Muller Journal of Medical Sciences and Research

: 2013  |  Volume : 4  |  Issue : 1  |  Page : 39--41

Mixed epithelial and stromal tumor of the kidney

Raphael Hart Lyngdoh, Maria Bukelo, Muktha R Pai 
 Department of Pathology, Father Muller Medical College, Mangalore, Karnataka, India

Correspondence Address:
Raphael Hart Lyngdoh
Department of Pathology, Father Muller Medical College, Mangalore, Karnataka


Mixed epithelial and stromal tumor (MEST) of the renal pelvis or the older terminology cystic hamartoma of renal pelvis is a rare benign tumor and recently been recognized as a distinct clinical and pathological entity. These complex neoplasms are composed of a mixture of stromal and epithelial elements and are seen predominantly in women (ratio of women to men 6:1) and are generally seen in perimenopausal women with presenting symptoms of flank pain, hematuria or symptoms of urinary tract infection. We present here a case of MEST in a 48-year-old female who presented with a mass per abdomen associated with a mild dragging pain of 6 months duration. The ultrasonography report was of a multi-cystic lesion in the right kidney. Surgical excision of the lesion showed a mass measuring 18 × 14.5 × 7 cm with attached normal ureter. The outer surface was bosselated and showed multiple-cystic nodules with pale brown to dark brown smooth and glistening surface. The tumor was well circumscribed and there were multiple cysts of varying sizes separated by stroma arising from the dilated pelvicalyceal system. The wall of the cysts are covered by papillary excrescences. On histological examination, a well delineated tumor composed of cysts of varying sizes lined by columnar, cuboidal and transitional epithelium. Surrounding stroma showed a mixture of ovarian type of stroma and spindle shaped cells of smooth muscle type having plump nuclei. Sections from the renal-tissue adjacent to the tumor showed normal glomeruli and tubules.

How to cite this article:
Lyngdoh RH, Bukelo M, Pai MR. Mixed epithelial and stromal tumor of the kidney.Muller J Med Sci Res 2013;4:39-41

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Lyngdoh RH, Bukelo M, Pai MR. Mixed epithelial and stromal tumor of the kidney. Muller J Med Sci Res [serial online] 2013 [cited 2022 Jul 5 ];4:39-41
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Full Text


Mixed epithelial and stromal tumor (MEST) of the kidney is a recently recognized distinct neoplasm. The literature survey showed few case reports of this lesion but with various terminologies viz., cystic hamartoma of the renal pelvis, MEST, and adult mesoblastic nephroma. [1],[2],[3],[4],[5] The varying terminologies used and its rare occurrence has made it difficult to assess accurately the true incidence and hitherto the largest series being of 34 cases collected from five large academic institutions. [6] Nevertheless, this tumor with heterogenous stromal and epithelial morphology should be distinguished from other cystic benign and malignant renal neoplasms. MEST of the kidney occurred exclusively in women aged 36-80 years, majority of whom had a history of estrogen therapy and/or obesity. [3] MEST are relatively rare as review of the literature showed only isolated case reports and small case series. [7] Here, we present this unusual tumor of the kidney in a perimenopausal woman which occurred as an incidental renal mass.

