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Fine needle aspiration biopsy (FNAB) of the kidneys is a safe procedure with an excellent diagnostic yield based on established criteria for primary lesions with a sensitivity of 80% to 92% and specificity of 83% to 100% in diagnosing malignancy. The use of rapid on-site evaluation of the FNAB can reduce the need for core biopsy. But there are benefits to using a combined fine needle biopsy (FNAB) and core biopsy approach, to increase specificity of the malignant diagnosis, to subtype carcinomas, and to provide material for ancillary studies including molecular studies, although increasingly these can be performed on cell block material from the FNAB or direct smears. The cell block material can be used for histologic assessment, immunohistochemistry (IHC), fluorescent in situ hybridization (FISH), cytogenetic techniques, and molecular analysis for specific gene expression profiling. Ideally, the cytopathologist should be experienced in reporting FNAB of the kidney or working on a team of cytopathologists experienced in renal biopsies. However, the complementary roles of FNAB and core biopsy will depend on institutional approaches and local expertise.
Ideally a cytopathologist or at least a well-trained cytotechnologist should be in attendance to provide rapid on-site evaluation (ROSE), give an immediate assessment of adequacy and need for further FNAB passes and core biopsy, and ensure correct handling of the specimen and selection of appropriate ancillary tests. The percutaneous FNAB can be carried out through a coaxial cannula to minimize the risk of needle track seeding, which is negligible; reduce patient discomfort due to multiple needle sticks; and aid imaging of the needle site. In cases where there is dual pathology with possible lymph node and gastrointestinal lesions, endoscopic ultrasound (EUS) FNAB of the renal lesion should be considered.
Traditionally, FNAB of the kidney was used to make a preoperative diagnosis to avoid unnecessary nephrectomy. With the increase in lesions detected incidentally during abdominal screening by computed tomography (CT) and magnetic resonance imaging (MRI) for the workup of metastatic disease and hypertension, there has been an increase in the interest in and indications for renal FNAB, especially in small lesions (<3 or 4 cm) that include :
Primary versus metastatic carcinoma
Abscesses and other infections
Lymphomatous involvement of the kidney
Inoperable large tumors
Tumors in the elderly and infirm
Tumors in patients with known malignancy elsewhere
Low-grade tumors such as angiomyolipoma and low-grade renal carcinomas
Small renal tumors
Preablation therapy
A significant percentage, up to 33.6%, of solid renal masses less than 4 cm are benign, and FNAB and complementary core biopsy in these cases reduce the number of patients committed to open or laparoscopic, partial or complete nephrectomy. The tumor type diagnosed on FNAB, cell block, and core biopsy will determine the selection of the treatment: laparoscopic nephrectomy, partial nephrectomy, percutaneous ablative treatment or chemotherapy, immunomodulating therapy, and newer developing modalities such as tumor vaccines, vascular endothelial growth factor modulators, and stem cell transplantation.
The classification of renal tumors based on molecular parameters in addition to cytomorphology and IHC facilitates the use of new therapies. FNAB with ROSE can triage cases and provide additional material with minimal cost to the patient and medical system, minimal morbidity, and rapid diagnosis. FNAB can sample more of a tumor than core biopsy, which is particularly important when assessing possible Wilm tumors in which blastema, epithelial, and stromal components may be focal and when diagnosing sarcomatous lesions seeking confirmation of origin in a renal carcinoma, but there are benefits to using the two biopsy techniques.
FNAB advantages are enhanced in a multidisciplinary setting that includes a cytopathologist, clinician, and radiologist, and renal FNAB is best performed in a referral hospital setting because of the relative rarity of renal tumors and the need to select the most appropriate cost-effective ancillary tests. All of the advantages of renal FNAB are increased in the pediatric setting, where rapid diagnosis is required, cytogenetics and molecular studies greatly assist the diagnosis and can be based on FNAB material with or without core biopsy, and preoperative and pretreatment diagnosis are mandatory.
Complications of FNAB are rare including transient hematuria and a theoretical risk of needle track implantation, although if this occurs it is usually more likely due to core needle biopsy.
