General Joseph
Case
Casullo,
MD
of the
#{149} MaxJ.
Day1
Palayew,
MD
#{149} Andre
Lisbona,
MD
4
b. Figure 1. Posteroanterior (a) heart and extending posteriorly, cardiac silhouette (arrowheads
U HISTORY An asymptomatic gated for abnormal ings
(Fig
1) that
and lateral simulating in b).
(b) chest radiographs show a large soft-tissue mass overlying the an elevated left hemidiaphragm (arrows in b). Note the normal
78-year-old man was chest radiographic had
not
changed
the posteroanterior projection, although a normal silhouette was seen on the lateral view. The lateral radiograph showed the mass extending posteriorly and simulating an dcvated left hemidiaphragm. The contrast-enhanced CT images revealed a mass of almost homogeneous fat attenuation (120 to - 130 HU) occupying the entire left lower hemithorax (Fig 2). At higher levels, the mass draped around the left border of the heart and appeared to originate in the antenor mediastinum. There was slight displacement of the carmna and the descending aorta toward the right, with no evidence of invasion of mediastinal structures. The mass contained a few linear areas ofhigher attenuation. On the Ti-weighted MR images, the mass had homogeneously high signal intensity (Fig 3), as might be expected from its fatty appearance on the CT scans.
investifind-
significantly
compared with those from previous studies dating to when he was 25 years old. At that time, he had also been entirely asymptomatic. Computed tomography (CT) with contrast material enhancement (Fig 2) and magnetic resonance (MR) imaging (Fig 3) were performed. U FINDINGS The posteroanterior and lateral chest radiographs demonstrated a large soft-tissue mass overlying the heart (Fig 1). The mass mimicked a greatly enlarged cardiac sithouette on
Index
terms:
Lipoma
RadloGraphics I
From
1992;
the
21; accepted 3755 Cote C RSNA.
1250
U
Department
and
lipomatosis,
676.319
#{149} Thorax,
neoplasms.
676.319
#{149} Thymus,
neoplasms,
676.3
19
12:1250-1254 of Radiology.
McGill
University.
August 24. Address reprint requests St Catherine Rd. Montreal. Que, Canada
Montreal. to MJ.P.. H3T 1E2.
Received
Department
July
2 1 . 1992;
of Radiology.
revision Sir Mortimer
requested
July
B. Davis-Jewish
28 and
received
General
August Hospital.
1992
Ra4ioGrapbics
U
Casullo
et 31
Volume
12
Number
6
r’ t
\L....:
..
3. Figures 2, 3. and containing of homogeneous
..
. .
:#{149}‘ .
(2) Contrast-enhanced a few strands of higher high
signal
intensity,
CT scans attenuation similar
show a diffusely fatty mass (arrows). (3) Ti-weighted
to that
filling
the left lower
hemithorax
MR images demonstrate fat, along the anterior chest
of subcutaneous
wall
a mass (ar-
row).
DIAGNOSIS: U
tumor mass of lymphocytes
Thymolipoma.
DISCUSSION
Thyrnolipomas thymus
gland
are and
rare, account
benign for
tumors 2%-9%
of the of all
thymic tumors (1,2). These tumors are composed of lobules of mature fat and scattered islands of normal thymic tissue. The latter constitute from less than 10% to 33% of the
November
1992
(2,3).
The and
thymic
tissue
characteristic
consists whorls
of
epithelial cells known as Hassall corpuscles (Fig 4). The lobules of fat are separated by fine strands of connective tissue. Grossly, thymolipomas are lobulated, pliable, encapsu-
Casullo
et
31
U
RadioGraphics
U
1251
a.
b.
Figure 4. (a) Gross specimen of a large thymolipoma removed from a 22-year-old man whose chest radiographs are shown in Figure 5. The tumor is yellow, smooth, and lobulated, with a thin capsule covering the entire mass. (b) Photomicrograph (original magnification, X 350; hematoxylin-eosin stain) of the tumor reveals mature fat cells and focal areas of normal thymic tissue, shown here with Hassall corpuscles.
lated tumors capable of growing to a very large size. In the majority ofcases (70%), these lesions weighed over 500 g and 20% weighed over 2,000 g (1,4). The largest reported tumor weighed over 16 kg (1). Thyrnolipomas occur with equal frequency
phragm and may drape around the heart or insinuate themselves between the lungs and the mediastinum, the heart, and the diaphragrn (2,6). On plain chest radiographs, these large thymolipomas produce abnormal
in men
megaly lateral
and
is 22 years,
women.
The
although
the
mean age
age
opacities
of patients
range
is quite
wide (3-60 years). Fifty percent of patients with thymolipomas have symptoms that are related to compression of mediastinal structures by the tumor mass. Chest pain, dyspnea, and cough are the most frequent complaints. Rarely, thymolipomas may occur in associa-
tion
tion
with
sis
and
Graves
tients,
myasthenia
disease
thymolipomas
gravis,
(4).
aplastic
anemia,
In asymptomatic
are
usually
pa-
discovered
incidently on routine chest radiographs, as in our patient. Some patients with thyrnolipoma have had abnormal chest radiographs dating back to over 10 ther invasion of nant transformation mented. These to the pleura or sion
years before surgery mediastinal organs have ever been tumors may adhere, pericardium. Surgical
of thymolipomas
is curative.
Smaller thyrnolipomas usually fined to the anterior mediastinum indistinguishable
anterior sions
tend
remain and
radiographically
mediastinal to slump
(5). Neinor maligdocuhowever, cxci-
masses inferiorly
conare
from
(6).
other
Larger
toward
lethe
dia-
that
may
on the projection of the
diaphragm
of a fatty
the periphery olucent than may
be
lesion
RadioGraphics
U
Casullo
Ct
31
for
cardio-
and
a clear
superior
can
be
entertained
when
of the mass appears its bulky center (6,9).
better
illustrated
on
more This
radisign
well-penetrated
radiographs obtained with a Bucky grid. However, a clear peripheral zone is not specific for thymolipoma, because a similar finding has also been observed in connection with mcdiastinal
lipoma
(9).
In the majority of cases, the CT appearance of thyrnolipomas is that of sharply defined, predominantly fatty masses containing interspersed strands of soft-tissue attenuation presumed to represent thymic tissue and fibrous stroma (5, 10-13). As described in one case report, thymolipomas having such an appearance on CT scans would be mostly high in intensity
low-signal-intensity
U
mistaken
retrosternal space when the masses extend posteriorly (6). Radiographically, large thyrnolipomas may also mimic basal atelectasis, large pleural or pericardial tumors, or pulmonary sequestration (6,8). Occasionally, the diagno-
signal
1252
be
frontal view (Fig 5) (6,7). The may show apparent eleva-
and
would
contain
strands
on
(12).
Thymolipomas
may
tively
homogeneous
on
also CT
and
scattered MR
images
appear MR
Volume
relaimages.
12
Number
6
a.
b.
Figure 5. Thymolipoma anterior radiograph (a) clear retrosternal space.
in a 22-year-old and an elevated
asymptomatic left hemidiaphragm
Two cases of thymolipomas have been described in which the preoperative diagnosis had been mediastinal lipoma based on the almost uniform fat attenuation seen on CT scans in one case (7) and the uniformly high signal
intensity
seen
ond case of thymic
(14).
less
10%
than
on
MR
As mentioned,
tissue
in some (2),
images
in the
the
proportion
thymolipomas
which
may
not
5cc-
can be
be
visual-
ized on CT and MR images. have been proposed about of thymolipomas. According thymolipomas may represent
Many theories the pathogenesis to one theory, enlarged hyper-
plastic
thymic
sia)
thymus whose
glands thymic
volution
with
element speculative,
continues the
neity
of these
(true component
time
while
hyperpla-
undergoes
the
in-
lipomatous
to grow (1,15). Although variable degree of mnhomoge-
lesions
on
CT
and
MR
images
observed among different patients may reflect the different stages of thymic involution. The differential diagnosis oflarger thymolipomas includes mediastinal lipoma and liposarcoma. The former is the most common of the intrathoracic lipomas and shares many clinical and radiologic features in common with
thymolipoma
(16,17).
About
75%
of re-
ported mediastinal lipomas were found in the anterior mediastinum, in which the area of the cardiophrenic angle was the most frequent site ofoccurrence (18). Some lipomas, however, can attain enormous dimensions and extend into all compartments of the mediastinum and the adjacent hemithorax along
November
1992
man
simulates (arrowheads)
cardiac enlargement on the posteroon the lateral view (b). Note the
the diaphragm. A mediastinal lipoma, therefore, could not be entirely excluded as a diagnostic possibility in our case. Liposarcoma, however, is an unlikely diagnosis. Although the well-differentiated liposarcoma can behave in a relatively benign fashion (19), it would be extremely unusual for such a tumor to remain dormant for 50 years. Furthermore, even well-differentiated abundant mature display scans,
an
liposarcomas with tissue generally
adipose
mnhomogeneous
demonstrating
pattern CT
on
numbers
than those ofnormal fat (20,2 1). Our patient, a physician, was told years
that
he
had
cardiomegaly
CT
greater
(on
at age the
25
basis
of the initial chest radiograph). Being asymptomatic, he refused further investigation. Following our diagnosis of thymolipoma, when we saw him some 50 years later, he agreed to undergo CT and MR studies. U 1.
2.
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