AJR 2000; 175:883-884
© American Roentgen Ray Society
Genitourinary Case of the Day |
Case 2
Angiomyolipoma with Minimal Fat Content
William F. Bennett,
James G. Bova and
Kuldeep Vaswani
Although these images (Fig.
2A,2B,2C,2D)
do not represent the typical appearance of an angiomyolipoma because there is
no fat within the mass on this scan, this is the preferred diagnosis over the
other choices. The images are nonspecific; this lesion could represent any of
the solid tumors, such as renal cell carcinoma, oncocytoma, or tumors of
mesenchymal origin. A retroperitoneal hemorrhage from a renal mass in a young
patient would suggest an angiomyolipoma. Percutaneous biopsy of this mass
revealed a mixture of mature adipose tissue, spindle cells, and plump
epithelioid cells consistent with an angiomyolipoma. An image of the right
kidney above this level (Fig.
2D) shows a typical small
angiomyolipoma.
View larger version (121K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2A. —21-year-old man who presented with retroperitoneal hemorrhage at
outside institution and underwent follow-up CT 1 week later. Unenhanced CT
scan shows low- to intermediate-density mass (arrow) before contrast
material administration.
|
|
View larger version (134K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B. —21-year-old man who presented with retroperitoneal hemorrhage at
outside institution and underwent follow-up CT 1 week later. Contrast-enhanced
CT scans show mass has enhanced with uniform heterogeneity
(arrows).
|
|
View larger version (130K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C. —21-year-old man who presented with retroperitoneal hemorrhage at
outside institution and underwent follow-up CT 1 week later. Contrast-enhanced
CT scans show mass has enhanced with uniform heterogeneity
(arrows).
|
|
View larger version (143K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D. —21-year-old man who presented with retroperitoneal hemorrhage at
outside institution and underwent follow-up CT 1 week later. CT scan of small
fatty lesion (angiomyolipoma) of right kidney (arrow).
|
|
Retroperitoneal hemorrhage usually has a higher density on the unenhanced
CT examination, although there may be some decrease in density with time.
However, regardless of the age of the hemorrhage, it should not enhance on the
contrast-enhanced scans. In addition, the margin of the lesion is very
discrete. Spontaneous retroperitoneal hemorrhage is seen in patients who are
undergoing anticoagulation therapy. Spontaneous retroperitoneal hemorrhage
commonly occurs in the psoas muscle. Angiomyolipoma is another source of
bleeding.
Psoas abscess is incorrect. Abscesses contain fluid. Even if there is a
sufficient amount of protein present to increase the density, the avascular
fluid does not increase in density with contrast administration. Psoas
abscesses are caused by postoperative infection or extension from
discitis.
Multilocular cystic nephroma is incorrect. This benign tumor of the kidney
is predominantly cystic with multiple fine septations that may give a ground
glass appearance. Though some components of this tumor can enhance, most of
the tumor does not.
Angiomyolipoma is a benign tumor that is characterized by its fat content,
and it may contain calcifications. Angiomyolipoma is commonly seen in patients
with tuberous sclerosis but may arise sporadically without the syndrome. Small
angiomyolipomas are of low clinical significance and have no malignant
potential. Larger lesions are also benign but may cause life-threatening
retroperitoneal hemorrhage, as in this case.
Before the advent of CT, these lesions were surgically removed because they
had the urographic and angiographic appearance of renal cell carcinoma. On CT
a lesion that has predominantly fatty density is diagnostic of an
angiomyolipoma. There have been case reports of renal cell carcinomas and
oncocytomas that engulfed small collections of fat
[1,2,3].
Though this is rare, the presence of fat may give an incorrect diagnosis.
Rarely, angiomyolipomas can have minimal fat content. Jinzaki et al.
[4] reported six such cases. In
their series, 5% of angiomyolipomas had minimal fat content. The incidence is
probably less than this, considering there are few case reports in the
literature. The homogeneous enhancement and the presentation of
retroperitoneal hemorrhage in a young man prompted the percutaneous biopsy in
this case.
References
-
Hammadeh MY, Thomas K, Philp T, Singh M. Renal cell carcinoma
containing fat mimicking angiomyolipoma: demonstration with CT scan and
histopathology. Eur Radiol
1998;8:228
-229[Medline]
-
Strotzer M, Lehner KB, Becker K. Detection of fat in a renal cell
carcinoma mimicking angiomyolipoma. Radiology
1993;188:427
-428[Abstract/Free Full Text]
-
Miltner P. A spontaneously ruptured renal oncocytoma: fat inclusion
simulating an angiomyolipoma [in German]. Rofo Fortschr Geb
Rontgenstr Neuen Bildgeb Verfahr
1999;170:325
-326[Medline]
-
Jinzaki M, Tanimoto A, Narimatsu Y. Angiomyolipoma: imaging
findings in lesions with minimal fat. Radiology
1997;205:497
-502[Abstract/Free Full Text]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