The definition of an adequate renal FNAB is controversial, and there is no consensus. Cystic lesions and lesions with low cellularity may be incorrectly called benign, while inflammatory lesions that consist of inflammatory cells and fibrosis may be called inadequate but may represent the lesion and be better termed nondiagnostic or negative. A renal FNAB should only be called “adequate” if a specific benign or malignant diagnosis can be made or a differential diagnosis (DD) is established. Unsatisfactory FNAB are related to small lesions, less than 4 cm, that are technically more difficult to sample and large lesions, greater than 6 cm, where the tumors are frequently extensively necrotic. The crucial requirement is that the procedure requires CT or ultrasonic guidance, and correlation with imaging is mandatory.
Categories to distinguish renal FNAB have been proposed :
Unsatisfactory (inadequate cellularity)
Nondiagnostic (adequate cellularity consisting of normal renal elements that are not representative of the lesion, where there is high suspicion on imaging and clinical findings of malignancy)
Negative (adequate cellularity consisting of normal renal elements that are representative of the lesion, where there is low suspicion on imaging and clinical findings of malignancy)
Atypical
Suspicious (in a spectrum of an increasing number and atypia of cells “inconsistent with normal renal elements”)
Positive (definitive neoplastic cells)
This categorization requires on-site knowledge of the imaging findings and a multidisciplinary approach, ideally with ROSE.
The accuracy of grading renal cell carcinomas (RCC) by FNAB is not as accurate as that achieved on excision surgical specimens, due to small sample size, heterogeneity of tumors, and the subjectivity of Fuhrman grading of RCC, but when tumors are graded simply as low (Fuhrman grade I-II) or high (Fuhrman grade III-IV), then agreement between 87% and 100% can be achieved.
The classification of renal tumors in the 2004 World Health Organization text has been changing with new entities, and an International Society of Urological Pathology Vancouver Modification of the histologic classification has been published ( Table 9-1 ). New entities, such as tubulocystic, acquired cystic disease associated, clear cell (tubulo) papillary, MiT family translocation, and hereditary leiomyomatosis have been included and older entities reviewed. FNAB cytology reports and diagnostic criteria for many of these lesions have not been established, but a brief discussion is included in this text so that awareness of these lesions and their potential diagnosis by FNAB can be facilitated. Not all lesions, especially rare primary sarcomas similar to those found elsewhere in the body, are discussed here. The ordering of renal tumors in Table 9-1 has no relation to the FNAB cytology patterns presented in this text.
Renal cell tumors |
|
Occurring mainly in children |
|
Occurring mainly in adults |
|
∗ Additions and changes in terminology or position in classification.
The increased role of IHC using renal FNAB material and core biopsies has been driven by the need for specific diagnoses of metastatic RCC (up to 30% of renal primaries present with metastases) and for the diagnosis of subtypes of primary renal neoplasms to determine management: nephrectomy versus nephron-sparing surgery, cryoablation versus radiofrequency, molecular targeted therapies, appropriate chemotherapy, and in some cases, observation of small low-grade tumors.
Table 9-2 presents the IHC of the subtypes of renal neoplasms. Combining cytomorphology and cell block histologic features with a basic IHC panel of CK7, CD10, CAIX, AMACR (P504s), and CD117 can differentiate most RCC. When assessing a renal cell neoplasm with clear and admixed eosinophilic cells, clear cell carcinoma will be positive for AE1/AE3, vimentin, PAX2, PAX8, CD10, carbonic anhydrase IX (CAIX), and RCC marker. It will be negative for DOG1, CD117, and CK7, while the chromophobe carcinoma and oncocytoma will be positive for DOG1, AE1/AE3 pankeratin, CD117, E-cadherin, and kidney-specific cadherin and negative for vimentin and CAIX.
