Renal myxoma : a case report Mixoma renal : relato de caso

Myxomas are rare tumors that can appear in many anatomical locations. There are only 14 cases of renal involvement documented in the literature. This article reports a case of renal myxoma in an elderly woman with recurrent cystitis. After five years of follow-up, the computed tomography (CT) revealed a large solid tumor mass in the left kidney. Tumor resection was performed preserving the affected kidney with histopathological diagnosis of renal myxoma. The objective of this study is to report a rare case of renal myxoma, emphasizing the importance of the differential diagnosis from other benign and malignant mesenchymal tumors.


CaSE REPoRt
The patient was a white woman, aged 73 years, showing recurrent cystitis since 2003.In 2005, after new bouts of cystitis, an ultrasonography (US) was performed and bilateral renal cysts were detected, they were 4.2 cm in the left kidney and 1.4 cm in the right kidney.In 2007, she complained of right-sided cramplike lumbar pain, irradiating anteriorly, with nausea, negative renal fist percussion, and right-sided flank pain at palpation.Computed tomography (CT) was ordered, and showed kidneys with reduced volume, lobulated contour, preserved parenchymal thickness, bilateral renal cortical with rounded and hypodenses formations, (cysts) without significant enhance after contrast medium, measuring 7.4 × 6.8 cm in the middle third of the left kidney (Figure 1).After six months, the control CT scanning showed, besides the cortical cysts, the presence of a solid tumor mass, enhanced by contrast medium, measuring 11.9 × 10.1 cm, with well-defined edges in the left flank, suggesting neoplasia (Figure 2).There were no other changes in biochemical and urinalysis tests.
The patient underwent partial nephrectomy due to the exophytic tumor found with gelatinous and well-defined aspect, with narrow pedicle, without lymphadenopathy.The histopathologic diagnosis was myxoma.It showed short spindle-shaped cells with small, oval, delicate nuclei, without hyperchromasia or mitotic activity.Cytoplasm was reticular diffuse and eosinophilic.The cells were involved in a myxoid stroma highly vascularized.Immunohistochemistry showed unique positive tumor cells for vimentin.However, the de S-100 protein, smooth muscle actin, cytokeratin, and murine double minute 2 (MDM2) expression were negative (Figures 3 and 4).

DiSCuSSion
It was Virchow (17) who first introduced the term myxoma, and Stout (18) established that the myxoma is a tumor composed of stellate or spindle-shaped cells, with myxoid stroma containing mucopolysaccharide, through which delicate reticular fibers run in various directions.We also examined and determined criteria for distinguishing myxomas from sarcoma variations and mesenchymal neoplasms.
Currently, there is no records of specific clinical presentation for renal myxoma (16) and, due to its rarity, renal myxoma is often confused with other malignant lesions (16) .It is known so far that there is no invasion, metastasis or recurrence (8) .In our renal myxoma case, the patient had concomitant kidney cysts, and in a recent article published, there was also, hemorrhagic cysts concomitant with myxoma (16) .Its differential diagnosis includes a variety of benign and malignant mesenchymal tumors that may show occasionally prominent myxoid features (2) , namely: perineurioma, myxoid neurofibroma, myxoid leiomyoma, myxolipoma and myxoid variant of malignant fibrous histiocytoma, leiomyosarcoma (19) , rhabdomyosarcoma and extraskeletal chondrosarcoma (3,7,8) , low-grade fibromyxoid sarcoma (20,21) , and solitary fibrous tumor (22) .There is still no description of renal myxomas in the literature (3) .
Macroscopically and microscopically, renal myxomas resemble the primitive mesenchyme.The tumor may be found in different locations in the body, the most common is intramuscular (2,3) .It is believed that it is originated in fibroblasts that have lost the ability to polymerize collagen (3) , however, there are controversies in the literature (2,10,15) .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 (2,10,15) .Macroscopically, the tumor has gelatinous aspect and is welldefined (8) .Histopathologically, it is composed of thin fibroblastslike spindle-shaped cells, scattered in an abundant myxoid stroma, closely resembling primitive mesenchyme and myxomas of other sites in the body (3) .It is considered a benign fibroblastic tumor because mitotic activity and cell pleomorphism are not present (8) .
In a wide literature review in 1994, Melamed et al. assert that only five case reports were truly renal myxomas, including their two cases.The remaining cases exhibit features of sarcoma, fibroepithelial, polyp or myxolipoma (2) .
The imaging exams demonstrate the renal myxoma as a large heterogeneous mass, predominantly hyperechoic on US and hypodense on CT scan, with more homogeneous signal on magnetic resonance imaging (MRI), which presents with low signal intensity on T1 and hyperintense on T2.Its contours are relatively regular, discreetly multilobulated, and its interface is well-defined with the adjacent renal parenchyma, only shifting the structures without invading them (23) .
Radical nephrectomy is considered the treatment of choice, showing no recurrence or metastasis in any case (8) .In one case only tumor enucleation was performed (24) .Our case is the second in which there was kidney preservation, and the second that had renal cysts.As it is a benign tumor, we agree that, under the guidance of imaging examination, percutaneous biopsy may be a better option in the future for renal preservation, enabling better operational planning with maximum preservation of the affected kidney (16) .
The patient is currently being monitored, free of recurrence and metastasis.
In conclusion, renal myxoma is a rare tumor with good prognosis and has its origin in fibroblasts (3) .The differential diagnosis is important to avoid confusing it with a variety of malignant and benign mesenchymal tumors such as sarcomatoid carcinoma, which may show secondary myxoid features (2) .The best treatment option would be, when conditions are favorable, tumor enucleation with the preservation of the affected kidney.

figuRE 1 −
figuRE 1 − Kidneys normally located, reduced volume, lobulated contour, cortical parenchymal thickness preserved with rounded and hypodenses formations without significant enhancement after contrast medium, measuring 7.4 × 6.8 cm the largest cm in the middle third of the left kidney