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May 2023, Volume 73, Issue 5

Case Reports

Mixed epithelial and stromal tumour of the kidney masquerading as hydatid cyst: a rare case report from the developing world

Naveed Ahmed Mahar  ( Department of Urology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan. )
Mushtaq Hussain  ( Department of Urology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan. )
Syed Arslan Shehzad Shah  ( Department of Urology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan. )
Harris Hassan Qureshi  ( Department of Urology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan. )
Sara Rasheed Kalwar  ( Department of Urology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan. )
Gauhar Sultan  ( Department of Urology, Sindh Institute of Urology and Transplantation (SIUT), Karachi, Pakistan. )


Mixed epithelial and stromal tumour (MEST) is a rare entity with an incidence of 0.2% among renal cancers. It has strong predilection towards females with a 1:6 male to female ratio, the tumour is cystic with some solid component with biphasic proliferation of stromal and epithelial cells.

The case of a 37-years-old female is presented with right lumbar pain since 3 months. The family history was unremarkable. The routine workup revealed mild neutrophilia and borderline Echinococcus antibody titres. Ultrasound revealed a complex cystic lesion with a solid component in the right kidney. CT scan with contrast confirmed a multiloculated mixed density lesion with daughter cysts arising from the middle lobe of the right kidney. Initial diagnosis of renal hydatid cyst was established and she underwent partial nephrectomy with excision of the cystic mass. Surprisingly the histopathology revealed mixed epithelial and stromal tumour.


Keywords: Hydatid cyst, Mixed epithelial and stromal tumor, Echinococcus, Partial nephrectomy.


DOI: 10.47391/JPMA.6876


Submission completion date: 26-05-2022

Acceptance date: 13-10-2022




Mixed epithelial and stromal tumour of the kidney (MEST) is a very rare entity with a prevalence of 0.2% of all renal tumours. It usually occurs in females with the ratio being 1:6 male to female1. The tumour is composed of stromal cells with an epithelial component2. Mostly it is an incidental finding but sometimes patients may present with a flank mass, pain, and haematuria. Although not pathognomonic, but common radiological finding is a solid and cystic mass3. We report a case of MESTK mimicking hydatid cyst disease of the kidney which was treated by nephron sparing surgery.


Case History


A 37 year old female with no known comorbids presented to the uro-oncology clinic of Sindh Institute of Urology and Transplantation, Karachi in June 2021 with right lumbar pain since 3 months. There were no other associated symptoms like fever or haematuria. Her family history and physical examination was unremarkable. Routine laboratory investigations were performed. The complete haemogram revealed mild neutrophilia whereas the liver and renal function tests were normal. The immunological examination showed borderline positive Echinococcus antibody titres, with no evidence of hydatiduria. Ultrasound scan of the abdomen and pelvis revealed a complex cystic lesion arising from mid- pole of the right kidney with solid component and minimal internal vascularity. Rest of the viscera were unremarkable. (Figure1)



CT Scan of the abdomen with contrast revealed normal left kidney with the right kidney showing a mixed density cystic lesion involving the midpole with contrast enhancement.

A selected coronal section image of the right kidney showed a mixed density mass arising from the mid-pole extending into the upper pole with endophytic as well as exophytic component (Figure-2 a). The selected axial section image demonstrated a contrast enhancing mixed density mass with multiple cysts (Figure-2 b).



Nephron sparing surgery was performed via the lumbar approach. The right kidney was mobilised to take arterial control (Figure-3 a). A large multilocular cystic lesion arising from the middle portion of the kidney in front of the hilum extending from upper pole to lower pole was identified (Figure-3 b and c). Right partial Nephrectomy including excision of the cystic mass was done after inserting a double J (DJ) stent (Figure -3 d). The specimen was sent for histopathology. The patient was kept on Albendazole to decrease the risk of recurrence. The post-operative recovery was unremarkable.



