1 Condi&ons Associated with Macroscopic Fat in the Genitourinary System: A Review From Top to Bo>om Katryana Hanley- Knutson, MD, Christopher Brady, MD and Ray Dyer, MD Department of Radiology, Wake Forest School of Medicine Winston- Salem, NC
2 Processes producing macroscopic fat in the Genitourinary (GU) system include benign and malignant condi&ons, as well as responses to therapy. Fat may appear in or adjacent to any structure along the length of the GU system. This exhibit illustrates a number of these processes.
3 DX: Adrenal adenoma with fa0y degenera3on. Small focus of macroscopic fat (arrow) in a les adrenal mass. At resec&on, this was shown to be an adenoma with lipomatous metaplasia. Macroscopic fat in an adrenal nodule is more typical of myelolipoma and is rarely seen with adrenal cor&cal carcinoma. MRI with in- and out- of- phase imaging may demonstrate intracellular lipid throughout the mass which is diagnos&c of adenoma. The majority of myelolipomas are predominantly composed of macroscopic fat.
4 DX: Adrenal myelolipoma. A large les adrenal mass contains macroscopic fat (arrow) and sos &ssue (hematopoie&c) elements (*). Imaging features are diagnos&c of myelolipoma. * Usually asymptoma&c. Large lesions may produce symptoms from mass effect and may undergo spontaneous rupture and hemorrhage. Lesions larger than 7 cm should be considered for surgical resec&on.
5 DX: Spontaneous hemorrhage of a le9 myelolipoma. CT image shows hemorrhage (arrow) into an adrenal mass that had been previously characterized as a myelolipoma. The hemorrhage obscures the fa>y elements of the adrenal mass.
6 DX: Extraadrenal, perirenal myelolipomas (arrows). This is an unusual case of mul&ple masses surrounding both kidneys that contain macroscopic fat and sos &ssue elements. Masses are confined by Gerota s fascia and there is no renal parenchymal defect to suggest a renal origin (such as an angiomyolipoma, or AML). Appearance suggests a benign e&ology. Stability on follow- up or biopsy may be necessary to establish the diagnosis and exclude retroperitoneal liposarcoma.
7 DX: Myelolipoma and extraadrenal myelolipoma. A large right adrenal mass (arrow) containing macroscopic fat is consistent with a myelolipoma. The les para- aor&c mass (arrowhead) has a similar appearance, and also contains macroscopic fat. This was resected and shown to be an extraadrenal myelolipoma. Extraadrenal myelolipomas are rare and most commonly occur in the presacral space, but may occur in the medias&num, abdomen and muscle fascia. Resec&on may be indicated to exclude retroperitoneal liposarcoma.
8 Kidney sag Fig. 1 Fig. 2 Fig. 3 DX: Angiomyolipoma (AML). Circumscribed, echogenic renal mass (arrow, Fig. 1). Echogenicity is similar to that of the renal sinus fat. Based on the US, this lesion is most likely an AML; however, renal cell carcinoma (RCC) may also be hyperechoic (more common with small RCCs). CT in the same pa&ent (Fig. 2) confirms the presence of macroscopic fat (arrow) in the renal mass, consistent with an AML. Macroscopic fat within an RCC is extremely rare (look for other features to suggest malignancy). Follow- up imaging can be used to assess stability of small lesions. Larger lesions (typically >4 cm) are at greater risk of hemorrhage. Prophylac&c par&al nephrectomy or emboliza&on may be considered in such cases. A CT image from a different pa&ent (Fig. 3) who presented with acute flank pain shows spontaneous hemorrhage surrounding an AML (arrow).
9 DX: Fat within a parenchymal scar. Fig. 1 Fig. 1 is another case, where based on the ultrasound appearance, the main differen&al diagnos&c considera&ons include AML and RCC (arrow). CT in the same pa&ent, however (Fig. 2), confirms a parenchymal scar with no evidence of a mass (arrow). Fig. 2 The findings on ultrasound are nonspecific and should prompt further evalua&on with CT or MRI.
10 Fig. 1 Fig. 2 Kidney sag DX: Mul3ple, bilateral AMLs in tuberous sclerosis (TS). Ultrasound demonstrates mul&ple hyperechoic masses throughout the right kidney (Fig. 1). The les kidney (not shown) had a similar appearance. CT confirms mul&ple fat containing masses within both kidneys, consistent with AMLs (Fig. 2). 70%- 95% of pa&ents with TS will have mul&ple, bilateral renal AMLs. AMLs associated with TS tend to present earlier, grow faster and have a higher incidence of hemorrhage.
