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Thyroid-like follicular renal cell carcinoma (TLF-RCC) is an extremely rare tumor with less than 40 published reports. These tumors are morphologically distinct with striking resemblance to thyroid follicular tumors, but immunohistochemically different due to lack of thyroglobulin and thyroid transcription factor 1 expression. TLF-RCCs arise in younger patients (mean age = 41 years) with female predominance and in all reported cases were solitary tumors without coexisting epithelial or mesenchymal kidney neoplasms. In this article, we report a case of a 42-year-old woman who presented with an incidental 4-cm solid and cystic left renal mass of the upper pole, which was resected. A detailed imaging assessment, pathologic findings, and immunohistochemical studies revealed a partially encapsulated TLF-RCC arising in a background of mixed epithelial and stromal tumor.

Thyroid-like follicular carcinoma of the kidney (TLFCK) is an extremely rare primary renal malignancy that typically has an indolent course and good prognosis. Histologically, this tumor mimics follicular carcinoma of the thyroid; however, typical thyroid markers are negative. There are fewer than 40 cases reported in the literature, and thus, the prognosis and course of disease is not well understood. Sarcomatoid differentiation has never been reported in a case of TLFCK. We present a case of a 48-year-old woman with an aggressive TLFCK with extensive sarcomatoid differentiation and metastatic disease at presentation. We performed targeted next-generation sequencing of both the thyroid-like component and the poorly differentiated sarcomatoid component using our solid tumor panel to evaluate for any disease-associated mutations and to better understand the molecular profile of these tumors.

Mixed epithelial and stromal tumour (MEST) of the kidney, is a recently recognized and rare entity .We herein reported the case of a 56 years old post-menopausal woman who presented with right abdominal pain. Her physical examination was unremarkable. Ultrasonography revealed the presence of a right cystic renal mass in the interpolar region extending into the pelvis. The tumor was considered Bosniak 4 category and a right nephro-ureterectomy was performed. The histological examination of the tumor revealed a mixed tumor with both epithelial and stromal pattern.

The term cystic nephroma has traditionally been used to refer to 2 neoplasms, a lesion in adults that is now thought to be part of the spectrum of mixed epithelial stromal tumor (MEST) and a pediatric lesion that has been associated with mutations in the DICER1 gene. A direct detailed morphologic, immunohistochemical, and genetic comparison of these 2 lesions has not been performed. In this study, we compare the morphologic features, immunoreactivity for estrogen receptor and inhibin, and DICER1 genetic status of 12 adult cystic nephroma/MEST (median age 50.5 y, all females) and 7 pediatric cystic nephroma (median age 1.3 y, male:female=6:1). Both lesions (11 of 12 adult cases, 6 of 7 pediatric cases) frequently demonstrated subepithelial accentuation of stromal cellularity, though the increased cellularity frequently included inflammatory cells in the pediatric cases. All adult and pediatric cases labeled for estrogen receptor; however, whereas most (83%) of adult cases labeled for inhibin at least focally, no pediatric case labeled for inhibin. Most adult cases (58%) demonstrated wavy, ropy collagen in association with cellular stroma, whereas this was not found in pediatric cases. 86% of pediatric cases demonstrated DICER1 mutations, whereas only 1 of 10 adult cases demonstrated a DICER1 mutation. In summary, although cellular stroma and estrogen receptor immunoreactivity are commonly present in both adult and pediatric cystic nephroma, ropy collagen and inhibin immunoreactivity are far more common in adult cystic nephroma/MEST, whereas DICER1 mutations are far more prevalent in pediatric cystic nephroma. These results support the current World Health Organization Classification's separation of adult and pediatric cystic nephromas as distinct entities.

