From

the of the

Archives This article

meets the 1.0 credit in Category 1 of

critertafor

hour theAMA

Thyinoma:

AFIP

Radiologic-Pathologic

Correlation

Physician’s

Recognition Award. To obtain credit, see the questionnaire at the end oftbe article.

Melissa CesarA.

L. Rosado-de-Christenson, Moran, Maf, USAF,

Thymoma

most

is the

of thymomas

ity

frequently, tinal

common

The usual

found

incidentally

mass

features

may

sites.

of thymoma

radiologic

rounded,

and

mediastinal

mass structures

jacent

complete nosis

of encapsulated

with

exhibit

presentation

is that

most

common

superior

excision.

Radiation in the

thymoma

therapy

medias-

variable

gross

in a variety

in the treatment

a prevascular

evaluation of adof choice is

chemotherapy

favorable.

may be

tumors. Invasive

but may respond

of

is a

Computed

show

of invasive

is generally

prognosis

The

result

Less

metastasize

mediastinum.

and

treatment

major-

manifestation

typically

of variable size and may be helpful in cases of invasive thymoma. The to surgery

may

of an anterior

invasion

imaging

The

behavior.

they

radiologic

of the anterior

thymus.

patient.

for local

resonance

a worse

MD

a benign

or rarely

in an asymptomatic

mass

surgical

adjunctively

Galobardes,

of the

and

invasive,

the potential

magnetic

used

associated

be locally

The

soft-tissue

tomography

#{149} Josefa

neoplasm

masses

clinical

and

appearances.

MC

USAF,

primary

are encapsulated

thymomas

to distant

Maf, MC

to radical

The

prog-

tumors

are

resection.

INTRODUCTION

U

Thymomas are epithelial neoplasms of the thymus and the most common primary neoplasms of the anterior superior mediastinum. They usually occur in adults. The tumor may be completely encapsulated or may display various degrees of invasion of the tumor capsule and the adjacent structures. In this article, we review the histologic types and gross features of thymoma as well as its clinical presentation, therapy, and prognosis. The various radiologic featunes

of thymoma

Abbreviation: Index

PA

terms:

RadioGraphics From Forces Radiology, formed received requests

RSNA,

=

illustrated

with

Thymus,

CT,

1992;

12:151-168

Hospital Services

676.121

1 #{149} Thymus,

de Getafe,

Universitanlo University

October

emphasis

on nadiologic-pathologic

correlation.

posteroanterior

the Departments of Radiologic Pathology Institute ofPathology, Bldg 54, Rm M-121,

28; accepted

of the

Health

October

MR. 676.

(M.L.R.) Alaska

Madrid

Sciences 30. J.G.

1214

#{149} Thymus,

and Pulmonary and Fern Sts,

0G.); (M.L.R.).

supported

and

neoplasms,

676.3154,

676.3155

and Mediastinal Pathology Washington, DC 20306-6000;

the Department

Received

August

by Fondo

de

of Radiology 28;

revision

Investigaci#{243}n

and

requested Sanitania,

(CAM.), Armed the Department Nuclear

Medicine,

September Spain.

Address

of Uni-

27 and

reprint

to M.L.R.

The opinions or as reflecting C

are

and assertions contained herein are the private the views of the Department of the Air Force

views or the

of the Department

authors

and

are

not

to be construed

as official

of Defense.

1992

151

The

anterior-superior

mediastinum

compartment

is the

most

mediastinal neoplasms is the most common in this location (1).

men

and

women

with

Thymoma

uals

50%

incidentally because

been

adults

Approximately

covered

of pni-

gravis

equal

reported

and

rarely

of thymomas in asymptomatic

nia gravis

of nadiographs

essanily

obtained

fre-

disindividfor

other reasons. In 25%-30% of cases, patients present because of signs and symptoms nelated to compression of adjacent mediastinal structures. Compression of the trachea, the recurrent laryngeal nerve, on the esophagus may

produce

pinatory

cough,

Patients

may

signs

chest

hoarseness,

present

related

cent

dyspnea,

infection,

with

nia gravis

thymoma

or other

red cell aplasia,

mia,

endocrine

dens,

and

tissue

conditions

have

parathymic

syndromes

proximately

40%

Primary

nia

gravis

des.

and

to be

den in which antibodies receptors interfere with Thymic

nia

gravis.

The

mic

abnormality

sia,

seen

with

hyperplasia but

does

follicles

not

within

necessarily

with

myasthe-

found

in

PATHOLOGIC

.

Microscopic

U

thy-

thy-

thymus

Rosado-de-Christenson

primary

epithelial

be completely

neoplasms

encapsulated

on locally

thymomas

a thick

fibrous

ferned

over

moma

is a separate

malignant

are

capsule.

thymoma.

entity

Histopathologically,

hyperpla-

in thymic

Characteristics are

within

fled according

con-

Invasive

from

Invasive

carci-

malignant epithelial

thymomas

to predominant

thy-

thymic

are

cells. classi-

cell type:

bi-

phasic thymomas (epithelial and lymphoid elements are present in roughly equal

gland

amounts),

mas

en-

et a!

predominantly

(at least

epithelial)