Pankeratin | CK7 | CK5/6 | CK20 | CD10 | EMA | PAX2/ PAX8 |
RCCM | CAIX | DOG1 | CD117 | E-cadherin | Vimentin | CD117 | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Clear cell carcinoma | + | − | − | − | + | + | + | + | + | − | − | + | − | |
Papillary carcinoma | + | + | − | − | + | + | + | + | − | + | − | |||
Mucinous tubular and spindle carcinoma | + | + | + | + | − | |||||||||
Urothelial carcinoma | + | + | + | + | − | − | − | − | ||||||
Chromophobe carcinoma | + | + | − | − | ± | − | − | + | + | + | − | + | ||
Oncocytoma | − | ± | − | − | − | − | − | + | + | + | − | + | ||
Collecting duct carcinoma | + | + | + | |||||||||||
Xp11.2 Translocation | − (focal +) | + | + |
Differentiation of the chromophobe renal carcinoma and oncocytoma on IHC is controversial, but HNF1Beta and S100A1 stain a greater proportion of tumor cells and show stronger staining in oncocytomas than in chromophobe carcinoma, which is rarely if ever positive in both these markers. Further, cyclin D1 is positive in oncocytomas but negative in chromophobe carcinoma and clear cell carcinoma, and CK7 is positive in chromophobe carcinomas but negative in oncocytomas and clear cell carcinoma apart from scattered single positive cells. A new stain for amylase alpha-1A (AMY1A) stains oncocytomas but very few chromophobe carcinomas, as well as distal tubules and collecting ducts.
Carcinomas with a papillary pattern including papillary, mucinous tubular, and Xp11.2 carcinomas will be positive for CK7, AMACR, PAX2, PAX8, and CD10, 34,35 while CD57 will support metanephric adenoma and TFE3 will diagnose the translocation carcinoma when positive in 100% nuclei.
When faced with a “small blue cell tumor,” leukocyte common antigen/CD45 (lymphoma), WT1 (Wilm tumor), CD99 (primary Ewing sarcoma), synaptophysin and chromogranin (neuroblastoma, neuroendocrine carcinoma), and AE1/AE3 pankeratin (synovial sarcoma) form a useful panel. Sarcomatous RCC usually show weak positivity for CD10, PAX2, or PAX8 and renal cell marker.
For possible metastatic renal carcinoma lesions, a panel of pancytokeratin, vimentin, PAX2 or PAX8 with RCC marker or CD10, is recommended along with other specific markers related to clinical history and site (e.g., TTF-1 for possible lung primaries, prostate-specific antigen [PSA] or prostein for prostate carcinomas [these are also positive for AMACR, which is positive in metastatic papillary RCC]). PAX2 and PAX8 are positive in almost all renal carcinomas, but both are positive in ovarian and endometrial carcinomas; PAX8 is also positive in thyroid carcinomas. Vimentin coexisting with CK positivity is only seen in RCC (except chromophobe carcinoma), thyroid, endometrial, and adrenal cortical carcinoma. CK7 is negative in clear cell carcinoma but positive in all papillary, collecting duct, and urothelial carcinomas, and the latter two are positive in CK5/6. CD10 is positive in almost all clear cell and papillary carcinomas and negative in other renal carcinomas but is positive in other malignancies.
Other markers include E-cadherin, kidney-specific cadherin, and CD117 (positive in chromophobe renal carcinoma and oncocytomas, negative in clear cell and papillary carcinomas), alpha-methylacyl-coenzyme A racemase/AMACR (positive in papillary renal and prostate carcinoma), P63 (positive in urothelial but not renal carcinomas), CD57 (metanephric adenoma), and HMB45 and melan A (angiomyolipoma).
CAIX is a marker related to the von Hippel Lindau pathway and, when strongly expressed in renal carcinomas, suggests a better prognosis and better response to interleukin-2 immunotherapy.
Comparative genomic hybridization on FNAB and biopsy material to demonstrate chromosomal abnormalities may offer improvements in cytomorphologic and IHC diagnosis of renal carcinoma subtypes : Clear cell carcinomas have losses at chromosome 3p, papillary carcinoma whole chromosome gains of 7,12,16 and 17, chromophobe carcinomas several whole chromosome losses at 1,2,6,10,13,17,21, X and/or Y, and oncocytomas may have loss of 1p, 14 or Y, translocations involving 11:13, gain of 11, or a normal karyotype. FISH using multiple probes can distinguish clear cell and papillary carcinoma.
