CT and ultrasound findings of metanephric adenoma: a report of two cases and literature review

Case Report: MRI, CEUS, and CT Imaging Features of Metanephric Adenoma with Histopathological Correlation and Literature Review

The metanephric adenoma is an extremely rare, benign, embryonal-epithelial neoplasm of the kidney and has a good prognosis with appropriate treatment. It can present at any age and is often asymptomatic. Histologically, the lesion is well established; however, there have been only a few cases described with available detailed imaging findings, most of them with large renal masses typically depicted by computed tomography (CT). This case report includes imaging of contrast-enhanced MRI, contrast-enhanced ultrasound (CEUS), and CT, and thus adds to the information available, potentially promoting a nephron-sparing clinical pathway. We report on the clinical presentation, imaging, histopathological diagnosis, and treatment data of a 27-year-old female, in whom an incidental, symptomatic kidney tumor was detected. CT, CEUS, and MRI showed a suspicious unifocal renal lesion with inhomogeneous enhancement, which was indistinguishable from renal cell carcinoma. After laparoscopic resection, a metanephric adenoma with microscopically partially glandular, partially nest-like solid growth and without distinctive atypia was diagnosed pathohistologically. Immunohistochemistry results were positive for Wilms Tumor 1 and CD57 and negative for EMA and CK7: 2–3% positive cells in MIB1 coloring. At 3-month and 1-year follow-up, the patient was asymptomatic and imaging showed no recurrence of renal masses or metastases.

Paediatric metanephric tumours: a clinicopathological and molecular characterisation

To characterize metanephric tumours in children, we performed a literature review investigating paediatric metanephric adenomas (MA), metanephric stromal tumours (MST) and metanephric adenofibromas (MAF). Including two patients from our own institution (MA, MAF), 110 individual cases (41 MA, 20 MAF, 49 MST) were identified. Additionally, fifteen composite tumours were identified, with areas of MA/MAF and Wilms tumour (WT) or papillary carcinoma. No distinct clinical or radiological features could be defined. In pure metanephric tumours, histologically proven distant metastases were reported once (MA), relapse was reported once (MST) and one tumour-related death occurred (MST). Somatic BRAF-V600E mutations were tested in 15 cases, and identified in 3/6 MA, 3/3 MAF, and 6/6 MST. In our institution the MA harboured a somatic KRAS-G12R mutation. Overall, paediatric metanephric tumours are difficult to discriminate from other renal tumours at presentation, behave relatively benign, and the occurrence of composite tumours warrants analysis of underlying (genetic) pathways.

Imaging features of metanephric adenoma and their pathological correlation

AIM

To analyse the imaging features of metanephric adenoma (MA) and their pathological correlation.

MATERIALS AND METHODS

The imaging findings in 11 patients with MA were studied retrospectively. Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) findings were studied in seven, 11, and six patients, respectively. The enhancement pattern, attenuation, lesion location, size, cystic or solid appearance, capsule sign, and presence of calcifications were evaluated.

RESULTS

On ultrasonography, MA presented as hypoechoic (4/7), slightly hyperechoic (1/7), isoechoic (2/7), and with a clear boundary. Unenhanced CT showed unclear boundaries (11/11), homogeneous isodensity (8/11), with calcification (1/11), necrosis (1/11), and heterogeneous hyperattenuation (1/11). Mean CT attenuation values on unenhanced and enhanced CT (cortical phase, corticomedullary phase, and excretory phase) were 38.87±6.66, 55.71±17.74, 67.77±16.86, and 65.62±15.99 HU, respectively. The degree of enhancement of the lesions in each phase was statistically significantly lower than that of the surrounding normal renal parenchyma (p=0.00). The pattern of enhancement of the solid component was slight and gradual enhancement (9/11). The tumour was located entirely within the renal medulla in nine cases, and two cases demonstrated an exophytic pattern. All tumours showed a clear boundary on enhanced CT, but capsules were not found. The mean greatest tumour diameter was 3.5 cm. MA showed markedly hyperintense on the diffusion-weighted MRI sequence (DWI) and delayed enhancement of the tumour capsule on enhanced MRI.

CONCLUSIONS

Imaging features of MA are usually solid and hypovascular, and show prolonged, and homogeneous mild enhancement that is less than that of the surrounding normal renal parenchyma in all phases. MA is markedly hyperintense on DWI.

Metanephric adenoma with low apparent diffusion coefficient value mimicking renal cell carcinoma: A case report

RATIONALE

Metanephric adenoma (MA) is a rare and often benign tumor. Most MAs were misdiagnosed as renal cell carcinomas (RCCs) preoperatively. Diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping can help to differentiate benign and malignant tumors. However, there are still pitfalls in using DWI and ADC to discriminate benign and malignant lesions.