Clear cell papillary renal cell carcinoma is increasingly recognized as a distinct tumor with unique morphology, immunohistochemistry, and cytogenetics. Histopathology often mimics clear cell renal cell carcinoma; however, metastasis has not been reported, emphasizing the clinical value of recognizing these likely nonaggressive tumors. We studied tumors with borderline morphology of clear cell papillary renal cell carcinoma, utilizing immunohistochemistry and fluorescence in situ hybridization or karyotyping. Tumors from 22 patients (ages 33 to 82 y) were analyzed. Clear cell papillary renal cell carcinoma-like morphology varied from 10% to 90% of the tumor (median 25%). Sources of resemblance included: branched glands (95%), nuclear alignment (68%), small papillary tufts (32%), focal branching papillae (27%), and prominent papillary structures (9%). Carbonic anhydrase IX uniformly revealed diffuse positivity. Staining for cytokeratin 7 (CK7) was focal (64%) or negative (18%) in most tumors (82%); however, >50% labeling was present in 4 (18%). Reactivity for both CD10 and α-methyl-acyl-CoA-racemase (AMACR) was usually present (median 80% and 60% of cells). Seven tumors showed reactivity for high-molecular weight keratin (32%). Chromosome 3p loss was confirmed in 15 tumors (68%), including 4/7 with labeling for high-molecular weight keratin or >50% reactivity for CK7. A discordant immunohistochemical pattern typically correlates with loss of material from chromosome 3p in tumors with incomplete morphology of clear cell papillary renal cell carcinoma, supporting classification as clear cell renal cell carcinoma. Diffuse labeling for CK7 can uncommonly be observed in clear cell renal cell carcinomas confirmed to have chromosome 3p loss, although these do not exhibit the expected staining pattern of clear cell papillary renal cell carcinoma, including positivity for CD10 and AMACR.

Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET) is a childhood malignancy, typically occurring in the bone and rarely in any other part of the body. We herein present a case of ES/PNET of the renal pelvis. A 37-year-old male patient presented with a chief complaint of pain in the left flank and gross hematuria. The tumor had caused moderate hydronephrosis, and ureteroscopic biopsy findings were highly suspicious of sarcoma. Subsequently, radical nephroureterectomy was performed. On the basis of the pathological and cytogenetic findings, a final diagnosis of primary ES/PNET of left renal pelvis was made. Adjuvant chemotherapy with adriamycin and ifosfamide was initiated as ES/PNET often exhibits aggressive biological behavior. The patient was disease-free at his last regular follow-up visit 18 months after the surgery. To our knowledge, this is the first reported case of primary ES/PNET of the renal pelvis.

A 32-year-old woman presented with left abdominal pain. Intratumoral hemorrhage within a renal angiomyolipoma (AML) was suspected and embolization was performed. However, the patient declined surgery and was thus kept under observation. During the next 5 years, the tumor increased in size, and upper left abdominal pain appeared. Therefore, left radical nephrectomy was performed. The histopathological diagnosis was mixed epithelial and stromal tumor (MEST) of the kidney. A retrospective examination of imaging findings indicated that the fat which had been regarded as evidence of AML was actually either perinephric fat displaced by either the tumor or the renal sinus. In fact, the tumor consisted mainly of a cystic component containing a solid component. The possibility of MEST must be kept in mind when distinguishing renal tumors consisting mainly of cystic components in young to middle-aged women.

Co-existence of angiomyolipoma (AML) and renal cell carcinoma (RCC) in the same tumor mass is very rare and only eight cases have been reported. We present a case of a young female with tuberous sclerosis complex (TSC) with bilateral huge renal AMLs. Both tumors were removed, one of which revealed co-incidental RCC. She was subsequently successfully transplanted a kidney from her brother and is maintaining normal graft function eight months post-transplant. No recurrence or metastases of RCC has been detected till the last follow-up.

Mixed epithelial and stromal tumor (MEST) of the kidney is a rare, typically benign lesion that occurs predominantly in perimenopausal women. At computed tomography (CT), it typically manifests as a multiloculated cystic renal mass with a variable proportion of solid and cystic components and containing internal septa that demonstrate heterogeneous and delayed contrast material enhancement. MEST may mimic a variety of benign and malignant renal lesions, such as adult cystic nephroma, complex renal cyst, and cystic renal cell carcinoma. The preoperative diagnosis of MEST can be problematic, and most cases are treated surgically. However, CT with two-dimensional multiplanar reformation and three-dimensional volume rendering helps define the diagnostic features of MEST and can assist in surgical planning., (© RSNA, 2010.)

Mixed epithelial and stromal tumors (MESTs) of the kidney are rare renal neoplasms characterized by mixed cystic and solid components. These tumors are typically present in middle-aged women as a flank mass, or as a cause of flank pain or hematuria. We outline the case of an older male who presented with an enlarging abdominal mass causing symptoms that suggested a partial small bowel obstruction. Management of the patient and a brief review are discussed.

