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307

Case Report :

,

Intratumoral Fat in a Renal Angiomyolipoma Nancy

S. Curry,1

Stephen

I. Schabel,1

A. Julian

Oncocytoma

Garvin,2

A recent publication and other sources in the nadiologic literature state that when CT shows definitive fat within a renal mass, renal cell carcinoma can be excluded and angiomyolipoma can be established as the diagnosis [i -4]. We report a renal mass that was proved to be an oncocytoma containing focal areas of intnatumonal, engulfed sinus fat. This finding should not be misinterpreted as intrinsic tumor fat, which would lead to the erroneous diagnosis of angiomyolipoma.

and George

Mimicking

Fish3

were several isolated clusters of mature adipocytes completely sunrounded by tumor cells (Fig. 1D). The right kidney contained multiple tumor nodules with the same microscopic appearance as those in the left kidney except that intratumoral fat deposits were not noted. Ultrastructural examination of these tumors showed abundant cytoplasmic

mitochondnia

in the tumor

cells,

characteristic

mas. The mature adipose tissue was thought trapped within the expansile tumor mass.

of oncocyto-

to be renal sinus fat

Discussion Case

Report

,

A 64-year-old woman presented examination, renal function studies,

with abdominal pain. Physical and urinalysis were normal ex-

cept for mild pyuria. Anemia (hemoglobin

levels, 8.9 gm/dI; hemato-

crit, 27%)

rate were

and an elevated

sedimentation

present.

A renal

sonogram revealed bilateral renal masses. CT showed small, discrete areas offat density (-80 H) scattered within a large, inhomogeneous left renal mass and also within the largest of multiple right renal masses (Figs. 1A and 1B). No central scar formation was apparent. The tumors were moderately hypervascular on angiography but did not show

“spoke-wheel”

configuration

of vessels.

Metastatic

workup

was normal. Open biopsies of both kidneys performed with the patient anesthetized were interpreted as consistent with carcinoma, and bilateral nephrectomies were performed. The patient is on chronic hemodialysis and free of metastases 1 year after surgery. Pathologic examination revealed a 15-cm, multilobulated left renal mass with areas of necrosis and hemorrhage (Fig. 1 C). The tumor did not extend through the renal capsule. Within the tumor, there

Received 1 2 3

August

Bosniak et al. [1 4] pointed out that detecting fat, even in small amounts, in a renal tumor on CT examination appnopri-

8, 1 989; accepted

after revision

October

ately identifies the lesion as a benign angiomyolipoma. The only other fatty tumors of the kidney are lipomas, liposarcomas, and teratomas, although fat elements have been found in atypical Wilms tumor [5]. Although it is accepted that renal cell carcinomas do not contain fat, Bosniak predicted that large malignant tumors could engulffat in the renal sinus on perinenal tissues, mimicking intrinsic fat. The large oncocytoma presented in this case report exhibited this characteristic, although a review of the

CT scans of 48 lange renal cell carcinomas in our teaching

files yielded

Renal oncocytoma

no other

is a benign-behaving

renal panenchyma, pathologically granular, eosinophilic cytoplasm of mitochondnia. These tumors,

5, 1989.

(>4 cm in diameter)

case of fat entrapment.

solid tumor of the

distinctive because of its packed with large numbers considered by some pathol-

Department of Radiology, Medical University of South Carolina, 171 Ashley Ave., Charieston, Sc 29425. Address reprint requests to N. S. Curry. Department of Pathology and Laboratory Medicine, Medical University of South Carolina, 171 Ashley Ave., Charleston, SC 29425. 102 Fauquier St., Fredericksburg, VA 22401.

AJR 154:307-308,

February

1990 0361-803X/90/1542-0307

C American Roentgen Ray Society

308

CURRY

ET AL.

AJA:154, February 1990

Fig.

1.-A,

CT

inhomogeneous neys. Scattered

scan

tumors

fat (-80 ent in multiple areas of B, CT scan of a more tion through renal mass

shows large, of both kidH) was presleft kidney. cephalad seein right upper

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pole shows fat along lateral

margin of

tumor. C, Cut section of tumor shows areas of hemorrhage and necrosis. 0, Photomicrograph reveals mature adipocytes within tumor.

B

ogists as low-grade carcinomas, may achieve large size but rarely metastasize [6]. Although most oncocytomas have a favorable prognosis, higher grade tumors can show locally

illustrates

that the radiologist

should

be cautious

in diagnosing

a benign renal lesion solely on the basis of detection amounts

of fat within

a large

of small

renal mass.

aggressive growth behavior, invasion of the renal pelvis and capsule, and metastasis to the lymph nodes with ultimately fatal outcome [7]. Conversely, renal cell carcinomas can exhibit oncocytic features, making the pathologic diagnosis difficult even when the entire specimen is available for study. Radiographic characteristics that have been attributed to oncocytomas include a “spoke-wheel” configuration of yes-

sels and a homogeneous capillary phase on angiognaphy and CT findings of a homogeneous mass with a central stellate scan [8]. The lack of specificity of these findings has been noted,

however,

as is illustrated

The lack of smooth

muscle

by this case.

on vascular

proliferation

along

with the intnatumonal fat makes the possibility of destruction of a preexisting angiomyolipoma unlikely. It seems even less plausible that there might have been multicentnic incidental lipomas that became surrounded by the oncocytoma. Entrapment of renal sinus fat has to be considered the most likely

reason

for the fat within

these

tumors.

This unusual

case

REFERENCES 1 . Bosniak diagnosis amounts 2. Friedman

MA, Megibow AJ, Hulnick DH, Hon 5, Aaghavendra BN. CT of renal angiomyolipoma: the importance of detecting small of fat. AJR 1988;151 :497-501 AC, Hartman DS, Sherman J, Lautin EM, Goldman M. Computed tomography of abdominal fatty masses. Radiology 1981;139:415-429

3. Hansen GC, Hoffman RB, Sample WF, Becker A. Computed tomography diagnosis of renal angiomyolipoma. Radiology 1978;128:789-791 4. Bosniak MA. Angiomyolipoma (hamartoma) diagnosis is possible in virtually every case.

of the kidney: a preoperative UrolRadiol 1981;3: 135-142

5. Parvey L5, Wamer AM, Callihan TA, Magill HL. CT demonstration of fat tissue in malignant renal neoplasms: atypical Wilms’ tumors. J Comput Assist

Tomogr

1981;5:851-854 surgical

6. Aosai J, ed. Ackerman’s 1989:875 7. Lieber MM, 1981;125:481

Tomera -485

8. Quinn MJ, Hartman observations.

Radiology

KM,

Farrow

pathology, GM.

7th ed. St. Louis, Renal

oncocytoma.

D5, Friedman AC, et al. Renal oncocytoma: 1984;1 53:49-53

Mosby, J

Urol

new