The findings of CT and MRI in patients with metanephric adenoma

Abstract

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.

Keywords: Computer tomography; Magnetic resonance imaging; Metanephric adenoma; Pathology.

Fig. 1

A 28-year-old female with metanephric adenoma in the mid and lower poles of the right kidney (case 4). Plain CT showed a round homogeneous isodense mass with a poorly defined margin in the renal medulla. The CT value of the mass was 41 HU (a). Dynamic contrast-enhanced CT revealed a progressive enhancement in the cortex phase (b), parenchymal phase (c), and pelvic phase (d). The CT values of all three phases, respectively, were 51 HU, 58 HU, and 70 HU, lower than that of the normal renal parenchyma. Pathology was assessed with hematein-eosin staining and showed that the morphology of tumor cells was uniform with tubular and acinar architecture (magnification, 40 × 10, e)

Fig. 2

A 43-year-old male with metanephric adenoma in the upper pole of the right kidney (case 3). Plain CT showed a round, poorly defined isodense mass with a little patchy low-density areas in the renal cortex and medulla and the lesion projected outside of the renal contour. The CT value of the mass was 44 HU (a). Dynamic contrast-enhanced CT revealed a slight enhancement of the tumors in the cortex phase with a CT value of 52 HU (b), a further enhancement in the parenchymal phase with a CT value of 57 HU (c), and a slightly decreased enhancement in the pelvic phase with a CT value of 51 HU (d). Pathology was assessed with hematein-eosin staining and showed that the morphology of tumor cells was uniform with tubular and acinar architecture (magnification, 40 × 10, e). The kidney outline has been marked with red line

Fig. 3

A 17-year-old male with metanephric adenoma in the mid and upper poles of the right kidney (case 2). Dynamic contrast-enhanced CT revealed an irregular lesion with a heterogeneous enhancement, multiple patchy calcifications, and cystic changes/necrosis (a). CT angiography revealed the nutrient artery in the lesion (b). Pathology was assessed with hematein-eosin staining and showed that the morphology of tumor cells was uniform with tubular and acinar architecture (magnification, 40 × 10, c). The arrow marker was used to indicate the cystic changes or necrosis

Fig. 4

A 60-year-old male with metanephric adenoma in the lower pole of the right kidney (case 8). T1WI of the tumor showed nearly isointense to renal parenchyma (a). T2 weighted, fat suppressed image showed nearly isointense to renal parenchyma with some slightly hyperintense areas in the center (b). The arrow marker was used to indicate the lesion

Fig. 5

Immunohistochemical images for vimentin, CK and EMA. Immunohistochemical experiments revealed that most tumor cells were positive for vimentin (magnification: 200×, a), CK (magnification: 200×, b) and EMA (magnification: 200×, c)