Pictorial Essay. CT Appearances of Intraabdominal and Intrapelvic Fatty Lesions

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1 C T allows determination of the density of all tissues with fat measurements ranging from 40 to 100 H. Often, recognition of low density within a lesion allows a definitive diagnosis to be made. The purpose of this pictorial essay is to review intraabdominal fatty lesions with an emphasis on the role of CT in their detection and diagnosis. CT ppearances of Intraabdominal and Intrapelvic Fatty Lesions Luis Méndez-Uriburu 1, Jorge hualli, Julio Méndez-Uriburu, Martín Méndez-Uriburu, Luis Fajre, Federico Méndez-Uriburu, Ramón Carabajal Liver Fatty hepatic neoplasms include angiomyolipoma, lipoma, myelolipoma, liposarcoma, and metastases from other primarily fatty tumors [1]. ngiomyolipomas consist of fat and blood vessels and present as well-defined masses, with attenuation values associated with fat and more dense areas of angiomuscular tissue that may enhance with IV administration of contrast material (Figs. 1 and 2). Lipomas are encapsulated tumors composed of adipose tissue that present as well-defined round masses with a visible and homogeneous wall and, unlike angiomyolipomas, show an absence of enhancement after contrast administration [1]. Liver liposarcomas are extremely rare tumors [1]. To our knowledge, only a few cases of liver liposarcoma have been reported in the literature. Imaging of a documented case showed a cm mass in the hilum of the liver that extended to the retroperitoneum. The mass had well-defined borders and an inhomogeneous structure. Fatty areas had attenuation values of less than 20 H on CT scans. Other components of the mass had attenuation values in the intermediate range. No evidence of surrounding soft-tissue edema or contrast enhancement was present [2]. Rarely, metastases to the liver can contain fat. One possible primary site would be a teratoma (metastatic teratomatous hepatic implantations) [1]. Pictorial Essay Pancreas The major histologic finding of pancreatic lipomatosis is the presence of fatty deposits in the parenchyma. Pancreatic lipomatosis may occur in obese and diabetic patients with varying levels of pancreatic insufficiency. It may also manifest in patients with cystic fibrosis or diseases such as Shwachman syndrome and Johanson-lizzard syndrome. In advanced stages of pancreatic lipomatosis, the whole parenchyma is replaced by fat, and the pancreatic duct is identified as a linear density [3] (Fig. 3). Focal fatty infiltration of the pancreas refers to a focal region of pancreatic parenchyma that on CT shows normal or lower density compared with that of the surrounding pancreas. In focal pancreatic infiltration, contrast-enhanced CT reveals low-attenuation tissue interposed between normal pancreatic parenchyma that can mimic a hypoattenuating mass (cystic or solid neoplasm) [4] (Fig. 4). Fig year-old woman with echogenic nodule that was detected on sonography and suspected of being hemangioma. CT scan reveals well-defined oval mass (arrow) with attenuation values of fatty tissue ( 57 H) and consistent with angiomyolipoma, which was confirmed by percutaneous fine-needle biopsy. Received November 6, 2003; accepted after revision pril 15, ll authors: Centro Radiológico Luis Méndez Collado, Muñecas 444, San Miguel de Tucumán, Tucumán 4000, República rgentina. ddress correspondence to L. Méndez-Uriburu (luismu@mendezcollado.com). JR 2004;183: X/04/ merican Roentgen Ray Society 933

2 Méndez-Uriburu et al. Fig year-old woman who presented with nonspecific abdominal pain., Contrast-enhanced CT scan incidentally reveals intrahepatic focal fatty lesion ( 27 H) containing thin septa that was interpreted as hepatic angiomyolipoma., Contrast-enhanced CT scan obtained 2 years later shows no changes from previous scan (). Fine-needle biopsy confirmed diagnosis of hepatic angiomyolipoma. Fig year-old obese man with diabetes and pancreatic lipomatosis. bdominal CT scan reveals pancreatic parenchyma has been completely replaced by fatty tissue with marked glandular atrophy. Note dense acini (arrows) separated by increased fatty tissue. Fig year-old man with focal fatty infiltration of pancreas. Helical CT scan shows hypoattenuating pancreatic mass (arrow) that does not deform border and has typical fatty density ( 40 H), indicating mass is composed of fat. 934

