perivascular epithelioid cell tumors ( pecomas ) are a rare group of mesenchymal neoplasms composed of distinctive cells which show a focal association with the walls of blood vessels and usually express melanocytic and smooth - muscle markers .
these tumors include renal angiomyolipoma , lymphangioleiomyomatosis , clear cell sugar tumor of the lung , and similar neoplasms occurring in the retroperitoneum , kidney , uterus , pancreas , or other visceral and soft - tissue sites .
imaging findings of these tumors are usually nonspecific . to our knowledge , in the english literature , there are only two publications referring to pecomas with perirenal manifestation with no report on computed tomography ( ct ) findings .
we examined the case of a 44-year - old woman who presented with left lumbar pain of 4 months duration .
sonography revealed the presence of a large , heterogenous , well - margined mass , located in the left perirenal space [ figure 1a ] .
the lesion was partly cystic solid , with solid components detected with moderate vascularity at doppler examination [ figure 1b ] .
the presence of a large , inhomogeneous left perirenal mass [ figure 2a ] , in close proximity to the renal capsule was confirmed .
the dimensions of the lesion were 6 cm  7 cm  10 cm , approximately .
the tumor had cystic parts , with ct density similar to that of water , not enhancing after intravenous contrast medium administration , and solid parts , with strong , heterogeneous enhancement [ figure 2b ] .
peritumoral vascularity , seen as asymmetrically increased vessels adjacent to the mass within gerota fascia , was also identified [ figure 2c ] .
mass effect to the surrounding organs was noted , particularly to the left kidney , without obvious findings of invasion .
44-year - old woman with 4-month history of lumbar pain diagnosed with perivascular epithelioid cell tumor .
( a ) sagittal sonographic image of the left hypochondrium depicts the presence of a large heterogenous left perirenal mass .
the lesion has cystic parts ( asterisk ) and solid , heterogeneous components ( long arrow ) .
( b ) sagittal power doppler image of the left perirenal mass reveals vascularity of the solid parts ( arrowheads ) .
44-year - old woman with 4-month history of lumbar pain diagnosed with perivascular epithelioid cell tumor .
( a ) transverse noncontrast computed tomography image demonstrates inhomogeneous solid parts of the lesion ( arrow ) .
the mean computed tomography density of the solid components is 35 hu on unenhanced images , similar to that of normal renal parenchyma .
coronal reformations during ( b ) the portal phase and ( c ) the excretory phase depict sharply demarcated left perinephric mass ( arrow ) , partly cystic and solid , in close proximity to the renal capsule .
the solid parts of the tumor enhance intensely and heterogeneously , with a mean portal phase attenuation of 100 hu .
prominent vessels are seen in the left perirenal space adjacent to the lesion ( long arrow ) .
intraoperatively , the mass was separated from the renal capsule by a thin layer of fibrous tissue and tumorectomy was performed .
histologically , the neoplasm was composed of spindle and epithelioid cells , immunoreactive for vimentin , desmin , smooth muscle actin , hmb45 , cd56 , cd99 , b cell lymphoma-2 , er , nse , and focally for mart-1 and cd31 .
areas of myxoid , partly cystic degeneration and areas of hemorrhage were identified within the tumor .
overall , the findings were consistent with the diagnosis of pecoma of uncertain malignant potential .
the patient had an uneventful recovery and was advised to return for follow - up , 3 months after the operation .
the category  pecoma  was first suggested in 1992 by bonetti and includes neoplasm primarily composed of hmb-45-positive epithelioid cells with a perivascular distribution .
however , a minority shows aggressive behavior , with local recurrence and/or distant metastases , more often in lungs , liver , and peritoneum .
malignant pecomas have been reported to be associated with two or more of the following risk factors : size > 5 cm , high nuclear grade and cellularity , mitotic rate > 1 mitosis / hpf , and presence of necrosis or vascular invasion .
