|ECR 2019 / C-3355|
|Renal tumor invading the inferior vena cava - almost, but not exclusively malignant|
Tumoral invasion of IVC is a life-threatening condition. Most often a feature of malignant pathology has to be confirmed and characterised by imaging. In rare circumstances benign tumors can also extend into IVC, behavior which mimics malignancy. On rare occasions renal AMLs may show extension into renal vein and IVC. The intravascular extension of this fatty lesion indicates an aggressive element.
Renal AML is a benign tumor of the kidneys. Typically it is a solid tumor composed of varying amounts of 3 elements: mature adipose tissue, smooth muscle cell components and abnormal thick-walled blood vessels. Renal AMLs can be both sporadically (80%) and as a part of a genetic syndrome ex. TS (tuberous sclerosis) or lymphangioleiomyomatosis (20%) [1-3].
-aprox. 1% of surgically removed renal tumors;
-without TS: mean age= 45-55 years, female predominance (F:M=4:1) .
-belongs to the family of PEComa (perivascular epithelioid cell tumors) .
2 types: -classic AML: abundant in fat cells;
-fat poor subtypes: contains too little fat to be detected on unenhanced CT .
-rare mesenchimal neoplasm, composed of numerous atypical epithelioid muscle cells, with few or no fat cells;
-histologically, these tumors can resemble and be misdiagnosed as sarcomatoid or high grade RCC;
-potentially malignant, locally aggressive and metastasize .
-positive for melanocytic markers (HMB45, HMB50, CD63, tyrosinase, Mart1/Melan A and microophthalmia transcription factor) and smooth muscle markers (smooth muscle actin, muscle-specific actin and calponin);
-epithelial markers are always negative;
-may also be positive : CD68, neuron-specific enolase, S-100 protein, estrogen and progesterone receptors, and desmin .
-cortex or medulla of the kidney;
-multifocal or bilateral AMLs highly suggestive for TS;
-extrarenal, retroperitoneal growth- can occur;
-rarely AML shows an aggressive behavior extending into the renal vein and IVC; vascular invasion has been sometimes misinterpreted as malignant .
In patients without TS:
-urinary tract infections;
-spontaneous retroperitoneal hemorrhage (size of the lesion >4cm) [2,3].
Angiomiolypoma diagnosis is sugested by the presence of intratumoral fat, but the imaging appearance sometimes varies because of its variable composition . Next the radiological appearance of classic, abundant in fat cells AML is presented:
-well-circumscribed mass, hyperechoic to renal parenchyma, often as hyperechoic as renal sinus fat, with variable posterior acoustic shadowing, showing no Doppler signal (Fig. 1) ;
-on CEUS (contrast-enhanced US) AMLs enhance nonspecifically, less than the normal renal cortex, often with a predominantly peripheral enhancement pattern ;
-US can not be used alone to diagnose AML because RCC (renal cell carcinoma) may also be hyperechoic and hypovascular .
-the value of CT consists in identifying the fat content;
-well-defined, heterogenous mass, containing macroscopic fat (with attentuation values lower than -10UH) (Fig. 2);
-no calcifications (can coexist, but only after hemorrhage); presence of calcifications inside a fat-containing renal tumor is more frequently a feature of renal carcinoma;
-hemorrhage may mask intratumoral fat .
-high signal on T1 and T2 weighted images with loss of signal intensity on fat-suppressed sequences (Fig. 3A,B);
-India ink artifact at the interface between fat and non-fat components (AML/kidney interface) on opposed-phase chemical shift MRI (Fig. 3C) .
-clusters of saccular microaneurisms or macroaneurysms;
-absent arteriovenous shunting;
-arterial phase: hipervascular, sharply marginated mass, dense early arterial network, tortuous vessels- “sunburst” appearance Fig. 4;
-venous phase: whorled “onion peel” appearance of peripheral vessels .
-retroperitoneal hemorrhage in lesions >4cm; Wunderlich syndrome is described as shock due to severe hemorrhage from ruptured AML (Fig.5);
-pulmonary embolism due to fragmentation of the thrombus or extension into pulmonary arteries via renal vein, IVC and right heart (Fig. 6).
-small, found incidentally: no treatment, although follow-up is recommended for growth assessment (not for solitary AMLs <20mm); if they are growing radiofrequency ablation or cryoablation may be effective;
-large (>4cm) or symptomatic tumors: surgical treatment (partial/ total nephrectomy);
-aggressive AML (renal vein, IVC tumor thrombus): removed surgically, even if it is asymptomatic (nephron sparing or radical nephrectomy) + caval thrombectomy; implanting temporary IVC filter in the suprarenal position can decrease the risk of pulmonary embolism and avoid potential side effects of permanent filter (Fig.7) ;
-AMLs with spontaneous, life-threatening hemorrhage: emergency selective transarterial embolization ;
-patients with life-threatening pulmonary embolism: urgent surgery .
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ECR 2019 / C-3724
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