3 Fig year-old man with anemia. CT scan shows well-defined intragastric mass inlesions pyct of Fatty loric segment. Mass has smooth margins (arrows) and attenuation of 99 H, consistent with gastric lipoma. Fig year-old woman with bladder cancer. Contrast-enhanced CT scan reveals polypoid lesion extending through proximal duodenum (arrow), with typical fatty density ( 43 H). Lesion is surrounded by air (arrowheads) and duodenal walls. Endoscopy confirmed transpyloric prolapse of gastric lipoma. Fig year-old man who presented with dyspepsia and vomiting., CT scan was obtained using oral but no IV contrast agent with patient in dorsal decubitus position. Fat-density mass (arrow) surrounded by air (arrowheads) and intestinal fluid is revealed and cystic mass (asterisk) is visible on outer margin of right kidney., CT scan was obtained with patient in right lateral decubitus position after second administration of oral contrast agent and first administration of IV contrast agent. Intraduodenal fatty lesion (arrow), surrounded by second dose of oral contrast agent, can be clearly seen. 935

4 Méndez-Uriburu et al. Fig year-old man with history of testicular tumor. CT scan shows incidentally found oval fatty lesion (arrow) in third section of duodenum in front of aorta and inferior vena cava. Lesion is of homogeneous fat density, consistent with duodenal lipoma. Gastrointestinal Tract Gastrointestinal lipomas are circumscribed tumors with a uniform fat attenuation depicted on CT scans [1]. The typical presentation is as polypoid masses that are generally found in the submucosa of the gastrointestinal tract, most frequently in the large and small intestines [1]. Given their appearance and features, gastrointestinal lipomas can be definitively diagnosed on CT in most cases [5] (Figs. 5 10). Liposarcomas are common soft-tissue neoplasms but are rarely present in the gastrointesti- nal tract. They have a more inhomogeneous appearance than their benign counterparts, lipomas, because of the presence of more solid and myxoid elements besides fat. This mixed composition explains the variable appearance of these tumors on CT [5, 6]. Fig year-old woman with abdominal colic., Oral contrast-enhanced CT scan reveals round intraluminal mass (arrow), characterized by fat-attenuation mass (tip of lipoma) and thin halo (arrowheads), which is suggestive of mesenteric fat resulting from intestinal intussusception., CT scan (2 cm caudal to ) shows lipoma (arrow) clearly as lead point in small-bowel intussusception. C, CT scan obtained with patient in right lateral decubitus position shows lesion (arrow) involves different layers of small intestine and highlights its homogeneous fat density. C 936

5 CT of Fatty Lesions Fig year-old woman with colonic lipoma. CT scan obtained with oral and IV contrast material shows colonic mass (arrow) on proximal part of transverse colon with density and characteristics identical to those of adipose tissue. Mesentery Mesenteric panniculitis is a rare condition characterized by a nonspecific chronic disorder in the adipose tissue of the intestinal mesentery [7]. The most characteristic CT findings include superior mesenteric veins surrounded by a well-defined fatty mass, movement of intestinal loops, well-differentiated nodules in the soft tissue smaller than 5 mm in diameter [7], and mass effect on the adjacent organs. (Fig. 11) In such cases, the term misty mesentery is often applied. This term refers to increased attenuation in the mesentery, but this sign is not specific for mesenteric panniculitis. ny process that infiltrates the mesentery can result in a misty mesentery. Therefore, hemorrhage, edema, or tumor (lymphoma) can have an appearance similar to that of mesenteric panniculitis [8] (Fig. 12). Cavitating mesenteric lymph node syndrome is an uncommon and poorly understood complication of celiac disease. Multiple cystic masses containing thin and milky or thick and creamy material are present along the jejunoileal mesentery. In Fig year-old man with history of treated lymphoma and misty mesentery. CT scan shows heterogeneous increase in fat surrounding mesentery root (arrows) results in thin peripheral capsule and mass effect on loops of adjacent small intestine (arrowheads). Fig year-old man with mesenteric panniculitis. Unenhanced abdominal CT scan shows discrete increase (arrowheads) in density of fatty tissue surrounding mesenteric vessels without displacement. Note thin halo of normal fatty tissue surrounding mesenteric vessels. some cases, very low attenuation is noted within these multiple cystic masses, indicating fat [9] (Fig. 13). Lipomatous neoplasms and lymphangiomas of the mesentery are quite uncommon. drenal Gland drenal myelolipomas are relatively rare tumors composed of mature fatty tissue associated with proliferating hematopoietic cells. t biopsy, the reported prevalence of this tumor has ranged from 0.08% to 0.4% [9]. The most Fig year-old woman with cavitating mesenteric lymph node syndrome. Helical CT scan obtained after administration of oral and IV contrast material shows multiple rounded fluid-attenuation (10 H) masses with thin walls (arrows) in mesentery. Some masses have lower attenuation values ( 50 H) (arrowheads) indicating fatty material. 937

