- •Preface
- •Acknowledgments
- •Contents
- •1.1 Introduction
- •1.2 Normal Embryology
- •1.3 Abnormalities of the Kidney
- •1.3.1 Renal Agenesis
- •1.3.2 Renal Hypoplasia
- •1.3.3 Supernumerary Kidneys
- •1.3.5 Polycystic Kidney Disease
- •1.3.6 Simple (Solitary) Renal Cyst
- •1.3.7 Renal Fusion and Renal Ectopia
- •1.3.8 Horseshoe Kidney
- •1.3.9 Crossed Fused Renal Ectopia
- •1.4 Abnormalities of the Ureter
- •1.5 Abnormalities of the Bladder
- •1.6 Abnormalities of the Penis and Urethra in Males
- •1.7 Abnormalities of Female External Genitalia
- •Further Reading
- •2.1 Introduction
- •2.2 Pathophysiology
- •2.3 Etiology of Hydronephrosis
- •2.5 Clinical Features
- •2.6 Investigations and Diagnosis
- •2.7 Treatment
- •2.8 Antenatal Hydronephrosis
- •Further Reading
- •3.1 Introduction
- •3.2 Embryology
- •3.3 Pathophysiology
- •3.4 Etiology of PUJ Obstruction
- •3.5 Clinical Features
- •3.6 Diagnosis and Investigations
- •3.7 Management of Newborns with PUJ Obstruction
- •3.8 Treatment
- •3.9 Post-operative Complications and Follow-Up
- •Further Reading
- •4: Renal Tumors in Children
- •4.1 Introduction
- •4.2 Wilms’ Tumor
- •4.2.1 Introduction
- •4.2.2 Etiology
- •4.2.3 Histopathology
- •4.2.4 Nephroblastomatosis
- •4.2.5 Clinical Features
- •4.2.6 Risk Factors for Wilms’ Tumor
- •4.2.7 Staging of Wilms Tumor
- •4.2.8 Investigations
- •4.2.9 Prognosis and Complications of Wilms Tumor
- •4.2.10 Surgical Considerations
- •4.2.11 Surgical Complications
- •4.2.12 Prognosis and Outcome
- •4.2.13 Extrarenal Wilms’ Tumors
- •4.3 Mesoblastic Nephroma
- •4.3.1 Introduction
- •4.3.3 Epidemiology
- •4.3.5 Clinical Features
- •4.3.6 Investigations
- •4.3.7 Treatment and Prognosis
- •4.4 Clear Cell Sarcoma of the Kidney (CCSK)
- •4.4.1 Introduction
- •4.4.2 Pathophysiology
- •4.4.3 Clinical Features
- •4.4.4 Investigations
- •4.4.5 Histopathology
- •4.4.6 Treatment
- •4.4.7 Prognosis
- •4.5 Malignant Rhabdoid Tumor of the Kidney
- •4.5.1 Introduction
- •4.5.2 Etiology and Pathophysiology
- •4.5.3 Histologic Findings
- •4.5.4 Clinical Features
- •4.5.5 Investigations and Diagnosis
- •4.5.6 Treatment and Outcome
- •4.5.7 Mortality/Morbidity
- •4.6 Renal Cell Carcinoma in Children
- •4.6.1 Introduction
- •4.6.2 Histopathology
- •4.6.4 Staging
- •4.6.5 Clinical Features
- •4.6.6 Investigations
- •4.6.7 Management
- •4.6.8 Prognosis
- •4.7 Angiomyolipoma of the Kidney
- •4.7.1 Introduction
- •4.7.2 Histopathology
- •4.7.4 Clinical Features
- •4.7.5 Investigations
- •4.7.6 Treatment and Prognosis
- •4.8 Renal Lymphoma
- •4.8.1 Introduction
- •4.8.2 Etiology and Pathogenesis
- •4.8.3 Diagnosis
- •4.8.4 Clinical Features
- •4.8.5 Treatment and Prognosis
- •4.9 Ossifying Renal Tumor of Infancy
- •4.10 Metanephric Adenoma
- •4.10.1 Introduction
- •4.10.2 Histopathology
- •4.10.3 Diagnosis
- •4.10.4 Clinical Features
- •4.10.5 Treatment
- •4.11 Multilocular Cystic Renal Tumor
- •Further Reading
- •Wilms’ Tumor
- •Mesoblastic Nephroma
- •Renal Cell Carcinoma in Children
- •Angiomyolipoma of the Kidney
- •Renal Lymphoma
- •Ossifying Renal Tumor of Infancy
- •Metanephric Adenoma