PATIENT CONCERNS

A 56-year-old woman had a right renal metanephric adenoma. The tumor showed very low ADC value preoperatively and was misdiagnosed as a renal cell carcinoma.

DIAGNOSIS

Intraoperative ultrasound-guided percutaneous biopsy of tumor was performed. Based on the histopathological findings and immunohistochemical stains, a diagnosis of metanephric adenoma was suggested.

INTERVENTIONS

The patient received percutaneous cryoablation of this tumor. Five years later, she underwent right partial nephrectomy because local recurrence was revealed on a follow-up computed tomography (CT).

OUTCOMES

MA was confirmed again by histological examination. The patient was uneventful after surgery.

LESSONS

ADC mapping can be used for differentiating RCCs from other benign tumors by their lower ADC values. However, some benign and malignant lesions have overlapped low ADC values. This case illustrated that a benign lesion such as MA could mimic RCC on ADC, by its highly cellular component. Cryoablation is an optional treatment, which has an increased risk of local recurrence. Follow-up CT or MRI is useful and necessary for detection of local recurrence by depicting enhancing solid parts in a tumor over time.

The findings of CT and MRI in patients with metanephric adenoma

Background

Metanephric adenoma (MA) is a benign renal tumor that is difficult to distinguish from a malignant tumor via traditional radiography. The diagnosis of MA is often dependent on postsurgical histopathological examination. In the present report, the imaging features of MA on computer tomography (CT) and magnetic resonance imaging (MRI) were retrospectively evaluated.

Methods

Eight MA patients, 17–67 years of age, were pathologically confirmed and recruited between April 2009 and November 2014. Four of the eight patients were female. All patients underwent CT scanning, and one patient underwent MRI scanning. Three patients underwent CTA of the renal arteries. All patients underwent resection surgery (radical nephrectomy in five and nephron-sparing surgery in three patients).

Results

The average tumor size was 44.0 ± 23.6 mm. The lesions in 87.5 % cases were located both in the renal cortex and medulla and exhibited exophytic growth. Plain CT showed that MA tumors were solid, and the average CT value was 37.9 ± 6.7 HU. Dynamic contrast-enhanced CT revealed that enhanced degrees of MA tumors in the renal cortex, renal parenchymal, and pelvic phase were all lower than that of normal renal parenchyma. A slight enhancement in the renal cortex phase and an even higher enhancement in the renal parenchymal phase were observed in seven of the cases. Progressive enhancement in the pelvic phase was found in five cases and a slight decreased enhancement in the pelvic phase in two cases. MRI revealed that MA tumor was isointense on T1WI and isointense on T2WI with some slightly hyperintense areas in the center. CTA of the renal arteries revealed the nutrient artery in one patient and no nutrient artery in two. Immunohistochemical experiments demonstrated that most tumor cells were positive for vimentin, CK, and EMA.

Conclusions

MA is a rare benign renal neoplasm. Detailed knowledge of the CT and MRI characteristics of MA plays an important role in MA diagnosis and treatment.

A Case of Metanephric Adenoma and Acute Myocardial Infarction

Metanephric adenoma (MA) is a rare neoplasm that acounts for 0.2% of adult renal neoplasms. MAs are typically discover incidentally during detailed examinations for nonspecific symptoms such as abdominal or flank pain, hematuria, fever and palpable abdominal mass. Additionally, polycythemia has occasionally been reported as well. Herein we describe a case of metanephric adenoma which was an incidental finding in the course of a clinical autopsy in a patient with complete AV block and polycythemia. Histologically, the tumor was composed of small and uniform tubular structures reminiscent of renal tubuli, without signs of cellular atypia and pleomorphism. Such tumor histomorphology was consistent with the diagnosis of metanephric adenoma. Thrombosis is a common complication of polycythemia that often causes death. Polycythemia with an increasing number of blood cells causes hyperviscosity and, in 20-40% of cases, lethal thrombosis or hemorrhage. Hyperviscosity and coronary artery disease in our patient caused acute myocardial infarction with the subsequent rupture of posterior left ventricle wall and hemopericardium.

