renal tumors are managed with conservative
surgical techniques (Figure 5) [13].Figure 4
Fibrosis. Axial post contrast T1 with fat
saturation shows a hipointense lesion on the lateral aspect of the left kidney
that does not enhance with gadolinium, revealing post surgical changes.Local recurrence. (a) Axial contrast enhanced CT scan showing
the postsurgical changes on the right lumbar fosse with removal of the kidney
and migration of the right colon to the nephrectomy fosse. Note the second
small renal lesion on the anterior pole of the left kidney, probably due to
multifocality that was not advertised on the previous studies of the patient (arrow).
(b) A soft tissue mass on the medial aspect of
the left kidney at the site of the previous enucleation resection with
enhancing nodules around the kidney and adjacent to the psoas. (c) Enhanced
nodules adjacent to the diaphragm muscle (arrows).
(a)(b)(c)The possibility of local recurrence
in the remaining kidney is the main limitation of nephron-sparing surgery in
patients with renal-cell carcinoma. Local recurrence occurs in about 5% of
patients, and has been related to cancer multifocality, incomplete resection of
the primary tumor, positive surgical margins, or regional lymph node
metastasis. Some authors reported that the type of surgical intervention
(enucleation, enucleoresection and resection) does not affect the frequency of
tumor local recurrence [28].Recurrence usually occurs within the first five years after surgery, but
late recurrence has been related to renal cancer and long-term followup after a
nephrectomy is mandatory for patients with perinephric invasion of a renal cell
carcinoma due to the risk of renal fosse recurrence [29].
Followup of these patients is usually made by CT but also MRI for selected cases, as
mentioned in the previous article and, in both techniques, arterial phase
scanning is essential for maximizing lesion conspicuity, followed by
a portal venous phase. Owing to the increased risk of these patients for
additional renal primary carcinomas, the renal fosse and remaining
kidney must be carefully evaluated looking for a recurrence.


### 3.1. Local Recurrence in Renal Fosse after Nefrectomy

Recurrent cancer after
nephron-sparing surgery can be suggested when an enhancing nodule
develops in the wedge-shaped partial nephrectomy defect. After radical
nephrectomy at imaging, retroperitoneal anatomy is significantly altered after
surgical removal of the kidney. Small bowel, spleen, pancreas, and colon may
migrate into the nephrectomy fosse [30] (Figure 5(a)).At partial nephrectomy if an adequate margin is not obtained and
surgical excision is incomplete, the growth of any remaining neoplastic cells
at the resection site over time may result in tumor recurrence in the surgical
bed. Even if a tumor is completely excised, it may recur if tumor cells are
spilled into the surgical field at the time of resection.Alternatively, in a patient with multiple foci of disease, an apparent
tumor recurrence may actually be an additional preexistent renal cell carcinoma
that either was not depicted at preoperative imaging studies or was not
identified intraoperatively [23]. The surgical field of view during laparoscopic
partial nephrectomy is limited, and the surgeon can see only a small portion of
the kidney. This limitation may lead to a failure to identify a specific small
renal tumor if there is more than one small lesion in the vicinity. Unless
previous imaging studies are carefully reviewed, the latter then might be
misidentified as a recurrent lesion.The radiologic
presentation of a recurrent renal carcinoma after surgery appears as an
enhancingmass in the surgical site. The recurrence often involves
the quadratus lumborum and psoas muscles andcan displace
or invade nearby structures, even the spine. The cephalic extent may
reach the adrenal bed or may involve the ipsilateral adrenal gland
if the latter was spared at the time of nephrectomy [31].Moreover, as mentioned
earlier, bioabsorbable haemostatic agents may be seen as pseudotumor, so, a
close followup examination is required to see the evolution.


### 3.2. Local Recurrence and Residual Disease after Thermal Ablation

Early detection of a
recurrence following initial treatment is mandatory for any
surveillance protocol, and it is essential to review the preablation and
ablation images for a good interpretation of followup images.
Imaging must be carefully evaluated to determine the initial tumor size, tumor
location, and electrode placement in an effort to predictare as
that are likely to demonstrate recurrence. Eccentric electrodeplacement
within a mass is likely to result in residual disease at the tumor
margin farthest from the ablation device tip. Occasionally,
a new tumor focus may develop.As with local
recurrence, residual tumor is suggested when enhancing nodules or crescents areas
noted in the vicinity of the treated tumor on contrast enhanced CT or MR
images. Furthermore, gadolinium-enhanced fat-suppressed T1-weighted
subtraction MR images are helpful in demonstrating subtle areas of
enhancement by eliminating the high signal intensity often present
within the tumor on unsubtracted images. Because the ablation zone
following RF ablation typically has low signal intensity on
T2-weighted MR images, a new or enlarging focus of hyperintensity on
these images may also be a sign of viable tumor.Ablated tumors remain
stable in size or involute over time on followup images. Therefore,
an increase in tumor size after the acute postablation changes have
resolved should raise concern
for tumor recurrence, as well as within the renal vein and inferior vena cava, even in the
electrode insertion site [30].


