Metanephric Adenoma: clinical, imaging, and Histological findings

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.

Renal Tumors of Childhood: Radiologic-Pathologic Correlation Part 2. The 2nd Decade: From the Radiologic Pathology Archives

Malignant renal tumors account for 7% of childhood cancers, and Wilms tumors are by far the most common-but not in older children and adolescents. Among individuals in the latter half of their 2nd decade of life, renal cell carcinoma (RCC) is more common than Wilms tumor. The histopathologic spectrum of RCCs in children differs from that in adults. The most common subtype of RCC in children and adolescents is Xp11.2 translocation RCC, which is distinguished by hyperattenuation at nonenhanced computed tomography, a defined capsule, and associated retroperitoneal lymphadenopathy. Papillary RCC is the second most common histologic subtype. It enhances less intensely compared with the adjacent renal parenchyma and has a propensity for calcification. Clear cell RCC is seen in patients with von Hippel-Lindau disease and is distinguished by its relatively hypervascular nature. Medullary carcinoma affects adolescents with the sickle cell trait and is characterized by an infiltrative growth pattern and extensive metastasis at presentation. Angiomyolipoma is seen in children with tuberous sclerosis complex and is often multifocal and hypervascular, with macroscopic fat. Metanephric tumors are central, circumscribed, and typically calcified. Lymphoma usually manifests as multifocal masses, but it may involve a solitary mass or infiltrative pattern. Extensive adenopathy and involvement of the gastrointestinal tract or other organs also may be seen. Primitive neuroectodermal tumor is an aggressive neoplasm that is typically quite large at diagnosis. Knowledge of the clinical, biologic, and histopathologic features of renal tumors in older children and adolescents and their effects on the imaging appearance can help the radiologist offer a useful preoperative differential diagnosis.

Retroperitoneal laparoscopic partial nephrectomy for treatment of metanephric adenoma (Report of 6 cases)

Objectives

To investigate the clinical and pathological features of metanephric adenoma (MA) and the clinical outcome after retroperitoneal laparoscopic nephron-sparing surgery.

Methods

Six out of 183 partial nephrectomies performed during January 2009 to August 2014 were confirmed to be MA confirmed by postoperative pathological study. Perioperative parameters of the six patients were then retrospectively collected, analyzed and compared with current literature, including warm ischemia time (WIT), total operation time, estimated blood loss (EBL), positive surgical margin (PSM), and complications. Surgical and oncological outcome of all six patients were evaluated based on a mean follow up of 17 months (5–48 months).

Results

Tumors in all six cases were all successfully removed by partial nephrectomy. Mean WIT was 24.7 min (19–35 min). Mean operation time was 103.6 min (82–147 min). Mean EBL was 53.5 ml (20–85 ml). No conversion, transfusion or other major complication were observed in all six cases. Postoperative pathology confirmed negative surgical margin in all six cases. During a mean of 17 month follow up (5–48 months), no local recurrence or metastasis were found in all six cases.

Conclusion

MA is a rare benign primary kidney epithelial cancer, which could hardly be differentiated from renal malignancies based on preoperative imaging. Our data suggested that retroperitoneal laparoscopic partial nephrectomy can be used for surgical treatment of MA, in terms of tumor control and preservation of renal function.

Adult metanephric adenoma presumed to be all benign? A clinical perspective

Background

In most documented literature, metanephric adenoma (MA) is described as a benign tumour. Nevertheless, the nature of MA remains unclear and the clinical criteria of different MA subtypes are not well established. In the present study, we investigated the clinicopathological characteristics of MA, especially those of the uncommon histological subtypes.

Methods

A cohort study was performed on 18 patients with pathologically proven MA in our institute from January 2004 to June 2014. The patients’ clinicopathological and radiological data were retrospectively analysed and evaluated with an emphasis on the corresponding subtypes.

Results

The patient population had a female: male ratio of 1:1 and mean age of 50 years (range, 18–66 years). The mean tumour size was 3.9 cm (range, 1.4–9.0 cm). There were no pathognomonic radiological features that posed a challenge for a preoperative diagnosis of MA. Fourteen patients underwent radical nephrectomy, and the other four underwent partial nephrectomy. Three histological subtypes were observed: classic MA (n = 10), malignant MA (n = 2), and composite MA with coexistence of different malignant components (n = 6). Despite the presence of atypical histological features and malignant components among the patients, only one patient developed distant metastasis (median postoperative follow-up, 56 months; range, 30–86 months).

Conclusions

MAs are a heterogeneous group of neoplasms with different biological characteristics. The correct identification of this entity and its subtypes would facilitate stratification of optimal management protocols and accurate assessment of the prognosis.

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.

Fine-needle aspiration of metanephric adenoma of the kidney with clinical, radiographic and histopathologic correlation: a review

Metanephric adenoma of the kidney is an uncommon benign epithelial neoplasm with only a small number of reports that describe its cytologic features. We describe two additional cases of metanephric adenoma diagnosed on fine-needle aspiration biopsy and review the available literature. Our cases showed similar cytology and were composed of cellular smears with numerous clusters of small, oval to round cells arranged in a microfollicular pattern and papillary configurations. The tumor cells had scant cytoplasm, fine chromatin and absent nucleoli. Psamomma bodies, nuclear atypia, cellular cpleomorphism, necrosis, and mitoses were absent. Because of the rarity of this tumor and the common cytologic features it shares with other lesions, including malignant tumors such as Wilms' tumor and papillary renal cell carcinoma, awareness of the cytologic features of metanephric adenoma may aid in avoiding a diagnosis of malignancy, especially preoperatively, and in guiding the proper management for the patients.

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.