Recognition at low power of the pattern of a renal smear includes assessment of epithelial and nonepithelial tissue fragments and dispersed cells, fibrovascular strands and stromal components, inflammatory cells, and the presence of necrosis and hemorrhage in the background and is the first step to making the correct diagnosis. There are eight patterns in renal FNAB, and each pattern and its minor variations raises a DD of benign and malignant tumors ( Plates 9-1 to 9-8 ). In some cases the carcinoma may have heterogeneous features that could place it in a number of patterns, for instance, Xp11.2 carcinomas, but the pattern recognition provides a starting point and the individual components can be confirmed at high power. Other tumors do not place easily in any of the eight patterns, but one or more elements of their features do and provide a first impression and DD.
Normal kidney, with small tissue fragments of proximal convoluted, distal convoluted, collecting tubules, loops of Henle, and glomeruli, in a clean background
Metanephric adenomas
Renal cysts
Hematomas
Acute pyelonephritis
Chronic pyelonephritis
Granulomatous pyelonephritis
Xanthogranulomatous pyelonephritis
Malakoplakia
Lymphoma
Clear cell renal carcinoma
Collecting duct carcinoma
Juxtaglomerular body tumor
Chromophobe renal carcinoma
Oncocytoma
Type 1 papillary renal carcinoma
Type 2 papillary renal carcinoma
Xp11.2 translocation/ TFE3 fusion carcinoma
Mucinous tubular and spindle cell carcinoma
High-grade renal carcinomas
Sarcomatous renal carcinoma
Metastatic carcinomas
Urothelial carcinoma of renal pelvis
Rhabdoid tumor
Nephroblastoma (Wilm tumor)
Mesoblastic nephroma
Angiomyolipoma
Smear Pattern: Mixed Small Tissue Fragments in Clean Background With or Without Glomeruli
Pattern: mixed renal tissue fragments in clean background with or without glomeruli.
Proximal convoluted tubules are usually the most prominent component consisting of large cells singly or in flat, syncytial sheets with copious pinkish-gray (Giemsa) or eosinophilic (Papanicolaou [Pap]) finely granular cytoplasm and central small round nuclei and small nucleoli; may have pink stromal strands.
Distal convoluted tubules consist of smaller cells in syncytial sheets.
Loops of Henle and collecting tubules have smaller cells in compact flat sheets, with scanty dense cytoplasm with or without coarse lipofuscin pigment and small, dark, round nuclei.
Glomeruli are large, irregular, lobated tissue fragments of looped capillaries and spindle endothelial cells.
These normal components of kidney may be found alone, raising the possibility that the lesion is normal kidney or that the FNAB has missed the target, or may be mixed with cells from a neoplastic or non-neoplastic lesion.
Smear Pattern: Mixed Small Tissue Fragments in Clean Background With or Without Glomeruli
These rare, benign tumors are derived from metanephric blastema; constitute 0.2% of adult renal neoplasms; and occur most commonly in adult women but also in children where the clinical and imaging DD is Wilm tumor. Occasionally, cases have been reported to metastasize. These tumors usually present incidentally on imaging but may produce abdominal or flank pain, hematuria, polycythemia, or hypertension. Imaging shows a well-circumscribed, hyperechoic mass on ultrasound and a solid homogeneous lesion on CT scan.
The histology shows a nonencapsulated, clearly demarcated tumor, up to 15 cm in size, with small acini and primitive tubules and glomeruloid structures, and in some cases a papillary component and psammoma bodies. The nuclei are round to oval, bland, and closely spaced. Minimal eosinophilic or clear cytoplasm exists in the acini, and there is scant fibrovascular hyalinized stroma.
Management is partial or, rarely, complete nephrectomy, percutaneous radiofrequency ablation, or active surveillance.
Cellularity: moderate.
Pattern: mixed small tissue fragments in clean background with or without glomeruli.
Minute, crowded, cohesive sheets often with microacinar pattern or resembling tubules, and some single cells in clean background.
Tubulopapillary tissue fragments, some with pink stromal cores, and tubular tissue fragments with evenly spaced nuclei surrounded by magenta (Giemsa) or blue (Pap) basement membrane type material. Occasionally, dense glomeruloid tissue fragments.
Occasionally, psammoma bodies.