- •Multilocular Cystic Renal Tumor
- •5.1 Introduction
- •5.2 Embryology
- •5.4 Histologic Findings
- •5.7 Associated Anomalies
- •5.8 Clinical Features
- •5.9 Investigations
- •5.10 Treatment
- •Further Reading
- •6: Congenital Ureteral Anomalies
- •6.1 Etiology
- •6.2 Clinical Features
- •6.3 Investigations and Diagnosis
- •6.4 Duplex (Duplicated) System
- •6.4.1 Introduction
- •6.4.3 Clinical Features
- •6.4.4 Investigations
- •6.4.5 Treatment and Prognosis
- •6.5 Ectopic Ureter
- •6.5.1 Introduction
- •6.5.3 Clinical Features
- •6.5.4 Diagnosis
- •6.5.5 Surgical Treatment
- •6.6 Ureterocele
- •6.6.1 Introduction
- •6.6.3 Clinical Features
- •6.6.4 Investigations and Diagnosis
- •6.6.5 Treatment
- •6.6.5.1 Surgical Interventions
- •6.8 Mega Ureter
- •Further Reading
- •7: Congenital Megaureter
- •7.1 Introduction
- •7.3 Etiology and Pathophysiology
- •7.4 Clinical Presentation
- •7.5 Investigations and Diagnosis
- •7.6 Treatment and Prognosis
- •7.7 Complications
- •Further Reading
- •8.1 Introduction
- •8.2 Pathophysiology
- •8.4 Etiology of VUR
- •8.5 Clinical Features
- •8.6 Investigations
- •8.7 Management
- •8.7.1 Medical Treatment of VUR
- •8.7.2 Antibiotics Used for Prophylaxis
- •8.7.3 Anticholinergics
- •8.7.4 Surveillance
- •8.8 Surgical Therapy of VUR
- •8.8.1 Indications for Surgical Interventions
- •8.8.2 Indications for Surgical Interventions Based on Age at Diagnosis and the Presence or Absence of Renal Lesions
- •8.8.3 Endoscopic Injection
- •8.8.4 Surgical Management
- •8.9 Mortality/Morbidity
- •Further Reading
- •9: Pediatric Urolithiasis
- •9.1 Introduction
- •9.2 Etiology
- •9.4 Clinical Features
- •9.5 Investigations
- •9.6 Complications of Urolithiasis
- •9.7 Management
- •Further Reading
- •10.1 Introduction
- •10.2 Embryology of Persistent Müllerian Duct Syndrome
- •10.3 Etiology and Inheritance of PMDS
- •10.5 Clinical Features
- •10.6 Treatment
- •10.7 Prognosis
- •Further Reading
- •11.1 Introduction
- •11.2 Physiology and Bladder Function
- •11.2.1 Micturition
- •11.3 Pathophysiological Changes of NBSD
- •11.4 Etiology and Clinical Features
- •11.5 Investigations and Diagnosis
- •11.7 Management
- •11.8 Clean Intermittent Catheterization
- •11.9 Anticholinergics
- •11.10 Botulinum Toxin Type A
- •11.11 Tricyclic Antidepressant Drugs
- •11.12 Surgical Management
- •Further Reading
- •12.1 Introduction
- •12.2 Etiology
- •12.3 Pathophysiology
- •12.4 Clinical Features
- •12.5 Investigations and Diagnosis
- •12.6 Management
- •Further Reading
- •13.1 Introduction
- •13.2 Embryology
- •13.3 Epispadias
- •13.3.1 Introduction
- •13.3.2 Etiology
- •13.3.4 Treatment
- •13.3.6 Female Epispadias
- •13.3.7 Surgical Repair of Female Epispadias
- •13.3.8 Prognosis
- •13.4 Bladder Exstrophy
- •13.4.1 Introduction
- •13.4.2 Associated Anomalies
- •13.4.3 Principles of Surgical Management of Bladder Exstrophy
- •13.4.4 Evaluation and Management
- •13.5 Cloacal Exstrophy
- •13.5.1 Introduction
- •13.5.2 Skeletal Changes in Cloacal Exstrophy
- •13.5.3 Etiology and Pathogenesis
- •13.5.4 Prenatal Diagnosis
- •13.5.5 Associated Anomalies