tan et al . in a retrospective analysis of 32 pecomas reported a mean tumor diameter of 5.1 cm , well - defined margins , hypodensity on ct , low and high signal intensity on t1- and t2-weighted magnetic resonance imaging ( mri ) images , respectively , and strong , heterogeneous enhancement .
tirumani et al . , in a retrospective study of 36 malignant pecomas reported large , well - circumscribed masses , heterogeneous on sonography , with ct density and signal intensity on t1-weighted images similar to that of skeletal muscles , heterogeneity on t2-weighted images and inhomogeneous enhancement .
approximately , 100 cases of pecomas have been reported up to date in the literature , most commonly involving the genitourinary tract , two of them with perirenal location . di blasi et al . reported a case of renal capsuloma observed as an incidental finding , coexisting with a papillary transitional cell carcinoma of the pelvicaliceal system .
the second case of perirenal pecoma was reported on a 57-year - old woman by gunia et al .
the authors described the mri findings of this entity , as a predominantly solid mass , with occasional cystic changes .
the tumor was mainly hypointense on t1 and fat - suppressed t2-weighted images , when compared to normal renal parenchyma , with delayed contrast enhancement .
the ct findings of pecoma with perirenal manifestation have never been reported in the english literature . in our patient ,
a well - defined , inhomogeneous perirenal mass was detected , with cystic parts and solid components , the latter heterogeneously enhancing after contrast material administration .
a variety of neoplastic and proliferative disorders may affect the perirenal space , with a wide array of cross - sectional imaging findings . in cases of solitary partly cystic - solid masses of the perirenal space ,
differential diagnosis should include the following : leiomyoma , hemangiopericytoma , malignant fibrous histiocytoma , hemangioma and more rarely leukemia , primary extragastrointestinal stromal tumor , and castleman 's disease .
perirenal leiomyoma represents a rare benign mesenchymal neoplasm , arising from the renal capsule and extending into the perirenal space .
imaging findings include a well - demarcated soft - tissue mass that is supplied by renal capsular vessels .
large leiomyomas are usually heterogeneous , due to the presence of hemorrhage and/or cystic myxoid degeneration .
hemangiopericytoma represents a rare retroperitoneal soft tissue neoplasm , more often detected as large , lobulated , well - defined , hypervascular soft tissue mass with areas of calcification and necrosis .
it is usually detected as a large heterogeneous mass , displacing the kidney , with areas of necrosis and hemorrhage .
perirenal hemangioma is an extremely rare benign mesenchymal renal tumor , with nonspecific imaging features .
however , the depiction of a soft tissue mass with phleboliths , hyperintensity on t2-weighted mri images , and delayed or persistent enhancement are considered as suggestive of the diagnosis . isolated leukemic involvement and primary extragastrointestinal stromal tumor with perirenal location are extremely rare , with nonspecific imaging findings .
isolated perirenal lesions in castelman disease are also rare , detected as homogeneous soft tissue masses , with well - defined margins .
however , in the presence of a large , well - defined perirenal mass , partly cystic - solid , with solid components enhancing after contrast material administration , accompanied by peritumoral vessels , this rare entity should be included in the differential diagnosis .
 the world health organization defines perivascular epithelioid cell tumors ( pecomas ) as mesenchymal tumors and tumor - like conditions composed of epithelioid cells with a perivascular distribution . 
 these tumors may show benign or malignant histology and/or biological behavior . 
 however , the pathological features of malignancy may not correlate with biologic aggressiveness , and the criteria for malignancy are not clearly defined . 
 abdominopelvic pecomas are very rare and have been reported in various locations , including kidney , liver , pancreas , gastrointestinal tract , genitourinary tract , peritoneum , and retroperitoneum . 
 cross - sectional imaging techniques , including computed tomography ( ct ) may play an important role in the accurate detection and characterization of these tumors . 
 we present the third case of an extremely rare pecoma with perirenal location , discuss ct findings and differential diagnosis . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION
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