To the Editor.-Multilocular cystic renal cell carcinoma (MCRCC) is a distinct subtype of clear cell renal cell carcinoma (RCC) thought to be derived from proximal tubular epithelium. These tumors are a rare entity, comprising approximately 1% to 2% of all renal tumors, and appear to have a favorable biology.1,2 We report a case of a 41-year-old woman who presented with the complaints of a dragging sensation and a mass in the left loin. Computed tomography showed a well-defined smooth, marginated, predominantly cystic mass lesion occupying the lower pole of the kidney. A left nephrectomy was performed. On gross examination, the specimen measured 12 � 9 � 7 cm, including a large cystic mass measuring 9 � 5 � 5 cm that occupied the lower renal pole. The cut section showed multiloculation with cysts ranging from 0.5 to 2 cm in diameter and filled with mucoid fluid and blood clots (Figure 1). Microscopy showed a multicystic tumor consisting of numerous cystic spaces filled with blood and septa lined by clear cells. These cells showed mild anisonucleosis and inconspicuous nucleoli confirming Fuhrman nuclear grade I (Figures 2 through 4). Renal capsule, vessels, and perinephric fat were free of tumor. A diagnosis of MCRCC, T2N0M0 according to the tumornode- metastasis system of staging, was made. A postoperative period of 1 year has lapsed and the patient has not reported to the hospital with any further complaints.
The 2004 World Health Organization classification of kidney tumors recognizes MCRCC as a rare variant of clear cell RCC with a favorable biology.3 Although cysts are common in clear cell renal cell carcinoma, only rarely is the tumor entirely composed of cysts. MCRCC is a rare entity, comprising approximately 1% to 2% of all renal tumors.2
The term MCRCC should be used exclusively to identify cystic RCC with a small volume (25% or less) of neoplastic clear cells in the cyst wall.4 Diagnostic criteria for MCRCC were defined by the 2004 World Health Organization classification of kidney tumors based on previous reports and the suggestions of Eble and Bonsib.3,5 Four mechanisms have been described to account for renal cell carcinomas with cystic features: intrinsic unilocular cystic growth (papillary cystic adenocarcinoma), intrinsic multilocular cystic growth, tumor necrosis resulting in cyst formation (pseudocyst), and tumor arising in a preexisting simple renal cyst.1
The differential diagnosis of a multilocular cystic renal mass includes numerous cystic diseases of the kidney. Most of these are excluded on computed tomography findings, except a benign entity known as multilocular cystic nephroma, which requires microscopic analysis for differentiation. Microscopically, multilocular cystic nephroma demonstrates multilocular cysts lined by a single layer of flattened, low, cuboidal epithelium with eosinophilic cytoplasm and no nuclear atypia. The fibrous septa within the cyst wall are cellular, resembling ovarian stroma, and may contain mature tubules. Cystic nephroma in adults is considered to belong to the spectrum of cystic renal lesions, ranging from typical cystic nephroma to mixed epithelial and stromal tumor of the kidney.6
Clinically, MCRCC behaves as a low-grade variant of RCC with stage I disease at initial presentation in 83% to 88% of cases.2 The tumor has an extremely high cure rate following surgical resection, with a range of 92% to 100% at a mean follow-up period of 5 to 6 years.7 Vascular invasion, sarcomatous transformation, and metastatic spread have not been reported.
The diagnostic rarity of finding a completely cystic renal cell carcinoma and the excellent prognosis of MCRCC compared with the other variants of RCC differentiate it, and few authors have suggested renaming it as multilocular cystic renal cell neoplasmof low malignant potential.7
[Reference]
1. Murphy WM, Grignon DJ, Perlman EJ. Kidney tumors in adults. In: Tumors of the Kidney, Bladder, and Related Urinary Structures. Washington, DC: American Registry of Pathology; 2004: 121-123. AFIP Atlas of Tumor Pathology; 4th series, fascicle 1.
2. Shah V, Pathak H. Multilocular cystic renal cell carcinoma: a report of two cases with a rare feature. Internet J Urol. 2010:6(2). http://www. ispub.com/journal/the_internet_journal_of_urology/ volume_6_number_2_41/article/multilocular-cysticrenal- cell-carcinoma-a-report-of-two-cases-with-arare- feature.html. Accessed August 25, 2010.
3. Eble JN, Bonsib SM. Extensively cystic renal neoplasms: cystic nephroma, cystic partially differentiated nephroblastoma, multilocular cystic renal cell carcinoma and cystic hamartoma of renal pelvis. Semin Diagn Pathol. 1998;15(1): 2-20.
4. Nassir A, Jollimore J, Gupta R, Bell D, Norman R. Multilocular cystic renal cell carcinoma: a series of 12 cases and review of the literature. Urology. 2002;60(3):421-427.
5. Fletcher CDM. Diagnostic Histopathology of Tumors. 3rd ed. Philadelphia, PA: Churchill Livingstone Elsevier; 2007:491-492.
6. Antic T, Perry KT, Harrison K, et al. Mixed epithelial and stromal tumor of the kidney and cystic nephroma share overlapping features: reappraisal of 15 lesions. Arch Pathol Lab Med. 2006; 130(1):80-85.
7. Suzigan S, L�pez-Beltr�n A, Montironi R et al. Multilocular cystic renal cell carcinoma: a report of 45 cases of a kidney tumor of low malignant potential. Am J Clin Pathol. 2006;125(2):217-222.
The author has no relevant financial interest in the products or companies described in this article.
[Author Affiliation]
SHWETA AGARWAL, DCP, DNB
Institute of Pathology
ICMR
Safdarjung Hospital Campus
New Delhi, India
USHA AGRAWAL, MD
Institute of Pathology
ICMR
Safdarjung Hospital Campus
New Delhi, India
N. K. MOHANTY, MCh
Department of Urology
Safdarjung Hospital
New Delhi, India
SUNITA SAXENA, DCP, MD
Institute of Pathology
ICMR
Safdarjung Hospital Campus
New Delhi, India
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