A classification of reported mesencymal neoplasm is presented in Table I. Although benign mesencymal tumors are more frequently located in renal pelvis, malignant tumors are located in ureter[2].
Table I: Classification of mesenchymal neoplasms of renal pelvıs and ureter
Myxomas are relatively uncommon soft tissue neoplasms. This tumor can be found in various sites in the body including the skin, heart, soft tissue, head and neck. Myxoma of the kidney is extremely rare. To date, eleven cases of pure myxoma reported in the literature (Table II). Only one of them originated in renal pelvis and others were situated in renal parenchyma and capsule. Our case is the second renal myxoma arising in the renal sinus.
Nephrectomy specimen weighed 330 g together with perirenal fat tissue. On sagittal section, the pelvis of the left kidney contained a 9x6x5 cm semitranslucent, gelatinous tumor mass. Tumor involved the renal parenchyma. Other pathologic findings such as calculi, hidronephrosis were not detected on gross examination of the renal tissue (Figure 2). Microscopically, the tumor was composed of hypocellular and hypovascular myxoid stroma. Tumor cells were spindle, fibroblast like, oval and stellate shaped. Nuclear atypia and mitosis were not demonstrated (Figure 3). Tumor was invading renal parenchyma. The tumor and renal parenchyma were indistinct. Ureter was intact. There was no pathological finding in non-tumoral areas. The myxoid stroma was stained with alcian blue and tumor cells were positively stained with vimentin (Figure 4), focally stained positive with smooth muscle actin (SMA), and negatively stained for S100 protein, epithelial membrane antigen (EMA), and pancytokeratin. Final diagnosis was myxoma of the renal sinus according to gross, microscopic and immunohistochemical findings.
Figure 4: Tumor cells positively stained with vimentin (x400).
Myxoma has been described first by Virchow in 1863[4-6]. Although myxomas show similar microscopic appearance, they exhibit different behavioral and clinicopathological course[4-6]. It is suggested that this difference is based on molecular abnormalities[4-6].
Myxomas located in different sites of the body have different molecular mutations and other abnormalities[4-6].
Cells of myxoma considered to be originated from fibroblast like primitive mesencymal cells. These cells are similar to fibroblast but they lost the capacity to polymerize collagen. Some authors believe that myxoma is a myxoid change of some mesenchymal tumors such as leiomyoma and degenerative changes seen in adipose tissue in brown atrophy of the heart[7-9]. The others believe that the uniform cellular component throughout the lesion supports a neoplastic nature rather than a regressive change within the pre-existing tumor[7-9].
Clinicopathological data of the reported twelve cases are shown in Table 2. Data were available in ten of the twelve cases including our case[3,4,7-13]. Six of the patients were male and the age at the diagnosis ranged from 27 to 82 years (mean 51,3). Our case is the most elderly one among these cases. Tumor size varied from 4 to 28 cm (mean 12,2 cm). Tumors were located in lower pole of the kidney in four cases, upper pole in one case, entire kidney in one case and middle pole in three cases except the case reported by Nisimoto K in 1996. Our case is the second one located in renal sinus.
Histopathologic appearance of renal myxomas resembles others located at different sites of the body. The present case showed similar cellular structure with myxoma with the lack of pleomorphism, mitosis and nucleoli.
Renal myxoma should be differentiated from other benign and malignant mesenchymal tumors such as myxoid neurofibroma, myxoid leiomyoma, perineuroma, myxolipoma, myxoid variant malignant fibrous histiocytoma, liposarcoma, leiomyosarcoma and rhabdomyosarcoma. Renal myxoma can be easily distinguished from sarcoma with the lack of anaplastic features in nephrectomy material. Each benign tumor display characteristic histopathological and immunohistochemistry features[8,11,12]. Our case did not have different histological areas such as neural, fibrous, leiomyomatous changes.
The present case was focally stained positive with SMA which reminded leiomyoma possibility in the differential diagnosis. However, specimens which were taken from the tumor did not show any fasciculated spindle cells or bundles that were specific for leiomyoma. Homogeneous structure throughout the sections, focal positive staining with SMA, desmin negativity and loss of parallel alignment of the cells also withdrew us from the diagnosis of leiomyoma[16]. Our case also differed from myxoid liposarcoma with the lack of lipoblastic differentiation and differed from myxoid lipoblastoma with the lack of atypia, characteristic multilobular pattern and existence in the elderly[17,18].
Cytopathological examination can be performed to distinguish benign tumors from malignancies. We have performed fine needle aspiration accompanied with CT before the surgical procedure and the result showed malignancy potential.
In conclusion, we described here a very rare type of mesenchymal tumor of the renal sinus. It is important to distinguish this benign entity from malignant tumors that may exhibit secondary myxoid changes due to overtreatment. The treatment of choice is radical nephrectomy. A case cured with enucleation was also reported in the literature but this was not possible in our case due to infiltration of the surrounding renal parenchyma.
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