Cytologic features of metanephric adenoma of the kidney: case report and review of the literature

Metanephric adenoma (MA) is a rare, benign renal tumor that can be found in individuals of any age. The histological features of this lesion are well known; however, cytological features of this entity have rarely been described. Herein, we present the case of a 37-year-old white woman with multiple endocrine dysfunctions and a renal mass. The diagnosis of metanephric adenoma was suggested as a differential diagnosis during imprint cytology; this diagnosis was later confirmed by core needle biopsy (CNB) and the results of immunostaining. To our knowledge, this is the first time in the literature that the diagnosis of metanephric adenoma was initially suggested on imprint cytologic testing of a CNB. We review the literature regarding the cytologic features and immunohistochemical reactivity of this tumor to raise awareness of this entity among pathologists and to distinguish it from other lesions, such as renal-cell carcinoma, so physicians can use this information to help them avoid calling for an unnecessary radical nephrectomy.

CT imaging spectrum and the histopathological features of adult metanephric adenoma

OBJECTIVE

To retrospectively evaluate the radiopathological features of adult metanephric adenoma (MA) and explore whether MA can be differentiated on CT images, including the basis of their morphological features and enhancement patterns.

METHODS

18 consecutive MA cases (age range, 18-66 years; 9 males and 9 females) were pathologically proven and recruited in our study between January 2004 and June 2014. Unenhanced and contrast-enhanced CT were performed and correlated with corresponding pathological findings to differentiate between MA and other renal tumours. The enhancement pattern, lesion contour and presence of calcifications were evaluated.

RESULTS

On unenhanced CT scan, the most common (n = 15, 83.3%) CT imaging characteristics were the presence of homogeneity and well-defined solid renal masses; the minority (n = 3, 16.7%) were heterogeneous or centrally located low-attenuation masses. Contrast-enhanced CT image revealed hypoattenuating heterogeneous masses with varying degrees of contrast enhancement in 16 (88.9%) cases, in contrast to those without increased attenuation in 2 (11.1%) cases. Scattered calcification was found only in one case (5.6%). Pathological results revealed that a total of 6 (33.3%) cases had concomitant malignant carcinoma components; 2 (11.1%) patients had malignant MA; and pure MA was found in 10 cases, with a surprisingly high proportion of malignant tumours.

CONCLUSION

The positive-predictive values of "high" enhancement seemed relatively characteristic for the diagnosis of malignant and composite MA.

ADVANCES IN KNOWLEDGE

Radiopathological features of adult MA and exploring whether MA can be differentiated on CT images, including the basis of their morphological features and enhancement patterns.

The imaging features of metanephric adenoma: a case report and review of literature

Metanephric adenoma (MA) is a rare epithelial tumor of the kidney with a characteristic histology. To date, the imaging features of the tumor have not been clearly described. Until now, MA was considered to be benign, but the majority of MA cases underwent nephrectomy. Here, we report a case of MA confirmed by surgical pathology, and we will analyze the ultrasound and computed tomography findings. The radiological features of MA are presented along with a brief review of the pertinent literature to deepen the understanding of MA’s imaging features.

Renal metanephric adenoma mimicking papillary renal cell carcinoma on computed tomography: a case report

We present a case of renal metanephric adenoma (MA) mimicking papillary renal cell carcinoma (PRCC) on computed tomography (CT). In the present case, double-phase enhanced CT showed a hypovascular right renal tumor with gradual and prolonged enhancement. The renal tumor was surgically removed. Histological examination of the resected specimen showed renal MA. Although the radiological features of renal MA have been described by some authors, only a few reports have mentioned the pattern of enhancement on multiphase enhanced CT. The pattern of enhancement of a renal tumor is likely to be correlated with its pathological features. Since renal MA is thought to be genetically related to PRCC, these two tumors are likely to demonstrate similar radiological features, so that differentiating between them becomes difficult. In patients with a hypovascular renal mass that shows gradual and prolonged enhancement on multiphase enhanced CT, the diagnosis of renal MA should be considered.

Beyond renal cell carcinoma: rare and unusual renal masses

The vast majority of primary renal masses represent clear cell or papillary renal cell carcinomas, angiomyolipomas, or transitional cell carcinomas. However, a number of more rare masses can also be encountered, many of which can be very difficult to differentiate from these more common entities based on their imaging features. These uncommon entities include metanephric adenoma, epithelioid angiomyolipoma, medullary renal cell carcinomas, multilocular cystic nephroma, hemangiopericytoma, hemangioma, leiomyoma, leiomyosarcoma, solitary fibrous tumor, renal plasmacytomas, and mixed epithelial and stromal tumors. In some cases, certain clinical and imaging features can allow one of these unusual entities to be placed in the differential diagnosis, including patient age, degree of tumor enhancement, presence of underlying sickle cell trait or sickle cell disease, the presence of a cystic component to the tumor, and tumor morphology. Even if a radiologist is unable to make a specific diagnosis, knowledge of these entities is important, as it allows radiologists to guide post-surgical follow-up, as well to understand the most common sites of metastatic disease.