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.

REFERENCES Rosai J, Kevine GD. Tumors In: Atlas of tumor pathology, Washington, Pathology, Marchevsky

the thymus.

3.

DC: Armed 1976; 162-166. AM, Kaneko

Surgical

Forces M.

pathology

of the thymus. fasc 13, ser 2. Institute Other

of

tumors

of

of the medias-

tinum. 2nd ed. NewYork: Raven, 1992; 152154. Iseki M, Tsuda N, Kishikawa M, et al. Thymolipoma with striated myoid cells. AmJ

Surg

Pathol

Casullo

1990;

et 31

14:395-398.

U

RadioGraphics

U

1253

4.

Otto

HF,

Loning

RWC, Gurtler

in association with 1982; 50:1623-1628. Nishimura 0, Naito

5.

Takenaka 6.

Lachenmayer L, Janzen K. Thymolipoma myasthenia gravis. Cancer

K.

Y, Noguchi

Thymolipoma:

cases.JpnJ

Surg

TeplickJG,

Nedwich

1990;

Y, Matsuoka

a report

5,

of thymolipoma.

10.

1 1.

AiR

14.

15.

puted

Raven,

19.

BA. of

U

RadioGraphics

U

Casullo

et 31

Cardiovasc lipomas

tomography.

ed. New

relationship

be-

and the thymus.

J

27:494-502.

Funahashi

Yl, Kalyoncu

The

Magnetic

2nd

A, GehlsenjA, H.

Intrathoracic

Surg

1979;

AF, Aydiner

DeCock lipomas. 77:550-556. A, et al. In-

demonstrated

Respiration

D, J

by com-

1990;

57:77-

80. Pachter MR, Lattes R. Mesenchymal tumors of the mediastinum. Cancer 1963; 16:74-94. Schweitzer DL, Aguam AS. Primary liposar-

coma

of the mediastinum.

J Thorac

Cardio-

Surg 1977; 74:83-97. Mendez G Jr, Isikoff MB, Isikoff 5K, Sinner WN. Fatty tumors ofthe thorax demonstrated byCT. AiR 1979; 133:206-212. Lee JK, Sagel SS, Stanley RJ. Computed body tomography with Mifi correlation. 2nd ed. New York: Raven, 1989; 745-746. vasc

20.

2 1.

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CA.

of the body. 473-474.

lipomas

1954;

BF, Choi

trathoracic

18.

AiR 1983; 140:1131-1133.

Surg

PolitisJ,

Bans

DV, Marcomputed

Pediatr

H, Helms

mediastinal

Thorac 17.

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imaging

Raven, 1992; M, Mishkin S.

Stengel

Naidich DP, Zerhouni EA, Siegelman 55. Computed tomography and magnetic resonance of the thorax. 2nd ed. New York: 1991; 35-148.

York: Rubin

RK, Schidlow Thymolipoma:

appearances. CB,

Thorac

16.

thymolipoma.

Higgins

tween

A.

Yeh HC, Gordon A, Kirschner PA, Cohen Computed tomography and sonography

F, Gold-

20: 196-197.

resonance

L, Oz M, Davies

MH, Eftekhari

Faerber EN, Balsara mon LM, Zaeri N. 1990;

Roent-

Thymolipoma simulating pulmonary sequestration. J Pediatr Surg 1982; 17:313-3 15. Heuer GH. I’he thoracic lipomas. Ann Surg 1933; 98:801-809.

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tomographic

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Matsuyama K, Nakagawa T, Horio Y, Hongo H, Miyauchi Y, Yasue H. Thymolipoma simulating cardiomegaly: diagnostic usefulness of computed tomography. Jpn Circ J 1986; 50:

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KF, Fischer

Volume

12

Number

6

General case of the day. Thymolipoma.

General Joseph Case Casullo, MD of the #{149} MaxJ. Day1 Palayew, MD #{149} Andre Lisbona, MD 4 b. Figure 1. Posteroanterior (a) heart an...
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