6 Méndez-Uriburu et al. Fig year-old woman with adrenal myelolipoma. Helical CT scan obtained without IV contrast agent shows right adrenal mass (long arrow) with heterogeneous density in more dense central area (short arrow) and fatty density in peripheral area ( 102 H). Fig year-old man who presented with adrenal myelolipoma., CT scan shows well-defined adrenal mass (arrow) characterized by low-attenuation tissue ( 84 H) reflecting fat in myelolipoma, mixed with bone marrow elements., CT scan obtained 7 years after shows persistent right adrenal lesion (arrow) with same appearance and size as in previous scan () but with slight increase in its density, probably because of higher content of hematopoietic tissue within it. Fig year-old woman with occult blood in feces. Enhanced CT scan shows tumor (4cm diameter) (arrow) on outer margin of right kidney with fatty density pattern ( 81 H) and more dense lineal areas characteristic of renal angiomyolipoma. 938

7 CT of Fatty Lesions Fig year-old woman with renal mass depicted on sonography. CT scan obtained with oral and IV contrast material shows typical fatty mass containing vessels and tissues located in front of left kidney (white arrow), with defect present in renal parenchyma (black arrow) that shows renal origin of lesion, thus differentiating renal angiomyolipoma from retroperitoneal liposarcoma. Fig year-old woman with tuberous sclerosis and large bilateral renal angiomyolipomas. CT scan shows several lesions with fatty content (long arrows) generously projecting to perinephric space. Thus, serpentine vascular structures (short arrows) located within lesions can be clearly seen. Fig year-old woman with hemorrhagic renal angiomyolipoma., Helical CT scan obtained without contrast agent shows large heterogeneous tumor mass (white arrow) measuring about 8 cm, with fatty content and more dense areas suggestive of intratumoral hemorrhage (black arrow). Note discrete hyperdensity compared with adjacent muscular structures., Contrast-enhanced helical CT scan shows that fatty lesion (white arrow) is associated with renal parenchyma, which is laterally displaced by lesion. Hemorrhage resulting from rupture of intratumoral aneurysm is more clearly seen in sloping region (black arrow). 939

8 Méndez-Uriburu et al. Fig year-old woman with malignant melanoma. Contrast-enhanced CT scan of abdomen reveals lipoma (arrow) in left kidney resembling simple renal cyst but with completely homogeneous fatty density ( 99 H). (Compare with density of intestinal air and subcutaneous fat.) Note absence of vessels and tissue within lesion, findings that differ from those of angiomyolipomas. Fig year-old man with left renal sinus lipomatosis. CT scan shows highly increased fatty deposit in left renal sinus (arrow) that surrounds and compresses collecting system. Renal parenchyma thickness (arrowheads) is slightly reduced, and thin calcifications are seen in gallbladder. Fig. 22. Replacement lipomatosis in 50-year-old woman with uterine cervix adenocarcinoma. CT scan obtained without IV contrast agent shows changes in right renal parenchyma associated with generous fatty infiltration (arrow) of both renal parenchyma and perinephric space. Renal pelvis shows calcific staghorn lithiasis (asterisk). 940