The gross histopathology findings were a single encapsulated, multicystic specimen with an attached kidney parenchyma measuring 13x10x4 cm. Multiple cysts were seen on the cut surface. No hard areas were identified and the surgical resection margins were unremarkable.

The microscopic examination in the low-power view showed normal kidney parenchyma on right side and a well-circumscribed biphasic lesion composed of cystic dilated tubules embedded in spindle cell stroma, on the left side of the field. (HE, ×50). (b): The low-power view projected areas of broad papillary fronds covering the stromal cores with foci of lipometaplasia in the stromal component. (HE, ×100). (c): Medium-power view showed papillary fronds lined by monolayered cuboidal epithelium and comprising of spindly stroma. (HE, ×200). (d): High-power view revealed papillary fronds with focal nuclear hobnailing. No cytologic atypia or necrosis was seen. (HE, ×400).Figure 4-a



At 6 months follow up the patient remained asymptomatic with no evidence of recurrence on imaging and laboratory parameters.




Mixed epithelial and stromal tumor is a rare cystic come solid renal mass. Pawade et al4 described it as a cystic hamartoma of the renal pelvis. Michal and Struck nominated it “mixed epithelial and stromal tumour” of the kidney5, generally considered as a benign condition with strong predilection for perimenopausal women receiving estrogen replacement therapy. However some cases have been reported in, male and paediatric patients6. Microscopically, the tumour is biphasic, with both epithelial and stromal cell elements with expression of estrogen and progesterone receptors7. Turbiner et al. confirmed 62% and 85% of estrogen and progesterone receptor expression respectively8. Wang et al9 denied association of hormone replacement therapy and MEST in a series of 8 cases. There are no specific diagnostic clinical or radiological features attributed to MEST. On a CT scan, it mimic multilocular cystic renal cell carcinoma due to manifestation of mixed density tumor with contrast enhancement10. Immunohistochemically, the epithelial components show positivity for epithelial membrane antigen and cytokeratin. Spindle cells are usually diffusely strong positive for desmin, actin and vimentin10. Our patient had no history of estrogen therapy. There is reported evidence of malignant transformation in few cases of MEST3. Malignant features can occur in either component of the tumor10. In our patient, we did not see features of malignant transformation. The tumour should be distinguished from other cystic neoplasms. Radical nephrectomy or nephron-sparing surgery should be performed where indicated. Routine surveillance and follow-up is advised owing to the risk of malignant transformation and recurrence. There are some limitations to accurate diagnosis as we lack single diagnostic investigation or imaging.




Mixed Epithelial and Stromal Tumour is a rare renal neoplasm that can mimic infective process, it warrants strong susceptibility index and vigilance for correct diagnosis and prompt adequate management.


Patients Consent: Patient’s written consent was taken to publish this case report


Disclaimer: None.


Conflict of Interest: The person who signed ethical review statement is also a co-author of the same manuscript.


Source of Funding: None.




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2       Lane BR, Campbell SC, Remer EM, Fergany AF, Williams SB, Novick AC, et al. Adult cystic nephroma and mixed epithelial and stromal tumor of the kidney: clinical, radiographic, and pathologic characteristics. Urology. 2008; 71:1142-8. doi: 10.1016/j.urology.2007.11.106.

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4       Pawade J, Soosay GN, Delprado W, Parkinson MC, Rode J. Cystic hamartoma of the renal pelvis. Am J Surg Pathol. 1993; 17:1169-75. doi: 10.1097/00000478-199311000-00010.

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7       Choy B, Gordetsky J, Varghese M, Lloyd GL, Wu G, Miyamoto H. Mixed epithelial and stromal tumor of the kidney in a 14-year-old boy. Urol Int. 2012; 88:247-8. doi: 10.1159/000334335.

8       Turbiner J, Amin MB, Humphrey PA, Srigley JR, De Leval L, Radhakrishnan A, et al. Cystic nephroma and mixed epithelial and stromal tumor of kidney: a detailed clinicopathologic

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