## 3.1. Local Recurrence in Renal Fosse after Nefrectomy

Recurrent cancer after
nephron-sparing surgery can be suggested when an enhancing nodule
develops in the wedge-shaped partial nephrectomy defect. After radical
nephrectomy at imaging, retroperitoneal anatomy is significantly altered after
surgical removal of the kidney. Small bowel, spleen, pancreas, and colon may
migrate into the nephrectomy fosse [30] (Figure 5(a)).At partial nephrectomy if an adequate margin is not obtained and
surgical excision is incomplete, the growth of any remaining neoplastic cells
at the resection site over time may result in tumor recurrence in the surgical
bed. Even if a tumor is completely excised, it may recur if tumor cells are
spilled into the surgical field at the time of resection.Alternatively, in a patient with multiple foci of disease, an apparent
tumor recurrence may actually be an additional preexistent renal cell carcinoma
that either was not depicted at preoperative imaging studies or was not
identified intraoperatively [23]. The surgical field of view during laparoscopic
partial nephrectomy is limited, and the surgeon can see only a small portion of
the kidney. This limitation may lead to a failure to identify a specific small
renal tumor if there is more than one small lesion in the vicinity. Unless
previous imaging studies are carefully reviewed, the latter then might be
misidentified as a recurrent lesion.The radiologic
presentation of a recurrent renal carcinoma after surgery appears as an
enhancingmass in the surgical site. The recurrence often involves
the quadratus lumborum and psoas muscles andcan displace
or invade nearby structures, even the spine. The cephalic extent may
reach the adrenal bed or may involve the ipsilateral adrenal gland
if the latter was spared at the time of nephrectomy [31].Moreover, as mentioned
earlier, bioabsorbable haemostatic agents may be seen as pseudotumor, so, a
close followup examination is required to see the evolution.


## 3.2. Local Recurrence and Residual Disease after Thermal Ablation

Early detection of a
recurrence following initial treatment is mandatory for any
surveillance protocol, and it is essential to review the preablation and
ablation images for a good interpretation of followup images.
Imaging must be carefully evaluated to determine the initial tumor size, tumor
location, and electrode placement in an effort to predictare as
that are likely to demonstrate recurrence. Eccentric electrodeplacement
within a mass is likely to result in residual disease at the tumor
margin farthest from the ablation device tip. Occasionally,
a new tumor focus may develop.As with local
recurrence, residual tumor is suggested when enhancing nodules or crescents areas
noted in the vicinity of the treated tumor on contrast enhanced CT or MR
images. Furthermore, gadolinium-enhanced fat-suppressed T1-weighted
subtraction MR images are helpful in demonstrating subtle areas of
enhancement by eliminating the high signal intensity often present
within the tumor on unsubtracted images. Because the ablation zone
following RF ablation typically has low signal intensity on
T2-weighted MR images, a new or enlarging focus of hyperintensity on
these images may also be a sign of viable tumor.Ablated tumors remain
stable in size or involute over time on followup images. Therefore,
an increase in tumor size after the acute postablation changes have
resolved should raise concern
for tumor recurrence, as well as within the renal vein and inferior vena cava, even in the
electrode insertion site [30].


## 4. Followup Imaging after Radiofrequency Ablation of SRM

There has been a clear increase in the incidence of RCC during the past 10 years, as
a result of an increased rate of incidental detection of renal neoplasm. It has
been reported that radiofrequency ablation can completely destroy renal
cancers, while transmitting minimal collateral damage to surrounding renal
parenchyma [32].Radiofrequency ablation is a safe
effective treatment for small renal-cell carcinoma (RCC) in selected patients
who are not good operative candidates. Small size and noncentral location are
favorable tumor characteristics (large tumors can sometimes be successfully
treated but could result in an increased risk of residual RCC). After ablation,
computed tomography or magnetic resonance imaging is used to confirm complete
eradication or the presence of residual unablated tumor. When the appearance of
the ablated tumor deviates from expected findings, percutaneous biopsy is
necessary to further evaluate the ablation zone [33].