Although first intimated in the 1970s, mixed epithelial stromal tumor has been recognized as a diagnostic entity for less than 10 years, with an identity that has been challenged by overlap between other cystic renal neoplasms, most notably with cystic nephroma. We report the first case of a bilateral mixed epithelial stromal tumor occurring in a 41-year-old dialysis-dependent woman, notably also the first case reported in a patient with end-stage renal disease. The neoplasms occurred 5 years apart and were diagnosed as mixed epithelial stromal tumor in both instances. We describe the presentation and pertinent radiologic, histologic, and immunophenotypic findings of these neoplasms with a review of the current debate regarding mixed epithelial stromal tumor and cystic nephroma taxonomy.

A 51-year-old, perimenopausal, female patient with 1-month history of right flank pain who was diagnosed with a renal mass and underwent nephron-sparing partial nephrectomy is presented. The renal mass was found to be a benign, biphasic tumor composed of an epithelial component, consisting of ducts of variable size scattered within a mesenchymal component, composed of spindle cells arranged in sheets and fascicles. No atypia, mitosis, or necrosis was found. The spindle component shows desmin, smooth muscle actin, and estrogen and progesterone receptor positivity immunohistochemically. The diagnosis of benign mixed epithelial and stromal tumor of the kidney is rendered. No recurrent disease has been detected during 2 years of follow up.

The recently described mixed epithelial and stromal tumor (MEST) of the kidney and adult cystic nephroma (CN) (multilocular cyst) are rare benign cystic renal neoplasms that are composed of epithelial and stromal elements. Consensus criteria for distinguishing these entities have not been well established. Our objective in this study was to evaluate cases of CN and MEST to define the morphological, immunophenotypic, and clinical features of these two entities. Eleven cases from the files of a single institution diagnosed from 1996 to the present as either CN or MEST were reviewed. Architecturally, all lesions were composed of multiple noncommunicating cysts lined by a single layer of epithelial cells. All cases had areas with increased stromal cellularity and 8 cases had ovarian-like stroma present at least focally within the tumor. No stromal or epithelial cell atypia, blastemal elements, or increased mitotic activity was appreciated. The immunoprofile was also similar in the 7 cases stained and included epithelial reactivity with keratin and CAM 5.2 and stromal reactivity with estrogen receptor, progesterone receptor, smooth muscle actin, WT-1, vimentin, and focal desmin. All cases have acted in a benign fashion with no history of recurrence or metastasis. We propose that CN and MEST of the kidney represent a spectrum of the same entity. If the diagnosis of CN is limited to cases that are comprised entirely of thin fibrous-walled cysts, all 11 of our cases would be classified as MEST.

Three cases of mixed epithelial and stromal tumor of the kidney with their imaging findings are described; these cases have not been reported previously in the radiology literature. This benign tumor contains epithelial and spindle cell stromal components and arises exclusively in adult women. It is characterized morphologically by a solid and cystic nature with delayed enhancement.

Context: Mixed epithelial-stromal tumor of the kidney is a recently recognized benign renal tumor that usually occurs in adult women and typically forms a sizable lesion with solid and cystic areas. The recognized morphologic spectrum of this recently described entity is evolving., Objective: To review the clinicopathologic features of 3 small mixed epithelial-stromal tumors of the kidney that were incidental findings in kidneys removed for other reasons., Design: The clinical presentation and morphologic findings of the 3 cases were reviewed. A panel of immunohistochemical stains was performed., Setting: Academic medical center., Results: All 3 lesions contained predominantly fascicles of smooth muscle mimicking leiomyoma, but they also had cellular subpopulations of smaller, müllerian-appearing stromal cells. Tubules present within the lesion were most abundant at the periphery, suggesting that they might be entrapped. Although only the spindled smooth muscle cells were immunoreactive for muscle markers desmin and actin, both the spindled smooth muscle cells and the cellular müllerian-appearing stromal cells demonstrated diffuse nuclear labeling for estrogen and progesterone receptors., Conclusions: Mixed epithelial-stromal tumor of the kidney may present as an incidental stromal-predominant lesion within the kidney. Such lesions are easily confused with leiomyomas or stromal-predominant angiomyolipomas.

We report a case of asymptomatic mesoblastic nephroma in a 54-year-old woman. The tumor showed immunohistochemical reactions similar to developing nephrons. Electron microscopy showed immature tubules with numerous intracytoplasmic intermediate filaments. Recent studies support the concept of pathogenesis of the mesoblastic nephroma originating from collecting ducts. However, this case exhibited a complex pattern of antigenic expression not restricted to the collecting ducts, but including the glycoprotein CD24 and the neural cell adhesion molecule (NCAM). The following differential diagnoses will be discussed: benign mixed epithelial and stromal tumor, metanephric adenoma, and nephrogenic adenofibroma.