Small round to oval cells with scant cytoplasm, high N:C ratio, round, overlapping bland nuclei, fine chromatin, inconspicuous nucleoli, and occasionally inclusions and grooves.
There is a lack of necrosis, siderophages, papillary tissue fragments with fibrovascular cores, histiocytes, nuclear atypia, psammoma bodies and mitoses.
The DD includes low-grade papillary RCC, which shows a higher degree of nuclear atypia, siderophages, and a bloody, often necrotic background and is cytokeratin (CK) and epithelial membrane antigen (EMA) positive and negative in WT1 staining, and Wilm tumor with its often triphasic or biphasic pattern, frequent necrosis, larger blastema cells with a higher degree of nuclear pleomorphism, and negative CK7 in the blastema. But some regions of Wilm tumors can be similar to the microacinar pattern of metanephric adenoma. Wilm tumors have specific deletions of the short arm of chromosome 11 and long arm of chromosome 16.
Renal adenomas can be virtually indistinguishable on cytology, with their sheets and acinar tissue fragments of uniform cells with scant cytoplasm and round, small nuclei with even chromatin, but are usually less than 1 cm in size, stain with keratins and EMA, and have trisomies of chromosomes 7 and 17 on FISH.
The IHC shows the tissue fragments to be AE1/AE3 pankeratin, PAX2, and CD57 positive and RCC marker, EMA, CK7, and AMACR negative, while the WT-1 is variably reported but most often negative.
Smear Pattern: Cystic Proteinaceous Background With Variable Number of Macrophages
Renal cysts are frequently diagnosed incidentally by CT and ultrasound or in the workup of patients with hypertension or hematuria. Ultrasound-directed FNAB can be employed when the features are not diagnostic of a benign cyst or show a complex cystic mass. However, a significant number of cases without an epithelial component in the cyst fluid will turn out on surgical excision to be malignant lesions.
Cellularity: scant epithelial components.
Pattern: cystic proteinaceous background with variable number of macrophages.
Variable numbers of macrophages, degenerate cells, and usually scant epithelial cells in a granular proteinaceous background.
Epithelial cells, when present, are small and of uncertain type.
Some nuclear atypia can be present in the degenerating cells.
When present in large numbers, siderophages and necrosis suggest possible RCC with cystic degeneration, as does finding clear cells or distinct papillary tissue fragments. Multilocular cystic RCC is a subtype of clear cell carcinoma and has a better prognosis. Distinction from clear cell carcinoma with cystic degeneration requires histopathology.
The DD also includes: multilocular cystic nephromas, which typically have minute epithelial tissue fragments resembling histiocytes with low N:C ratio and a hobnail placement of nuclei, which at times can show some atypia, along with minute tissue fragments of spindle cells in a cystic background; and a spectrum of lesions including mixed epithelial and stromal tumors, which show a similar bimodal pattern of hypocellular to myxoid to ovarian stroma and hobnail epithelial tissue fragments derived from the cyst lining with minimal nuclear atypia. The epithelium in these tumors is CK, vimentin, and estrogen and progesterone receptor positive, while the stroma is vimentin, smooth muscle actin, and desmin positive and HMB45 and CD117 negative. These rare tumors occur almost exclusively in women (F:M, 10:1) over a broad age range but most commonly around menopause with an average age of 56. Imaging shows a circumscribed solid or multiloculated cystic lesion in the renal cortex.
Smear Pattern: Cystic Proteinaceous Background With Variable Number of Macrophages
There may be a history of trauma, or the lesion may be discovered on routine imaging. FNAB produces yellow- to brown-stained thin fluid.
The DD is that of renal cysts with hemorrhage and renal carcinomas with hemorrhage, and correlation with history and imaging is required.
Smear Pattern: Predominantly Dispersed Inflammatory Cells
There may be a long history of recurrent urinary tract infections, with or without urinary tract surgery for congenital abnormalities and dysfunction. The chronic infection is most commonly associated with Escherichia coli and other gram-negative bacteria but can be associated with Mycobacterium tuberculosis and schistosomiasis. The imaging is variable but can be that of a mass lesion associated with distortion of the collecting system including the renal pelvis.