9 CT of Fatty Lesions Fig year-old woman with palpable mass in pelvis., CT scan obtained with patient in supine decubitus position reveals large tumor mass with two well-defined areas with different densities. Higher area (asterisk) has density of 90 H (slightly lower than adjacent fat), whereas sloping portion (arrow) has intermediate density ranging between that of fat and that of soft tissues. Compare density with that of psoas major. Presence of floating hairy mass is seen as wave on horizontal level., On CT scan obtained with patient in prone decubitus position, septa can be seen inside mass (arrow), with mobility of the fluid fatty content due to presence of fatty tissues of different weights. Fig year-old woman referred for suspected dermoid cyst. CT scan shows typical appearance of mature cystic teratoma (dermoid cyst), with components of three germinative layers consisting of low-density fatty tissue (straight arrow), teeth (curved arrow), and structures with attenuation similar to that of abdominal musculature (arrowheads). Fig year-old woman with ovarian lipoma. Helical CT scan shows well-defined tumor in right adnexal region with smooth margins (arrow) and attenuation of 47 H. Surgery confirmed diagnosis. 941

10 Méndez-Uriburu et al. Fig year-old man with hematuria. CT scan shows well-defined, homogeneous mass (arrow) with generous fatty content ( 107 H) and discrete mass effect on loops of adjacent small intestine, which are characteristic of retroperitoneal lipoma. bsence of more dense areas within lesion allows differentiation from liposarcoma. relevant CT findings are of fatty tissue. The attenuation levels are higher than those seen in the retroperitoneal fat on CT scans because of the presence of hematopoietic tissue in the myelolipoma [10] (Figs. 14 and 15). Kidney Renal angiomyolipomas are renal masses composed of abnormal blood vessels, mature fat, and smooth muscle that may be associated with hemorrhage, necrosis, and dystrophic calcification [11]. CT findings of this tumor reveal the presence of a well-defined heterogeneous renal mass reflecting the amount of fatty, muscular, and vascular tissue within it. The administration of a contrast agent contributes to enhancement of solid areas, which is directly related to the existing vascular structures [11] (Figs ). leeding may disguise the areas of fatty density, consequently presenting difficulties to making the diagnosis. We present a case that posed no such difficulty [11] (Fig. 19). Renal lipomas are unusual benign tumors of the kidney exclusively composed of adipose tissue [11] (Fig. 20). On CT, simple lipomas display fat attenuation and do not enhance after contrast material administration. Renal sinus lipomatosis is an excessive accumulation of fat in the renal sinus that may occur in obese or normal-weight patients. On excretory urography, this fatty tissue may resemble a peripyelic mass, with compression of calyx structures. On CT, the origin of this condition can be determined according to its characteristic density [11] (Fig. 21). Replacement lipomatosis of the kidney is an advanced type of renal sinus lipomatosis. This condition occurs with parenchymal atrophy associated with a proliferation of the renal sinus fat [1, 12] (Fig. 22). The presence of both a staghorn calculus and the atrophic renal parenchyma is easily depicted on CT. The characteristic distribution of fat within the renal sinus and the perinephric space is suggestive of this process. Replacement lipomatosis of the kidney should be differentiated from xanthogranulomatous pyelonephritis [12]. The latter may display hydronephrosis and pyonephrosis surrounded by xanthogranulomatous tissue with a watery density [13]. Other entities less frequently found in the kidney but containing fat density are renal capsule liposarcomas, [1] Wilms tumors, and renal cell carcinomas [11, 14]. Ovary Ovarian teratomas are the most frequent germ cell neoplasms. They are tumors composed of different histologic types (mature cystic teratoma, immature teratoma, and monodermal teratoma), containing mature or immature tissue produced in the germ cells [15]. On CT, fat attenuation within a cyst, with or without wall calcification, is indicative of mature cystic teratoma, which is the most common ovarian teratoma [15] (Fig. 23). On occasion, a floating hairy mass is found in a fat water interface. The presence of fat is reported in 93% of the cases, whereas teeth and other calcifications are found in 56% [15] (Fig. 24). Nonteratomatous lipomatous ovarian tumors (ovarian lipoleiomyoma and ovarian lipoma) are extremely rare tumors. n ovarian lipoleiomyoma is a predominantly solid leiomyomatous mass of intermediate density with a scattering of multiple focal (1 3 cm) fat-density nodules. The differential diagnosis of a pure lipomatous mass of obvious ovarian origin includes benign cystic ovarian teratoma and ovarian lipoma [16] (Fig. 25). Fig year-old woman with retroperitoneal liposarcoma. CT scan obtained with oral and IV contrast materials shows huge retroperitoneal tumor mass (long arrows) with heterogeneous fatty density that has septa (short arrows) and well-defined lobulated contours. Mass effect on adjacent structures is evident, but no infiltration is seen. Left kidney is in contact with but is not infiltrated by tumor. Uterus Lipomatous uterine tumors are rare benign neoplasms. The histologic spectrum includes 942