- •13.5.8 Surgical Reconstruction
- •13.5.9 Management of Urinary Incontinence
- •13.5.10 Prognosis
- •13.5.11 Complications
- •Further Reading
- •14.1 Introduction
- •14.2 Etiology
- •14.3 Clinical Features
- •14.4 Associated Anomalies
- •14.5 Diagnosis
- •14.6 Treatment and Prognosis
- •Further Reading
- •15: Cloacal Anomalies
- •15.1 Introduction
- •15.2 Associated Anomalies
- •15.4 Clinical Features
- •15.5 Investigations
- •Further Reading
- •16: Urachal Remnants
- •16.1 Introduction
- •16.2 Embryology
- •16.4 Clinical Features
- •16.5 Tumors and Urachal Remnants
- •16.6 Management
- •Further Reading
- •17: Inguinal Hernias and Hydroceles
- •17.1 Introduction
- •17.2 Inguinal Hernia
- •17.2.1 Incidence
- •17.2.2 Etiology
- •17.2.3 Clinical Features
- •17.2.4 Variants of Hernia
- •17.2.6 Treatment
- •17.2.7 Complications of Inguinal Herniotomy
- •17.3 Hydrocele
- •17.3.1 Embryology
- •17.3.3 Treatment
- •Further Reading
- •18: Cloacal Exstrophy
- •18.1 Introduction
- •18.2 Etiology and Pathogenesis
- •18.3 Associated Anomalies
- •18.4 Clinical Features and Management
- •Further Reading
- •19: Posterior Urethral Valve
- •19.1 Introduction
- •19.2 Embryology
- •19.3 Pathophysiology
- •19.5 Clinical Features
- •19.6 Investigations and Diagnosis
- •19.7 Management
- •19.8 Medications Used in Patients with PUV
- •19.10 Long-Term Outcomes
- •19.10.3 Bladder Dysfunction
- •19.10.4 Renal Transplantation
- •19.10.5 Fertility
- •Further Reading
- •20.1 Introduction
- •20.2 Embryology
- •20.4 Clinical Features
- •20.5 Investigations
- •20.6 Treatment
- •20.7 The Müllerian Duct Cyst
- •Further Reading
- •21: Hypospadias
- •21.1 Introduction
- •21.2 Effects of Hypospadias
- •21.3 Embryology
- •21.4 Etiology of Hypospadias
- •21.5 Associated Anomalies
- •21.7 Clinical Features of Hypospadias
- •21.8 Treatment
- •21.9 Urinary Diversion
- •21.10 Postoperative Complications
- •Further Reading
- •22: Male Circumcision
- •22.1 Introduction
- •22.2 Anatomy and Pathophysiology
- •22.3 History of Circumcision
- •22.4 Pain Management
- •22.5 Indications for Circumcision
- •22.6 Contraindications to Circumcision
- •22.7 Surgical Procedure
- •22.8 Complications of Circumcision
- •Further Reading
- •23: Priapism in Children
- •23.1 Introduction
- •23.2 Pathophysiology
- •23.3 Etiology
- •23.5 Clinical Features
- •23.6 Investigations
- •23.7 Management
- •23.8 Prognosis
- •23.9 Priapism and Sickle Cell Disease
- •23.9.1 Introduction
- •23.9.2 Epidemiology
- •23.9.4 Pathophysiology
- •23.9.5 Clinical Features
- •23.9.6 Treatment
- •23.9.7 Prevention of Stuttering Priapism
- •23.9.8 Complications of Priapism and Prognosis
- •Further Reading
- •24.1 Introduction
- •24.2 Embryology and Normal Testicular Development and Descent
- •24.4 Causes of Undescended Testes and Risk Factors
- •24.5 Histopathology
- •24.7 Clinical Features and Diagnosis
- •24.8 Treatment
- •24.8.1 Success of Surgical Treatment
- •24.9 Complications of Orchidopexy
- •24.10 Infertility and Undescended Testes
- •24.11 Undescended Testes and the Risk of Cancer
- •Further Reading
- •25: Varicocele