Cellularity: variable inflammatory cells with usually scant epithelial components.
Pattern: predominantly dispersed inflammatory cells.
Plentiful macrophages and histiocytes in xanthogranulomatous pyelonephritis with lymphocytes, debris, and scattered renal tubules.
Histiocytes have low N:C ratio, eccentric granular cytoplasm, and irregular, often bean-shaped nuclei.
In malakoplakia the macrophages have discrete large basophilic structures (calcium and iron components) in the cytoplasm in a chronic inflammatory background of lymphocytes, plasma cells, and other histiocytes (see Plate 9-3B ; Fig. 9-12 ).
Malignant lymphomas do occur as rare primary lesions in the kidney, presenting in an older patient with flank pain or usually as a single renal mass found incidentally ( Fig. 9-13 ). However, in the majority of cases the lymphoma represents extension from other sites and renal involvement is detected during routine follow-up for lymphoma or other malignancies often as bilateral renal and adrenal masses. Lymphomas are diagnosed as primary lymphomas of the kidney if there is a dominant renal mass with or without renal failure and no history of lymphoma. Primary renal lymphomas possibly arise in a background of chronic inflammation or from the capsule or as a post-transplant lymphoproliferative disorder in a transplanted kidney. The CT features of a hypovascular mass or several masses are different to renal carcinoma, which is hypervascular in contrast-enhanced studies, but raise a DD of pyelonephritis or abscess. FNAB is required to exclude a renal carcinoma leading to nephrectomy versus lymphoma, which requires chemotherapy versus a metastasis from another site. Renal carcinomas are also increased in patients with a known history of lymphoma. FNAB with ROSE can identify the lymphoid nature of the lesion, and flow cytometry can be selected to confirm the diagnosis in almost all cases.
The lymphomas are almost always B-cell lymphomas and usually diffuse large B-cell lymphoma, Burkitt or follicular lymphoma, or acute lymphoblastic lymphoma, but CLL/small lymphocytic lymphoma and marginal zone lymphoma do occur. The commonest cytology is a monotonous large atypical lymphoid population with lymphoid cytoplasmic fragments in a background with necrosis.
Although large cell lymphomas can be diagnosed on cytomorphology, flow cytometry is a useful complementary test and is generally required. FISH or gene rearrangement studies can be diagnostic in, for instance, Burkitt lymphoma or ALL, based on rinsings of the FNAB needle into saline or RPMI.
Smear Pattern: Loosely Cohesive Tissue Fragments With Thin Fibrovascular Strands and Dispersed Cells With Eosinophilic or Clear Cytoplasm With or Without a Hemorrhagic and/or Necrotic Background
Clear cell carcinoma comprises 70% of RCC and can be associated with chromosome 3p deletions (FISH probes or karyotyping). It also occurs in von Hippel-Lindau disease (average age 37 VS sporadic 61). There may be mutation of the VHL gene and hypermethylation of VHL promoter.
The presentation can be a renal mass on imaging workup of a patient with abdominal pain, abdominal mass, or hematuria, or as an incidental renal mass found on imaging for other reasons such as workup of a lung primary carcinoma, or as a metastasis to lymph nodes or other organs including thyroid, bone, or lung. Classically, RCC metastases can occur late, and their “clear cell” cytologic features enter the DD for “clear cell carcinomas” in many other organ sites including pancreas and thyroid.
Cellularity: varies with grade, usually moderate.
Pattern: loosely cohesive tissue fragments of polygonal cells with thin fibrovascular strands and dispersed cells with eosinophilic or clear cytoplasm with or without a hemorrhagic and/or necrotic background.
Sheets and variable single cells and stripped nuclei, which increase with grade.
Background of old blood varies, along with siderophages and often necrotic debris.
Sheets or acinar tissue fragments, with polygonal cells attached to strands of pink (Giemsa) stroma and thin capillaries.
Cytoplasm is usually copious, pale, granular, or vacuolated (rarely totally “clear”), and the N:C ratio is low to moderate, with distinct cell margins.
Hyaline eosinophilic globules in cytoplasm may be present.