### 4.1. Imaging Followup

All patients must undergo contrast-enhanced imaging (MRI or CT) before
radiofrequency ablation as a baseline comparison for subsequent imaging after
ablation (initial tumor control).


#### 4.1.1. CT Imaging

CT scan of the kidney must be obtained
immediately after the ablation session to assess tumor destruction. Normal
tissue shows enhancement, with no enhancement in treated area, which
encompasses tumor. Small gas bubbles are seen in area of treatment, this is an
expected finding resulting from tissue boiling during ablation [34]. After
ablation an initial CT scan, imaging followup without and with contrast agent
must be performed after 1 month, 3 months, and 6 months and subsequent followup
will depend on the clinical condition of the patient and the comorbid
conditions, generally at 6 to 12 month interval. Enhancement of any portion of
the tumor must be considered residual viable tumor, and the absence of
enhancement as no evidence of disease (complete necrosis and thus completely
ablated tumor). Images must also be reviewed for the presence of any new
metastatic disease or new renal cell carcinomas [34, 35].


#### 4.1.2. MR Imaging

A considerable number of patients of eligible patients cannot receive contrast
agents that contain iodine because of preexisting impaired renal function or
severe contrast material allergies. These patients are usually referred for
contrast enhanced magnetic resonance (MR) imaging of the kidney. As in CT
imaging, followup MR imaging must be performed in all patients immediately
after the completion of the RF ablation. At T2-weighted fast SE images
performed, the ablation zone, in all cases appear as a round or ovoid
hypointense region that replaces the intermediate or high signal intensity
tumor seen on the preablation image. The hypointense thermal ablation zone is
surrounded by a bright rim with a well-defined outer border. Thin rim
enhancement is noted in all contrast-enhanced MR images [36].Followup MR imaging must be
performed every 3 months during the first year after ablation and every 6
months thereafter.Tumor recurrence is defined as the
appearance of hyperintense soft-tissue signal within the ablation zone or along
its margin on T2-weighted or STIR MR images or as areas of abnormal contrast
enhancement within the treated region on the postcontrast images [37].


## 4.1. Imaging Followup

All patients must undergo contrast-enhanced imaging (MRI or CT) before
radiofrequency ablation as a baseline comparison for subsequent imaging after
ablation (initial tumor control).


### 4.1.1. CT Imaging

CT scan of the kidney must be obtained
immediately after the ablation session to assess tumor destruction. Normal
tissue shows enhancement, with no enhancement in treated area, which
encompasses tumor. Small gas bubbles are seen in area of treatment, this is an
expected finding resulting from tissue boiling during ablation [34]. After
ablation an initial CT scan, imaging followup without and with contrast agent
must be performed after 1 month, 3 months, and 6 months and subsequent followup
will depend on the clinical condition of the patient and the comorbid
conditions, generally at 6 to 12 month interval. Enhancement of any portion of
the tumor must be considered residual viable tumor, and the absence of
enhancement as no evidence of disease (complete necrosis and thus completely
ablated tumor). Images must also be reviewed for the presence of any new
metastatic disease or new renal cell carcinomas [34, 35].


### 4.1.2. MR Imaging

A considerable number of patients of eligible patients cannot receive contrast
agents that contain iodine because of preexisting impaired renal function or
severe contrast material allergies. These patients are usually referred for
contrast enhanced magnetic resonance (MR) imaging of the kidney. As in CT
imaging, followup MR imaging must be performed in all patients immediately
after the completion of the RF ablation. At T2-weighted fast SE images
performed, the ablation zone, in all cases appear as a round or ovoid
hypointense region that replaces the intermediate or high signal intensity
tumor seen on the preablation image. The hypointense thermal ablation zone is
surrounded by a bright rim with a well-defined outer border. Thin rim
enhancement is noted in all contrast-enhanced MR images [36].Followup MR imaging must be
performed every 3 months during the first year after ablation and every 6
months thereafter.Tumor recurrence is defined as the
appearance of hyperintense soft-tissue signal within the ablation zone or along
its margin on T2-weighted or STIR MR images or as areas of abnormal contrast
enhancement within the treated region on the postcontrast images [37].


## 4.1.1. CT Imaging

CT scan of the kidney must be obtained
immediately after the ablation session to assess tumor destruction. Normal
tissue shows enhancement, with no enhancement in treated area, which
encompasses tumor. Small gas bubbles are seen in area of treatment, this is an
expected finding resulting from tissue boiling during ablation [34]. After
ablation an initial CT scan, imaging followup without and with contrast agent
must be performed after 1 month, 3 months, and 6 months and subsequent followup
will depend on the clinical condition of the patient and the comorbid
conditions, generally at 6 to 12 month interval. Enhancement of any portion of
the tumor must be considered residual viable tumor, and the absence of
enhancement as no evidence of disease (complete necrosis and thus completely
ablated tumor). Images must also be reviewed for the presence of any new
metastatic disease or new renal cell carcinomas [34, 35].