- •25.1 Introduction
- •25.2 Etiology
- •25.3 Pathophysiology
- •25.4 Grading of Varicoceles
- •25.5 Clinical Features
- •25.6 Diagnosis
- •25.7 Treatment
- •25.8 Postoperative Complications
- •25.9 Prognosis
- •Further Reading
- •26.1 Introduction
- •26.2 Etiology and Risk Factors
- •26.3 Diagnosis
- •26.4 Intermittent Testicular Torsion
- •26.6 Effects of Testicular Torsion
- •26.7 Clinical Features
- •26.8 Treatment
- •26.9.1 Introduction
- •26.9.2 Etiology of Extravaginal Torsion
- •26.9.3 Clinical Features
- •26.9.4 Treatment
- •26.10 Torsion of the Testicular or Epididymal Appendage
- •26.10.1 Introduction
- •26.10.2 Embryology
- •26.10.3 Clinical Features
- •26.10.4 Investigations and Treatment
- •Further Reading
- •27: Testicular Tumors in Children
- •27.1 Introduction
- •27.4 Etiology of Testicular Tumors
- •27.5 Clinical Features
- •27.6 Staging
- •27.6.1 Regional Lymph Node Staging
- •27.7 Investigations
- •27.8 Treatment
- •27.9 Yolk Sac Tumor
- •27.10 Teratoma
- •27.11 Mixed Germ Cell Tumor
- •27.12 Stromal Tumors
- •27.13 Simple Testicular Cyst
- •27.14 Epidermoid Cysts
- •27.15 Testicular Microlithiasis (TM)
- •27.16 Gonadoblastoma
- •27.17 Cystic Dysplasia of the Testes
- •27.18 Leukemia and Lymphoma
- •27.19 Paratesticular Rhabdomyosarcoma
- •27.20 Prognosis and Outcome
- •Further Reading
- •28: Splenogonadal Fusion
- •28.1 Introduction
- •28.2 Etiology
- •28.4 Associated Anomalies
- •28.5 Clinical Features
- •28.6 Investigations
- •28.7 Treatment
- •Further Reading
- •29: Acute Scrotum
- •29.1 Introduction
- •29.2 Torsion of Testes
- •29.2.1 Introduction
- •29.2.3 Etiology
- •29.2.4 Clinical Features
- •29.2.5 Effects of Torsion of Testes
- •29.2.6 Investigations
- •29.2.7 Treatment
- •29.3 Torsion of the Testicular or Epididymal Appendage
- •29.3.1 Introduction
- •29.3.2 Embryology
- •29.3.3 Clinical Features
- •29.3.4 Investigations and Treatment
- •29.4.1 Introduction
- •29.4.2 Etiology
- •29.4.3 Clinical Features
- •29.4.4 Investigations and Treatment
- •29.5 Idiopathic Scrotal Edema
- •29.6 Testicular Trauma
- •29.7 Other Causes of Acute Scrotum
- •29.8 Splenogonadal Fusion
- •Further Reading
- •30.1 Introduction
- •30.2 Imperforate Hymen
- •30.3 Vaginal Atresia
- •30.5 Associated Anomalies
- •30.6 Embryology
- •30.7 Clinical Features
- •30.8 Investigations
- •30.9 Management
- •Further Reading
- •31: Disorders of Sexual Development
- •31.1 Introduction
- •31.2 Embryology
- •31.3 Sexual and Gonadal Differentiation
- •31.5 Evaluation of a Newborn with DSD
- •31.6 Diagnosis and Investigations
- •31.7 Management of Patients with DSD
- •31.8 Surgical Corrections of DSD
- •31.9 Congenital Adrenal Hyperplasia (CAH)
- •31.10 Androgen Insensitivity Syndrome (Testicular Feminization Syndrome)
- •31.13 Gonadal Dysgenesis
- •31.15 Ovotestis Disorders of Sexual Development
- •31.16 Other Rare Disorders of Sexual Development
- •Further Reading
- •Index
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4.3Mesoblastic Nephroma
4.3.1Introduction
•Mesoblastic nephroma is also called congenital mesoblastic nephroma (CMN) or fetal renal hamartoma.