11 CT of Fatty Lesions pure lipomas, lipoleiomyomas, and fibromyolipomas. Histologically, they are composed of smooth muscle, fat cells, and fibrous tissue in various ratios. lthough pure lipomas have been reported, most of these tumors contain various compositions of mesodermal tissues. lipomatous pelvic mass of obvious uterine origin may be diagnostic for this entity. The masses may be endophytic or exophytic to the uterus. When a mass is exophytic, the diagnosis is more difficult because its appearance mimics those of ovarian fatty tumors that are more common [16, 17]. Retroperitoneum Retroperitoneal liposarcoma is the most frequently retroperitoneal neoplasia found in adult patients, with a variable appearance on CT [1]. It can be classified into differentiated, pleomorphic, myxoid, and poorly differentiated. Differentiated liposarcomas present a generous amount of fat easily depicted on CT that, combined with heterogeneity, allows differentiating this condition from retroperitoneal lipoma. The latter is a very rare condition that, unlike liposarcoma, presents a homogeneously fatty density with scarce mass effect on the adjacent structures [18] (Figs. 26 and 27). References 1. Fultz PJ, Hampton WR, Skucas J, Sickel JZ. Differential diagnosis of fat-containing lesions with abdominal and pelvic CT. RadioGraphics 1993;13: ribal E, erberoglu U. Primary liposarcoma of the liver. JR 1993;161: Gore MD, Fernbach SK. Pancreatic insufficiency and cystic fibrosis. In: Gore RM, Levine MS, Laufer I, eds. Textbook of gastrointestinal radiology, 1st ed. Philadelphia, P: Saunders, 1994: Isserow J, Siegelman ES, Mammone J. Focal fatty infiltration of the pancreas: MR characterization with chemical shift imaging. JR 1999;173: Park SH, Han JK, Kim TK, et al. Unusual gastric tumors: radiologic-pathologic correlation. Radio- Graphics 1999;19: Levy D, Remotti HE, Thompson WM, Sobin LH, Miettinen M. Gastrointestinal stromal tumors: radiologic features with pathologic correlation. RadioGraphics 2003;23: Daskalogiannaki M, Voloudaki, Prassopoulos P, et al. CT evaluation of mesenteric panniculitis: prevalence and associated diseases. JR 2000;174: Horton KM, Lawler LP, Fishman EK. CT findings in sclerosing mesenteritis (panniculitis): spectrum of disease. RadioGraphics 2003;23: Huppert J, Farrell M. Case 60: cavitating mesenteric lymph node syndrome. Radiology 2003;228: Otal P, Escourrou G, Mazerolles C, et al. Imaging features of uncommon adrenal masses with histopathologic correlation. RadioGraphics 1999;19: Hélénon O, Merran S, Paraf F, et al. Unusual fatcontaining tumors of the kidney: a diagnostic dilemma. RadioGraphics 1997;17: Karasick S, Wechsler RJ. Case 23: replacement lipomatosis of the kidney. Radiology 2000;215: De Velásquez R, Yader I, Velásquez P, Papanicolau N. Imaging the effects of diabetes on the genitourinary system. RadioGraphics 1995;15: Helenon O, Chretien Y, Paraf F, et al. Renal cell carcinoma containing fat: demonstration with CT. Radiology 1993;188: Outwater EK, Siegelman ES, Hunt JL. Ovarian teratomas: tumor types and imaging characteristics. RadioGraphics 2001;21: Dodd GD III, udzik RF Jr. Lipomatous tumors of the pelvis in women: spectrum of imaging findings. JR 1990;155: Ishigami K, Yoshimitsu K, Honda H, et al. Uterine lipoleiomyoma: MRI appearances. bdom Imaging 1998;23: Nishino M, Hayakawa K, Minami M, Yamamoto, Ueda H, Takasu K. Primary retroperitoneal neoplasms: CT and MR imaging findings with anatomic and pathologic diagnostic clues. Radio- Graphics 2003;23: