Mathew C. Raynor, MD
Raj S. Pruthi, MD, FACS
BASICS
DESCRIPTION
• Predominantly mesenchymal neoplasms arising from the renal capsule encompassing a wide variety of cell progenitors
– Tumors can be composed of fibrous, smooth muscle, vascular, adipose, nerve, or other tissue differentiation
Encompasses benign and malignant neoplasms
EPIDEMIOLOGY
Incidence
• Very rare tumors
• Represent up to ∼1.5% of all surgically treated benign renal masses (1)
• Incidentally found at autopsy in up to ∼5% of cases (1)
• Similar gender preference
Prevalence
Unknown, due to rarity of tumor
RISK FACTORS
• None known
– Increased cross-sectional imaging use may identify incidental mass
Genetics
• No recognized genetic predisposition
• Some common genetic alterations seen in soft tissue sarcomas
– No current clinical application for genetic alterations
PATHOPHYSIOLOGY
• Benign
– Leiomyoma, hemangiopericytoma, hemangioma, lymphangioma, myxoma, schwannoma, solitary fibrous tumor, paraganglioma, lipoma, fibroma, myolipoma
• Malignant
– Leiomyosarcoma, malignant fibrous histiocytoma, fibromyxoid sarcoma, hemangiosarcoma, liposarcoma, fibrosarcoma
ASSOCIATED CONDITIONS
Some renal hemangiomas may be associated with Sturge–Weber or Klippel–Trénaunay syndromes (1)
GENERAL PREVENTION
No preventive strategies identified
DIAGNOSIS
HISTORY
• Usually asymptomatic or discovered incidentally
• May present with hematuria or flank pain
• Weight loss, anorexia, malaise, or bone pain may signify metastatic disease
PHYSICAL EXAM
• Usually normal
– Rarely, flank mass may be palpable
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Urinalysis
– Microscopic hematuria may be identified, but usually normal
• CBC
– Anemia may be present with advanced disease or bleeding mass
• Serum chemistries usually normal
Imaging
• CT or MRI with and without contrast
– May show enhancing mass arising from the kidney
Indistinguishable from renal cell carcinoma in most cases
Presence of fat may signify angiomyolipoma, lipoma, or liposarcoma
• Chest x-ray
– Evaluate for metastatic disease
Diagnostic Procedures/Surgery
• Core needle biopsy
– May be used in cases of suspected renal malignancy or if active surveillance considered
• Angiography
– May be utilized for bleeding lesions
– Benign lesions usually hypovascular
Except hemangiopericytoma, which is highly vascular
Pathologic Findings
• Leiomyoma
– Firm, well-circumscribed, exophytic mass
– Microscopically, composed of spindle cells arranged in fascicles typical of smooth muscle
– Immunostaining positive for desmin, smooth muscle actin, and usually HMB-45 (1)[C]
• Hemangiopericytoma
– Solid, encapsulated mass
– Microscopically, varied cell shapes and sizes with morphologic variability
– Immunostaining positive for vimentin, BCL2, CD99 and negative for S100, cytokeratins, and HMB-45 (2)[C]
• Lymphangioma
– Well-encapsulated, multilocular cystic mass
– Microscopically, communicating cysts seen with flattened endothelial cells
– Immunostaining positive for D2-40
Labels lymphatic endothelium (1,3)[C]
• Solitary fibrous tumor
– Well-encapsulated firm mass without necrosis, cysts, or hemorrhage
– Microscopically, usually shows areas of spindle cells intermixed with hypocellular areas of fibrous tissue
– Immunostaining strongly positive for CD34
May also stain positive for CD99 and BCL2 and can be misclassified as hemangiopericytoma (1,2)[C]
• Leiomyosarcoma
– Usually large circumscribed mass with areas of necrosis
– Microscopically, spindle cells with haphazard growth pattern, nuclear pleomorphism, mitoses, and necrosis
– Immunostaining positive for SMA, desmin, and calponin (1)[C]
• Fibrosarcoma
– Large encapsulated mass
– Microscopically, elongated spindle cells
“Herringbone” pattern
– Immunostaining positive for vimentin
Differentiates fibrosarcoma from sarcomatoid RCC and leiomyosarcoma (1)[C]
• Malignant fibrous histiocytoma
– Solid, well-encapsulated mass
– Microscopically, proliferation of fibrohistiocytes
– Immunostaining positive for α1-antitrypsin and vimentin
DIFFERENTIAL DIAGNOSIS
• Angiomyolipoma
• Renal cysts
• Cystic nephroma
• Hemorrhagic/proteinaceous cysts
• Juxtaglomerular cell tumor
• Metastasis to kidney
• Oncocytoma
• Renal cell carcinoma
• Renal pseudotumor/scar
• Splenule (ectopic or traumatic)
• Urothelial carcinoma
• Wilms tumor
• Xanthogranulomatous pyelonephritis
TREATMENT
GENERAL MEASURES
• Surgical excision is both diagnostic and therapeutic
• Multimodal therapy generally recommended for malignancies such as sarcoma
MEDICATION
First Line
• Chemotherapy may be beneficial for certain advanced renal capsular malignancies (sarcoma) and metastatic lesions (4)[C].