•This tumor was first described as a separate entity by Bolande et al. in 1967.
•Prior to this, it was erroneously confused with congenital Wilms tumor.
•Congenital mesoblastic nephroma (or simply mesoblastic nephroma) represents 3–10 % of all pediatric renal tumors.
•It is called congenital because it can be diagnosed in utero by ultrasound or within the first 3 months of life.
•Approximately 50 % occur during the neonatal period and 80 % of cases are reported within the first month of life.
•Congenital mesoblastic nephroma represents 3–10 % of all pediatric renal tumors. It was initially confused with congenital Wilms’ tumor.
•Mesoblastic nephroma is the most common renal tumor identified in the neonatal period and the most frequent benign renal tumor in childhood.
•Mesoblastic nephroma is most commonly diagnosed in the first 3 months of life.
•About 90 % present in the first year of life, 50–75 % of cases occur in young infants, and almost none occur after the age of 3 years.
•It is more common in males than females.
•The tumor is considered a hamartoma.
•It is presumed to originate from proliferating nephrogenic mesenchyme.
•Congenital mesoblastic nephroma is almost always unilateral and is rarely malignant.
•It may extend beyond the renal capsule, but rarely metastasizes to distant organs.
•Metastases to distant organs such as the brain, bone, and lungs have been reported.
•Commonly, mesoblastic nephroma appear as a large, solitary, predominantly solid, coarse, and echogenic renal mass that may contain cystic areas.
•Congenital renal tumors comprise 2.5–7 % of all perinatal tumors.
•Congenital renal neoplasms include, in decreasing order of frequency:
–Congenital mesoblastic nephroma
–Wilms tumor
–Rhabdoid tumor of the kidney
–Clear cell sarcoma
–Hamartomas
–Ossifying tumor of infancy
•The Diagnosis is usually made in the antenatal period or immediately after birth.
•Mesoblastic nephroma is considered generally a benign renal tumor.
•Among the renal tumors:
–Wilms tumor is the most common renal tumor, accounting for 80–85 % of all pediatric renal tumors.
–Congenital mesoblastic nephroma accounts for about 10–15 % of all pediatric renal tumors
–Rhabdoid tumor of the kidney accounts for 5–10 % of all pediatric renal tumors.
–Clear cell sarcoma (CCSK) accounts for 5–10 % of all pediatric renal tumors.
•The differential diagnosis based on age at presentation and includes the following tumors:
– Mesoblastic nephroma: from birth to
1year.
–Rhabdoid tumor: from 1 to 2 years of age.
–Clear cell sarcoma of the kidney: from 2 to
3years of age.
–Wilm’s tumor: over 3 years of age (Mean 3.5 years).
•There is an association between CMN and:
–Polyhyramnios with or without hydrops fetalis
–Hypertension
–Prematurity
–Some mesoblastic nephromas are associated with paraneoplastic syndromes such as:
• Hypertension: This is secondary to increased secretion of renin (hyperreninemia).
• Hypercalcemia: This is due to prostaglandin secretion from the tumor cells.
•Congenital mesoblastic nephroma arises from renal mesenchyma and is usually benign.
•Although CMN is considered a benign tumor, it could behave aggressively.
