|Year : 2013 | Volume
| Issue : 2 | Page : 125-129
Mesoblastic nephroma in adult: A case with unusual growth pattern
KV Murali Mohan, Vissa Shanthi, BA Rama Krishna
Department of Pathology, Narayana Medical College, Nellore, Dr. NTR University of Health Sciences, Vijayawada, Andhra Pradesh, India
|Date of Web Publication||21-May-2013|
K V Murali Mohan
Staff Q. No. 30, Narayana Medical College, Chintha Reddy Palem, Nellore, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Mesoblastic nephroma (MN) is an uncommon congenital tumor of infancy that rarely occurs in adults. We report a case of cellular MN in a 40-year-old woman. The tumor showed an unusual pattern of growth as an intracystic mass involving the adjacent renal parenchyma. Microscopically, it consisted of spindle cell proliferation with entrapped dilated renal tubules. Cartilaginous islands and numerous atypical mitotic figures were also noted. Spindle-shaped tumor cells show immunoreactivity for vimentin and variable positivity for estrogen and progesterone receptors (ER and PR). Epithelial membrane antigen was positive only in epithelial component. A combination of histological and immunohistochemical findings is useful in the differential diagnosis of cellular MN from other tumors of the kidney with spindle cell component.
Keywords: Immunohistochemistry, mesoblasticnephroma, intracystic mass
|How to cite this article:|
Murali Mohan K V, Shanthi V, Rama Krishna B A. Mesoblastic nephroma in adult: A case with unusual growth pattern. J NTR Univ Health Sci 2013;2:125-9
|How to cite this URL:|
Murali Mohan K V, Shanthi V, Rama Krishna B A. Mesoblastic nephroma in adult: A case with unusual growth pattern. J NTR Univ Health Sci [serial online] 2013 [cited 2019 Nov 14];2:125-9. Available from: http://www.jdrntruhs.org/text.asp?2013/2/2/125/112343
| Introduction|| |
Mesoblastic nephroma (MN) is a rare congenital tumor of infancy first described by Bolende etal. in 1967.  Previously these neoplasms had been identified with different terms; including fibroma, leiomyoma, and leiomyomatous hamartoma.  MN is usually discovered during the first few weeks of life and is often confused with Wilms tumor, but it is almost invariably benign. It usually appears as an unencapsulated tumor composed of spindle cells predominantly, renal tubules that are often cystic, and lack of anaplasia or mitotic activity. The first case of MN in adults was described by Block et al., in 1973.  We report a case of unusual form of MN in an adult patient which presented as intracystic polypoid mass.
| Case report|| |
A 40-year-old woman presented with pain in the left flank. The physical examination and routine laboratory tests were normal. Ultrasound revealed a solid cystic mass in the lower pole of the left kidney with no disruption of capsule. The patient underwent left radical nephrectomy and the specimen was sent for histopathological examination.
Grossly we received left nephrectomy specimen measuring 16 × 10 × 7 cm. Cross section showed grey white nodular cystic tumor measuring10×9×6cm in the lower pole of the kidney distorting lower calyces. The tumor had variegated appearance with area of cystic degeneration, hemorrhages, and necrosis [Figure 1]. The tumor extended to the renal capsule but did not show invasion.
Microscopic examination revealed a tumor that composed of spindle-shaped cells arranged in sheets and fascicles. In some foci the cells were plump [Figure 2]. They had oval to elongated vesicular nuclei with prominent nucleoli [Figure 3]. The epithelial component shows tumor cells arranged in tubular pattern [Figure 4]. Few foci revealed cystic spaces lined by flattened to cuboidal epithelium and hobnail cells [Figure 5]. Islands of cartilage were noted in the midst of the tumor cells. Foci of hemorrhage and necrosis were also noted. The tumor was infiltrating the adjacent renal parenchyma which showed entrapped tubules and glomeruli [Figure 6]. Atypical mitotic figures were also seen.
|Figure 2: Spindle-shaped plump tumor cells having vesicular nuclei (Hematoxylinand Eosin stain (HE),100×)|
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|Figure 3: Tumor cells having vesicular nuclei with prominent nucleoli (HE,400×)|
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|Figure 4: Tumor cells with epithelial component showing attempted tubular formation (HE,100×)|
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|Figure 6: Tumor cells showing infi ltration into the adjacent renal parenchyma (HE,100×)|
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Immunohistochemistry was performed in formalin-fixed, paraffin-embedded tissue sections using the conventional avidin-biotin horseraddish peroxidase method. The results revealed positivity in the majority of spindle cells for vimentin [Figure 7] and focal positivity for estrogen and progesterone receptors (ER and PR) [Figure 8], [Figure 9], The tumor cells lining the tubules revealed epithelial membrane antigen positivity [Figure 10]. S-100 and neuron-specific enolase (NSE) were negative.
|Figure 7: Spindle-shaped tumor cells showing positivity for vimentin (Vimentin,100×)|
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|Figure 10: Tumor cells lining the cystic spaces are EMA positive (EMA,100×)|
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| Discussion|| |
MN is also known as fetal, mesenchymal, or leiomyomatous hamartoma. These tumors usually make up less than 3% of renal neoplasms in children. It is the predominant renal neoplasm in the first 3 months of life and is uncommon after 6 months. 