## 4.1.2. MR Imaging

A considerable number of patients of eligible patients cannot receive contrast
agents that contain iodine because of preexisting impaired renal function or
severe contrast material allergies. These patients are usually referred for
contrast enhanced magnetic resonance (MR) imaging of the kidney. As in CT
imaging, followup MR imaging must be performed in all patients immediately
after the completion of the RF ablation. At T2-weighted fast SE images
performed, the ablation zone, in all cases appear as a round or ovoid
hypointense region that replaces the intermediate or high signal intensity
tumor seen on the preablation image. The hypointense thermal ablation zone is
surrounded by a bright rim with a well-defined outer border. Thin rim
enhancement is noted in all contrast-enhanced MR images [36].Followup MR imaging must be
performed every 3 months during the first year after ablation and every 6
months thereafter.Tumor recurrence is defined as the
appearance of hyperintense soft-tissue signal within the ablation zone or along
its margin on T2-weighted or STIR MR images or as areas of abnormal contrast
enhancement within the treated region on the postcontrast images [37].


## 5. Followup Cryosurgycal Ablation of SRM

Concomitantly with the change in presentation of renal
masses there is a paradigm shift in the management of localized small renal
lesions. Minimally invasive options such as cryoablation have emerged as an
alternative surgical option for selected patients. The potential complications
of nephron-sparing kidney surgery make renal cryoablation an appealing option
in high-risk surgical populations.Cryoablation requires real-time
monitoring of the ice ball by ultrasound,
CT, or magnetic resonance imaging (MRI), to ensure that the tumour is completely frozen
and to minimize injury to the surrounding healthy tissue. However, it is
preferable to use the MR imaging guidance to monitor in real time so that the entire circumference of
the treatment effects can be viewed during the procedure.The MR imaging protocol is limited to the abdomen
and included: transverse T2-weighted, transverse T1-weighted sequences, and
transverse fat-suppressed T1-weighted sequences before and four phases after
the intravenous administration of contrast medium.The purpose of the cryotherapy is
not the excision of the tumor, but their necrosis “in situ.” The effects of
renal cryoabation on the kidney have been studied in animal models [38].The acute
histologic changes are rapid coagulation necrosis and a sharp zone of
transition within the normal kidney. A peripheral zone of incomplete necrosis
surrounds the area of necrosis. Over time, resorption of cellular debris and
fibrosis lead to shrinkage of the cryolesion.Given that the renal lesions are treated “in
situ,” a rigourous followup is required, usually with MR. Data form long-term
followup examinations are crucial to asses the usefulness of cryotherapy and
detecting tumor recurrence.MR imaging and the same protocol
used prior to the treatment are
performed also at 24–48 hours after treatment, for assessment of complications
(bleeding or urinoma).Remer and coworkers [39] reported
several characteristic findings in serial MR scans performed on the first day,
1 month, 3 months, 6 months, and 12 months after renal cryoablation. MR images are
also compared with the pretreatment MR images, to determine the amount of
cryonecrosis, defined as tissue that no longer appeared to be enhanced by
intravenous contrast material.The signal intensities of cryolesions
on T1-and T2-weighted images were somewhat variable. Lesions were generally
isointense on T1-weighted images and iso-or hypointense on T2. The borders of
cryolesions were well depicted on T2-weighted images because of the relative
hypointensity of the lesion compared with normal renal parenchyma.In patients without evidence of tumor recurrence, all cryolesions showed a
dramatic progressive decrease in size over time (63% and 94% at 1 month and 1 year,
resp.). Some cryolesions had a peripheral hypervascularized rim on T1-weighted gadolinium enhanced images. This was seen in up to 50% of lesions
imaged within the first 3 months after ablation, but was present in just 10% of
lesions at 12 months. Initial rim enhancement has been reported in liver
ablation cases and has been attributed to the inflammatory response.Any increase in size of a cryolesion should be viewed with suspicion.Although MR is the most studied
method of monitoring cryolesions, CT has also been evaluated [40]. The cryolesions on followup CT
showed no evidence of enhancement and the tumor demonstrate stable size or
decease in size.



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*Source: 918050-2008-09-25.xml*