 Case Report

A 48-year-old female presented to the surgical out-patient department with a mass per abdomen and associated with mild dragging pain for 6 months. On abdominal examination, the mass was felt in the right lumbar region extending to the right hypochondrium, right iliac fossa and was crossing the midline near the umbilicus. It was bimanually palpable. She did not have any history of estrogen therapy. The ultrasonogram report was of a multi-cystic mass of the right kidney measuring 18 × 14 × 10 cm. The mass contained irregular small cystic pockets. Her routine blood examination for complete blood count, blood sugar level and electrolytes were within normal limits. Her blood urea level was however increased at 83 mg/dl. Her plain X-ray chest was normal. Based on ultrasonographic finding of an enhancing, multi-cystic renal mass with a differential diagnosis of (a) multi-loculated cystic tumor (b) cystic renal cell carcinoma and (c) multi-loculated cystic nephroma, right nephrectomy with the mass was carried out. Gross examination of nephrectomy specimen revealed a large cystic mass measuring 18 × 14.5 × 7 cm which projected into the renal pelvis but was confined within renal capsule. There was attached ureter measuring 20 cm in length. The outer surface was bosselated and showed multiple cystic to solid nodules with pale brown to dark brown smooth and glistening surface [Figure 1]. There were multiple cysts of varying sizes arising from the dilated pelvicalyceal system, the cysts contained smaller cyst pockets [Figure 2] with fluid and the inner surface was covered by papillary excrescences [Figure 3]. On histological examination, a well demarcated tumor composed of micro-cysts of varying sizes lined by mixture of columnar, cuboidal to transitional epithelium with focal small papillary tufts [Figure 4]. The architecture of the micro-cysts varied from simple micro-cysts with abundant stroma between them to densely packed clusters of micro-cysts [Figure 5]. Dilated complex branching channels were also seen. The stroma consisted of variable population of spindle cells with plump nuclei and abundant cytoplasm. Compressed epithelial tubules were surrounded by smooth muscle fibers and ovarian tissue like stroma [Figure 6]. Sections from the renal tissue adjacent to the tumor showed normal mature glomeruli and tubules.{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}


Cystic neoplasms of the kidney in the adult age group are uncommon and consist mostly of cystic variants of renal cell carcinoma. MEST is a distinctive benign neoplasm classically comprising of both mesenchymal and epithelial elements. These tumors have been published using various types of nomenclature in medical literature such as leiomyomatous renal hamartoma, adult mesoblastic nephroma, and cystic hamartoma of renal pelvis. [1],[2],[3],[4],[5],[7]

The term MEST was first introduced by Michal and Syrucek [7] in 1998 to describe a biphasic cystic lesion with grossly recognizable stroma in a middle aged woman. MEST was reported as a rare entity by Mensch et al. [1] and Yoshida et al. [2] whereby, they described a biphasic proliferation of epithelial and mesenchymal elements along with presence of adipocytes. The stroma consisted of smooth muscle, which reacted positively to antibodies against alpha-smooth muscle actin, desmin, and vimentin. They concluded that this entity is distinct from other renal tumors such as mesoblastic nephroma, cystic nephroma or a cystic partially differentiated nephroblastoma. This benign neoplasm lacked nephrogenic rests or blastemal cells that are seen in nephroblastoma. Mesoblastic nephroma has similar spindle cell stroma but is seen in children and lacks epithelial elements [1],[2] whereas cystic nephroma has low stromal to epithelial ratio with large cysts and thin fibrous septa. In the present case the tumor showed varying proportion of epithelial tissue in the form of epithelial tubules and stroma was heterogenous. The cysts were characteristically lined by cuboidal to columnar epithelium at places forming micropapillary tufts as described by Eble et al. [8] The tumor focally showed hypercellular ovarian type stroma and smooth muscle fibers. Surrounding renal tissue showed mature glomeruli and tubules. These stromal features strongly target the diagnosis of MEST. The peculiar stroma in these tumors provides embryologic clue regarding origin of these tumors. One possibility is the presence of fetal primitive mesenchyme in the kidney and other possibility is the proximity of the primitive gonads to the urogenital ridges, which may cause incorporation of ovarian stromal cells into the ureteric bud and metanephric mesoderm. In situations of hormonal stimulation or imbalance, these cells become active and secrete paracrine factors to induce proliferation of adjacent epithelium. [6] All reported cases of MEST have behaved in a benign fashion following surgical excision. However, one case recurred locally 21 years after excision. [4]

In conclusion, MEST is a relatively rare and distinct benign neoplasm of the kidney that should be distinguished from other cystic neoplasms.


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