Adult renal tumors having mixture of epithelial and stromal components have been designated as adult MN, cystic hamartoma of renal pelvis, or solid and cystic biphasic tumor.Some authors believe that the lesions referred to as adult MN has no relation to the childhood MN and that they even lack the genetic alterations typical of cellular congenital MN. 
Grossly the tumors are solid and cystic, tan to yellow, and well circumscribed. These tumors range from 2 to 24 cm. In some cases, cystic component predominates and is associated with solid mural nodules.  Most of these tumors are centered near the hilum of the kidney. Involvement of renal hilum and compression of the pelvicalyceal system is common. However,infiltration into the renal parenchyma is usually not seen. Areas of hemorrhage and necrosis are absent.
Microscopically the tumor is biphasic composed of mesenchymal(stromal) and epithelial components. The mesenchymal component is represented by fascicles and sheets of spindle cells showing variable degrees of smooth muscle, fibroblastic, or myofibroblastic differentiation with interspersed collagen. In some cases the mesenchymal component resembles ovarian stroma. The epithelial component may vary from tubules to complex branching glandular formations to microcysts and macrocysts formation. In some there are leaf-like arrangements resembling those seen in phyllodes tumor.
Some believe that the spindle cells of the tumor have the features of secondary mesenchyme which lacks the capacity to find epithelial structures in contrast to primary mesenchyme or mesoblast.  The proliferating spindle cells acquire the features of fibroblasts, myofibroblasts, or smooth muscle cells.  Most of the tubules which are located at the periphery are considered to result from entrapment of tubules in between the tumor cells. The centrally located tubules with complex appearance may be the component of the tumor. Small islands of hyaline cartilage and foci of extramedullary hematopoiesis may be present. Immunohistochemically,spindle-shaped tumor cells show immunoreactivity for vimentin and ER and PR. Epithelial membrane antigen positivity will be seen in the epithelial component.
In some cases these tumors are very cellular and mitotically active and have tendency to infiltrate the renal pelvis or perirenal tissue and may contain areas of hemorrhage and necrosis. These tumors are referred as cellular or atypical MN.  Ultrastructurally these are similar to infantile fibrosarcoma. 
Our case displayed an unusual growth pattern as a polypoidal intracystic mass with areas of hemorrhages and necrosis. Mitotic activity was high and the tumor showed infiltration into the adjacent renal parenchyma.
A combination of histological and immuno histochemical findings is useful to distinguish MN from other tumors of the kidney with spindle cells. Wilms tumor is rare in adults and can be usually separated from MN by the presence of blastemal component or embryonic tissue. Sarcomatoid renal cell carcinomas show evident cellular atypia and mitosis. Immunohistochemistry and electron microscopy reveal epithelial differentiation in the spindle cell component. Angiomyolipoma is composed of smooth muscle, thick-walled vessels, and adipose tissue. When the smooth muscle predominates, it may also be mistaken for adult MN and many areas of the tumor must be studied. Multicystic nephroma is encapsulated, unilateral, and does not communicate with the pelvis. It is mainly composed of multiloculated cysts with spindle fibroblastic or scattered muscle cells in the septae of the cystic cavities. Nodular solid areas are also absent. Nephrogenic adenofibroma has been described as an entity that occurs in young people (mean age 13.3 year). These neoplasms are usually solitary and nonencapsulated. They show a marked proliferation of epithelium similar to the hyperplastic nephrogenic rests (nephrobastomatosis). Spindle cells in nephrogenic adenofibroma are positive for vimentin but not for actin and desmin, whereas the embryonic epithelium stains positively for keratin but not for epithelial membrane antigen (EMA). Tumor cells will be negative for ER and PR.
Other entities with spindle cells including those of neurogenic, fibrohistiocytic, or vascular origin can be distinguished from MN by nonreactivity for S-100, NSE, alpha-1-antitrypsin, alpha-1-antichymotrypsin, and factor VIII.
The clinical behavior of adult MN is usually benign. But the long-term followup of few patients with atypical MN has shown local recurrence after many years. Inadequate resection of the renal tumor may lead to recurrence, for the lesions showing histologic atypia and zones of necrosis (atypical variant of MN).
| Conclusion|| |
Though the treatment is nephrectomy which is similar to other renal tumors including renal cell carcinoma, careful long-term followup is indicated in those patients with these atypical or cellular MN due to risk of recurrence.
| References|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]