4.3 Mesoblastic Nephroma |
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•The tumor lacks renal blastema and neoplastic metanephric elements, thereby differentiating it from Wilms tumor.
•In addition, it tends to infiltrate the kidney, rather than form the pseudocapsule of classic Wilms tumor.
•Congenital mesoblastic nephroma is almost always unilateral.
•It may extend beyond the renal capsule, but rarely metastasizes to distant organs.
4.3.2Classification
•Mesoblastic nephroma is a mesenchymal tumor.
•Macroscopically the tumor is a solid unencapsulated mass which often occurs near the renal hilum.
•It tends to invade the surrounding structures and renal parenchyma.
•Haemorrhage and necrosis are infrequent.
•Histologically, it is typically composed of connective tissue growing between nephrons, usually replacing most of the renal parenchyma.
•The classic cytological description of the lesion is that of cellular clusters of spindle cells, mild nuclear pleomorphism, mitotic activity and no blastema.
•Pathologically, mesoblastic nephroma are divided into two types:
–The classic variant
–The cellular variants
•The two types differ in the age at presentation, histologic characteristics, imaging characteristics and the biologic behavior of the tumors.
•The classic variant:
–This presents earlier, usually before age 3 months.
–It usually presents as a solid mass with small foci of necrosis or hemorrhage.
–It does not invade the perinephric tissues or the vascular pedicle.
–It is associated with an excellent outcome after complete surgical resection of the tumor.
–On gross examination, the tumor:
•Is noncapsulated
•Has a whorled trabeculated appearance
similar to leiomyomas, hence the name leiomyomatous hamartoma of the kidney.
–Histologically:
•It consists of uniform spindle cells arranged in bundles with scattered foci of entrapped normal glomeruli and tubules.
•The cellular variant:
–This type presents later, usually after age 3 months.
–More heterogeneous in appearance on imaging
–Tends to be larger and presents later in infancy
–May exhibit aggressive behavior including vascular encasement and metastasis
–It demonstrates more aggressive imaging characteristics, with larger areas of necrosis and hemorrhage.
–It may invade the perinephric fat and connective tissues.
–It is associated with a higher rate of local recurrence and metastatic disease.
–On gross examination:
•The tumor is fleshy with multiple foci of necrosis, cystic change, and hemorrhage.
–Histologically:
•It consists of spindle cells arranged in a haphazard sheets with a limited tendency to form bundles as seen in the classic form.
–The cellular variant may also demonstrate the t(12;15) translocation, which is diagnostic.
–On reverse-transcription polymerase chain reaction (RT-PCR), it may demonstrate the ETV6-NTRK3 gene fusion, a feature also seen in congenital infantile fibrosarcoma, hence the name infantile fibrosarcoma of the kidney.
•Factors that increase the risk of recurrence and metastasis include:
–Cellular variant
–Older age at presentation
–Positive surgical resection margins
•Metastases to distant organs such as the brain,
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4 Renal Tumors in Children |
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bone, and lungs have been reported. These are seen in cellular variant.
•The cellular variant has been shown to bear the t(12;15)(p13;q25) and ETV6 (chromosome 12)-NTRK3 (chromosome 15) gene fusion. These combined genes are thought to activate tyrosine kinase growth signaling. This gene fusion transcript is also reported in congenital or infantile fibrosarcoma
4.3.3Epidemiology
•Mesoblastic nephroma is the most common renal tumor in neonates and infants and represents 3–10 % of the pediatric renal tumors.
•Mesoblastic nephroma is the most common renal tumor presenting in the neonatal period and accounts for approximately 54 % of tumors in this age group.
•It was initially described as a benign tumor, but currently a spectrum of mesoblastic nephroma exists:
–The classic type representing the benign disease
–The cellular variant representing the aggressive disease (40–60 %)
–The mixed tumors falling somewhere in the middle.
–Mesoblastic nephroma has a slight male predominance, with a male-to-female ratio of 1.5:1.