11 DX: Replacement lipomatosis. Fig. 1 Fig. 2 CT demonstrates severe parenchymal atrophy, hydronephrosis (or pyonephrosis), renal calculi, and fa>y prolifera&on in the renal sinus, perinephric space and retroperitoneum, the hallmarks of replacement lipomatosis (Fig. 1-3). The main differen&al diagnosis is xanthogranulomatous pyelonephri&s (XGP). In replacement lipomatosis, fat cells do not infiltrate the renal parenchyma, whereas infiltra&on of the parenchyma by lipid- laden macrophages is seen with XGP. Liposarcoma might also be included in the differen&al diagnosis, depending on the history and imaging findings. Surgery may be necessary to alleviate symptoms and establish a defini&ve diagnosis. Fig. 3
12 DX: Cyst decor3ca3on with fat- fluid level. The presence of a fat- fluid level (arrow) in a renal lesion is unusual; however it may rarely be seen in a cys&c lesion. This should prompt correla&on with surgical history. CT in les side down posi&on This should not be confused with a focus of fat in a solid renal mass, such as AML.
13 Fig. 1 DX: Retroperitoneal lipomatosis. Fig. 2 Expansion of the retroperitoneal compartments with fat (arrowheads, Fig. 1, 2), right greater than les, with displacement of retroperitoneal and abdominal structures towards the anterior midline (arrows).
14 DX: Retroperitoneal teratoma. Retroperitoneal mass (arrow) contains macroscopic fat, sos &ssue density elements and calcifica&on. Differen&al diagnosis includes retroperitoneal liposarcoma, extraadrenal myelolipoma and retroperitoneal teratoma. In a male pa&ent, consider metasta&c disease from a tes&cular primary. Fat and calcifica&on present in up to 83% and 93% of lesions, respec&vely. Usually benign, but necrosis and hemorrhage would suggest malignancy. Surgical resec&on is indicated.
15 DX: Teratoma. Pelvic mass (arrow) contains fat, calcifica&on (in this case a tooth), and sos &ssue a>enua&on material. Findings are virtually pathognomonic. Most teratomas are benign and they are the most common ovarian neoplasm in women under 45 years of age. Symptoms may result from mass effect, local invasion, or ovarian torsion. Surgical resec&on is treatment of choice. Chemotherapy and radia&on therapy reserved for select cases.
16 DX: Teratoma (i.e., dermoid). Ultrasound image of the les adnexa in a different pa&ent shows a typical appearance of an ovarian teratoma (i.e., dermoid). The echogenic nodule within the mass is the Rokitansky nodule, or dermoid plug (arrow). Shadowing may be due to fat or calcifica&on in the dermoid plug. The dot- dash appearance of the cys&c component is secondary to hair mixed within the cyst fluid (typically sebum). Poten&al mimics include hemorrhagic cyst, bowel, perforated appendici&s or fibrous lesions such as cystadenofibromas.
17 DX: Uterine lipoleiomyoma. Uterus- sag There is a circumscribed, hyperechoic mass in the uterus (arrow), surrounded by normal myometrium. Lipoleiomyomas are rare, benign neoplasms of the uterus. Typically found in postmenopausal women. Similar to other leiomyomas in their clinical course. Must be differen&ated from an ovarian mass (teratoma), as teratomas require surgical excision and asymptoma&c lipoleiomyomas require no treatment.
18 Fig. 1 DX: Uterine lipoleiomyoma. If there is any ques&on about the origin or e&ology of a pelvic mass on ultrasound, pelvic MRI may be helpful for further characteriza&on. Fig. 2 In this case, there is a mass in the uterus with similar signal intensity to fat on T1 weighted imaging (arrow, Fig. 1), which becomes hypointense on fat- saturated T2 weighted imaging (arrow, Fig. 2), consistent with lipoleiomyoma.