– Usually given in the adjuvant setting.
• Targeted therapies may be beneficial in certain cases.
– Sunitinib, sorafenib, bevacizumab active in angiosarcoma, solitary fibrous tumor, and hemangiopericytoma.
SURGERY/OTHER PROCEDURES
• Surgical excision remains gold standard
– Radical nephrectomy
Open or minimally invasive
– Partial nephrectomy
Open or minimally invasive
Renal capsule margin should be excised with mass
Should be procedure of choice for patients with chronic kidney disease, when feasible
• Active surveillance
– Similar surveillance protocol for patients with small renal masses
ADDITIONAL TREATMENT
Radiation Therapy
• May be beneficial in cases of renal capsular sarcoma
– Usually given in adjuvant setting
Additional Therapies
Angioembolization for bleeding masses
Complementary & Alternative Therapies
None known
ONGOING CARE
PROGNOSIS
• Surgical excision usually curative
• Renal capsular sarcoma has poor prognosis
– Locally advanced disease is common
– Recurrence and metastases common
– Overall prognosis is poor, despite adjuvant chemoradiation
5-yr overall survival ∼15%
Median survival 28 mo (4)[C]
COMPLICATIONS
• Injury to adjacent organs
• Thromboembolic event
• Delayed bleed
– AV fistula
– Pseudoaneurysm
• Development of metastatic disease
FOLLOW-UP
Patient Monitoring
• Periodic surveillance imaging
• Serum chemistry panel and liver function tests
Patient Resources
None due to rarity of disease
REFERENCES
1. Katabathina VS, Vikram R, Nagar AM, et al. Mesenchymal neoplasms of the kidney in adults: Imaging spectrum with radiologic-pathologic correlation. Radiographics. 2010;30(6):1525–1540.
2. Brescia A, Pinto F, Gardi M, et al. Renal hemangiopericytoma: Case report and review of the literature. Urology. 2008;71(4):755.e9–e12.
3. Kalof AN, Cooper K. D2-40 immunohisto-chemistry—so far! Adv Anat Pathol. 2009;16(1):62–64.
4. Wang X, Xu R, Yan L, et al. Adult renal sarcoma: Clinical features and survival in a series of patients treated at a high-volume institution. Urology. 2011;77(4):836–841.
ADDITIONAL READING
• MacLennan GT, Cheng L. Neoplasms of the kidney. In: Bostwick DG, Cheng L, eds. Urologic Surgical Pathology. 2nd ed. Philadelphia, PA: Mosby Elsevier; 2008:104–106.
• Soft Tissue Sarcoma. NCCN Clinical Practice Guidelines in Oncology (www.nccn.org).
See Also (Topic, Algorithm, Media)
• Hemorrhage, Retroperitoneal and Perinephric
• Renal Capsular Neoplasms Image 
• Renal Mass
• Renal Masses, Benign WHO Classification
• Renal Sarcoma, Adult and Pediatric
CODES
ICD9
• 189.0 Malignant neoplasm of kidney, except pelvis
• 223.0 Benign neoplasm of kidney, except pelvis
• 239.5 Neoplasm of unspecified nature of other genitourinary organs
ICD10
• C64.9 Malignant neoplasm of unsp kidney, except renal pelvis
• D30.00 Benign neoplasm of unspecified kidney
• D49.5 Neoplasm of unspecified behavior of other genitourinary organs
CLINICAL/SURGICAL PEARLS
• Renal capsular neoplasms difficult to distinguish from RCC by imaging alone.
• Surgical excision (partial or radical nephrectomy) can be diagnostic and curative in most cases.
• Renal capsular sarcomas carry generally poor prognosis, despite adjuvant therapy.