–Histologically, the classic form is characterized by rare mitoses and absence of necrosis. Entrapped tubules and/or glomeruli are usually seen at the periphery of the tumor.
–Atypical or cellular variant is characterized by a high mitotic index, hypercellularity, and an atypical growth pattern with necrosis, hemorrhage, and invasion of adjacent structures.
4.3.4Histopathology (Figs. 4.69 and 4.70)
•Mesoblastic nephroma is a solid tumor and mostly these tumors are located near the hilum of the kidney and may extensively involve the renal sinus.
•Cysts are rarely seen but there may be hemorrhage and necrosis.
•The tumor is usually well circumscribed, but it may be seen infiltrating the renal parenchyma and even the perirenal fat.
•The cut surface of the tumor specimen shows a yellow-tan tumor with a “whorled” appearance that is similar to a uterine leiomyoma with spindled cell bundles.
•It is composed of immature renal stromal cells.
•The tumor lacks renal blastema and neoplastic metanephric elements, thereby differentiating it from Wilms tumor.
Figs. 4.69 and 4.70 Clinical photograph of a resected mesoblastic nephroma. Note the whorled appearance of the tumor. Note also the normal kidney tissue. Note that
the normal kidney is infiltrated by the tumor and not compressed like Wilms’ tumor. Note also the absence of a capsule
4.3 Mesoblastic Nephroma |
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•The tumor tends to infiltrate the kidney, rather than form the pseudocapsule of classic Wilms tumor.
•There are two pathologic variants of mesoblastic nephroma:
–Classic
–Atypical or cellular.
•The classic type is characterized by rare mitoses and absence of necrosis. Entrapped tubules and/or glomeruli are usually seen at the periphery of the tumor.
•Classic mesoplastic nephroma:
–Fascicles and whorls of spindly cells.
–These cells have the features of secondary mesenchyme, which, in contrast with those of primary mesenchyme (mesoblast), lack the capacity to form epithelial structures.
–Instead, the proliferating cells acquire the features of fibroblasts, myofibroblasts, or smooth muscle cells.
–These cells contain vimentin, fibronectin, and sometimes actin, but not keratin or laminin.
–The tumor has irregular borders, with bands of tumor extending into surrounding soft tissue.
–It also permeates the adjacent renal parenchyma to encircle groups of tubules and glomeruli.
–Metaplastic tissues are usually found at the tumor-kidney interface or near entrapped renal tubules and glomeruli, most commonly cartilage.
–Extramedullary hematopoiesis and cuboidal metaplasia may also be present.
–Mitotic figures may be encountered, but frequent mitoses are more characteristically seen in cellular mesoblastic nephroma.
•Atypical or cellular variant is characterized by:
–A high mitotic index.
–Hypercellularity.
–An atypical growth pattern with necrosis, hemorrhage, and invasion of adjacent structures.
–The cellular type accounts for 40–60 % of mesoblastic nephroma cases.
•Cellular mesoblastic nephroma:
–This is more cellular than the classical type and has a sarcomatous appearance consisting of tightly packed cells with frequent mitoses (25–30/10 HPF).
–Data from the National Wilms Tumor Study show that cellular mesoblastic nephroma is commoner than classic mesoblastic nephroma with a ratio of 3:1.
–Cellular mesoblastic nephroma presents a few months later in life than the classic mesoblastic nephroma.
–Unlike the classic type, cellular mesoblastic nephroma may reach a huge size and can weigh more than 1 kg (Fig. 4.71).
–Histologically, two types of cells are seen. The more common cell type is a plump cell with ample cytoplasm and a vesicular nucleus. The less common type is a blue cell, which shows less cytoplasm and resembles cells of infantile fibrosarcoma.
•The cellular variant has been shown to bear the t (12; 15) (p13; q25) and ETV6 (chromosome 12)-NTRK3 (chromosome 15) gene fusion. These combined genes are thought to activate tyrosine kinase growth signaling. This gene fusion transcript is also reported in congenital or infantile fibrosarcoma.
Fig. 4.71 A clinical photograph showing an excised large mesoblastic nephroma that weighed more than one kilogram