Nuclei vary with the grade from central round and relatively small in low-grade tumors to large with hyperchromasia and large single nucleoli in high-grade tumors.
Common intranuclear pseudoinclusions.
Nucleoli are single small varying to large macronucleoli in high-grade tumors.
Low-grade clear cell carcinomas have a DD of chromophobe RCC with their more copious eosinophilic granular cytoplasm and central, round, bland nuclei lacking prominent nucleoli (see Figs. 9-52 to 9-59 ) and, to a lesser extent, oncocytomas (see Fig. 9-60 ). Xp11.2 carcinoma can have clear cells, but usually has papillary architecture, and is Xp11.2 positive. It should be noted that some clear cell renal carcinomas can be S-100 positive and, rarely, HMB-45 and melan A positive.
Multilocular cystic renal cell neoplasm of low malignant potential (multilocular cystic RCC), formed exclusively of variably sized cysts lined by attenuated and often denuded flat to cuboidal epithelium with grade 1 clear tumor cells in the intervening septa, is seen as at one end of a spectrum with cystic clear cell carcinoma at the other end and has a good prognosis.
High-grade clear cell (see Figs. 9-23 to 9-31 ), papillary type 2 (see Figs. 9-40 to 9-47 ), collecting duct (see Figs. 9-35 to 9-38 ), and urothelial cell carcinomas (see Figs. 9-75 to 9-79 ) and some metastases (see Figs. 9-61 to 7-72 ) can be hard to distinguish on cytology. IHC and cytogenetics are required.
Anaplastic tumors in the kidney include high-grade RCC, sarcomatoid carcinomas, and rhabdoid tumors. Sarcomatoid RCC (see Figs. 9-29 to 9-31 ) are regarded as the most “dedifferentiated” tumors and when detected at FNAB at ROSE should lead to a request for further passes because it is important to identify any residual, more specific renal carcinoma, most commonly a chromophobe carcinoma. FNAB offers advantages over core biopsy in this situation because it allows wider sampling of the often inoperable or metastatic carcinoma. The DD includes rare high-grade leiomyosarcomas and high-grade lymphomas. Cell block preparation with IHC is essential.
Rhabdoid tumors occur most commonly in the pediatric setting, where they form 2% of renal tumors and are highly aggressive with a poor prognosis (see Figs. 9-82 to 9-85 ). They are rare in adults, in whom rhabdoid differentiation in a RCC is more common and again signifies a poor prognosis. Electron microscopy (EM) is useful in the diagnosis of rhabdoid tumors in children.
Clear cell (tubulo) papillary RCC has recently been established as a possible separate entity with similar histology and, potentially, FNAB cytology to classic clear cell carcinoma. It is seen in end-stage renal disease, as well as sporadically, and has indolent behavior. The well-circumscribed small tumors have a variable branching tubular, acinar, cystic, or papillary pattern, separated by fibrous stroma that can have prominent myoid differentiation. The epithelial cells have clear cytoplasm, low nuclear grade, and nuclei arranged off the basement membrane in linear fashion, with no necrosis or foamy macrophages. The tumors have characteristic CK7 diffuse positivity and are CA-IX positive, as well as CD10, RCC, and AMACR negative, in distinction to clear cell carcinomas.
Juxtaglomerular body tumors are rarely reported in FNAB cytology but may have a bloody background with old blood and siderophages and enter the DD of clear cell carcinomas. These usually small tumors are found in young patients being investigated for long-standing hypertension, with high plasma renin levels, specifically on unilateral renal vein sampling, and secondary hyperaldosteronism. FNAB smears show low cellularity with small sheets of small cells with indistinct cell borders and granular cytoplasm and central minimally hyperchromatic or pleomorphic round nuclei. In some cases poorly defined connective tissue stalks containing tumor cells are seen along with calcifications, but no definite papillary structures are seen. The distinction from low-grade clear cell carcinoma is assisted by IHC, which shows the juxtaglomerular body tumors to be vimentin, renin, CD117, CD34, and neuroendocrine marker positive, and AE1/AE3 pankeratin, CK7, EMA, and S100 negative. EM shows diagnostic spherical and angulated rhomboid renin granules.
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