19 DX: Uterine lipoleiomyoma. Fig. 1 Axial (Fig. 1) and sagi>al (Fig. 2) CT images show a large mass arising from the uterine fundus that contains macroscopic fat intermixed with areas of sos &ssue density, consistent with a lipoleiomyoma. Fig. 2
20 TRANS LT TESTICLE MID DX: Tes3cular lipomas versus hamartomas. Fig. 1. Figs. 1 & 2 demonstrate mul&ple sca>ered echogenic lesions (yellow arrows) in the bilateral tes&cles of a 43 year- old- man, consistent with tes&cular lipomas and/or hamartomas. The largest measured 4 mm. No lesion demonstrated increased vascularity. TRANS RT TESTICLE MID Mul&ple tes&cular lipomas and/or hamartomas can be seen in Cowden syndrome. These pa&ents have an increased risk of visceral and cutaneous neoplasms. Fig. 2. Biopsy of the tes&cular lipomas/ hamartomas is NOT recommended.
21 DX: Pelvic lipomatosis. Fig. 1 This condi&on is characterized by deposi&on of unencapsulated fat in the anatomic pelvis (fat arrows, Figs. 1-3,) unrelated to obesity, and may develop in response to inflammatory insults. Note the bladder is compressed (thin arrows) and there is medializa&on of the inferior ureters (arrowhead, Fig. 3) as a result of mass effect from the fat. There is a ureteral stone, too, on the les (curved arrow, Fig. 1). This condi&on is more common in men, and in the African- American popula&on and may be associated with cys&&s glandularis. Plain film may demonstrate a perivesicle lucency. Fig. 2 Fig. 3
22 Fig. 1 Fig. 2 Fig. 3 DX: Retroperitoneal liposarcoma. CT images (Figs. 1, 2) show a large fat containing mass in the retroperitoneum extending through the inguinal canal into the scrotum. SoS &ssue elements and calciﬁca&ons are also seen in the mass (arrow). Ultrasound image in the same pa&ent shows extension of the process into the inguinal canal, with similar echogenicity to abdominal fat (arrow, Fig. 3). Based on ultrasound, the main diagnos&c considera&ons are extrates&cular neoplasm or inguinal hernia, which led to performance of the CT exam.
23 DX: Papillary RCC with foci of cholesterol necrosis. Fig. 1 Fig. 2 Unenhanced (Fig. 1) and enhanced (Fig. 2) CT images show a large, heterogeneous right renal mass with cys&c and solid components. There are focal areas of calcifica&on and several &ny globules of fat within the mass (arrows). Macroscopic fat within an RCC is rare (more commonly seen with large masses), however this should not be confused for an AML.
24 Fig. 1 Fig. 2 DX: Teratomatosis. Images through the lower abdomen and upper anatomic pelvis show mul&ple heterogeneous masses that contain collec&ons of macroscopic fat (arrows, Figs. 1, 2). This finding was the result of rupture of high grade, immature teratoma with dissemina&on of the contents.
25 Fig. 1. DX: Renal halo sign aser radiofrequency abla&on (RFA) of RCC. A biopsy proven RCC is seen on pre- procedure imaging (arrow, Fig. 1). Pa&ent then underwent RFA. Fig. 2 On follow- up imaging (arrow, Fig. 2), the renal halo sign (macroscopic fat surrounding the treated tumor with thin rim of sos &ssue) is present. This should be recognized as an expected post- RFA appearance (present aser 75% of RFAs) and not confused for residual tumor or AML. Similar findings may be seen aser cryoabla&on.
26 Fig. 1. DX: Fat used to fill a surgical defect. Fig. 1 is a preopera&ve CT exam showing an enhancing mass in the upper pole of the right kidney (arrow) that was proven to be an RCC. Fig. 2. A follow- up CT (Fig. 2) aser par&al nephrectomy with fat packing of the surgical defect shows the typical post- opera&ve appearance (arrow). Without the appropriate history, this might be confused for an AML and ini&ate follow- up imaging or interven&on.
27 Fig. 1 DX: Chyluria aser RFA. Fat- fluid level in the urinary bladder (arrow, Fig. 1) in this pa&ent who had previously undergone renal RFA (Fig. 2). Fig. 2 Chyluria may result from lympha&c injury aser RFA, par&al nephrectomy, or trauma. This should not be confused for intramural fat or air in the bladder (assess HUs and view in lung windows) which would change the differen&al diagnosis. Typically requires no treatment.
28 Macroscopic fat, iden&fiable at imaging, may be seen in benign and malignant condi&ons of the GU system and aser treatment of some of these condi&ons. Recogni&on of the fat content, when coupled with the clinical presenta&on, will assist in making a correct diagnosis (and poten&ally avoiding a misdiagnosis) and direc&ng therapy.
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