RadioGraphics

have

FEATURES

Encapsulated

momas

U

5% of pa-

hypogammaglobulinemia

U

phocytes),

152

thymoma

and

noma, which is a histologically neoplasm arising from thymic

myasthe-

65% of patients Follicular thymic by the presence the

with

thymomas are histologically identical to encapsulated thymomas but have microscopic evidence of growth outside the tumor capsule. Because histologic features of malignancy (eg, high mitotic activity, prominent nucleoli, and nuclear hypenchromasia) are absent, the term invasive thnoma is pre-

mus-

with

result

of patients

(5).

fined

dison-

thymic

(5).

is characterized

oflymphoid

also

associated

is follicular gravis

thymoma

been (2,5).

are

common

with

invasive.

against acetylcholine neuromuscular trans-

in approximately

myasthenia

thymoma.

autoimmune

of patients

most

10%

hypogammaglobulmnemia,

that can

characterized

abnormalities

90%

approximately

characterof marrow

Thymomas

to as

of skeletal an

dis-

as

Myasthenia

fatigability

on after

Red cell aplasia is a rare disorder ized by an almost total absence

have

in ap-

have

disorder

It is thought

mission.

with

established.

is well

before

develop after (2,5,6). red cell aplaestablished.

Approximately

These

found

with

Myasthenia

diagnosed

covery of a thymoma, or it may surgical excision of a thymoma An association between pure sia and thymoma has also been

moma

referred

are

synchronously. be

have myasthedo not nec-

disor-

disorders.

of thymoma

is a neunologic

by weakness

such

neoplasms

relationship

gravis

disorders,

of patients

in association

The

myasthe-

been

and

malignant

described

have

cutaneous

connective

associated

and

hypogammaglobuline-

disorders,

may

tients

may

systemic

pure

res-

adjasuch as supeRarely, sudden to be secondby the tumor,

structures, non vena caval syndrome (4). cardiac death, which is thought ary to right atnial compression may occur (2).

15% of myassetting of 7%-

in approximately

and blood reticulocytes that nesuits in severe normochnomic, normocytic anemia. This disorder may be mediated by a humoral immune response where a serum immunoglobulin G enythropoietic inhibitor may be responsible. Approximately 50% of patients with red cell aplasia have thymoma. Conversely, approximately 5% of patients with thymoma have red cell aplasia (5,6). Thymomas have also been associated with adultonset, acquired hypogammaglobulinemia.

of the

candiovasculan

Patients

pain,

symptoms

invasion

thymic

erythroblasts

or dysphagia.

with

to tumor

common

of myasthenia

with thymoma The two conditions

(5). occur

gravis

in chil-

are

is found

of patients

54%)

less

very

and

is a less

the setting

in

patients with this disease. In contrast, thenia gravis is more common in the thymoma: Approximately 35% (range,

of affected patients of age, and 70% of and 6th decades of

has

quently in young dren (3).

site

Thymoma

abnormality

or cysts. Thyprimary neoplasm The tumor affects

approximately

The majority are adults oven 40 years tumors occur in the 5th frequency.

(2).

of the

common

mary moma found

life

largement.

PRESENTATION

CLINICAL

U

two-thirds and

(at least

lymphocytic

of the cells

predominantly

two-thirds

thymo-

are lym-

epithelial

thy-

of the cells

are

(7).

Volume

12

Number

1

.

.‘r.

j:’. ‘:; ..\

-.

#{149}

: ‘‘.

..

,‘,,

;.

:

.

,.:?‘

‘:

. ,.

.

.

..:



:

,

.

I’:

1.



.

:

.‘.\#{149}.

....

.#{149}..\i

.

.

.

;.

a.

b. Figure

.1

..

:;



#{149}

....

...

1j

1.

Biphasic

Low-power phox 30; hematoxylin-eosin [H-El stain) shows tumor lobules sep. arated by fibrous septa (arrows). (b) High-power view (original magnification, x 1,050; H-E stain) shows two populations of cells-lymphocytes (straight arrows) and epithelial cells (curved anrows)-in roughly equal proportions. (c) Lowpower view (original magnification, x 75 ; H-E stain) shows cystic spaces filled with hemorrhage and amorphous material (arrows). tomicrograph

‘,..

thymoma.

(original

.,

should

lead

nosis

the

examiner

oflymphocytic

least

thymomas

and

are the most magnification,

contain

epithelial

angulated

an

cells

admixture

arranged

bonders

(Fig

la).

with

lobules

are

guish

be

calcified.

The

epithelial

composed of polygonal cells fined bonders; clear cytoplasm;

round

to oval nuclei

component

with

(Fig ib).

and

be difficult obtained. capsule,

January

1992

lymphomas,

when

and

a small

the

biopsy

well-desingle,

may

be

are

have

the

characterized

this

variant

tumor

the

classic by

of thymoma

mas

is cyst

be seen are

and (Fig

is necessary

help

and

establish

(2,7,8).

of some thymobe microin approximately 40% of Cysts

more

may

commonly

seen

in lange

may represent degenerative ic). Careful histologic evaluation when

areas

a

characteristic

formation.

can

thymomas,

tumors, change

features

diagnosis

specific

scopic,

tumoral

techniques

microscopy

correct

One

and

or hemangiopenicy-

Immunohistochemical

electron the

The lymphoid

distinction

between

toma. is

cells admixed with the epithelial cells are small, mature lymphocytes with small dank nuclei and scanty cytoplasm. Mitoses may be seen in the lymphoid component. Predominantly lymphocytic thymomas must be distinguished from well-differentiated lymphocytic

thymomas

They

on may

fibnohistiocytic

separated by thick fibrous bands that often are contiguous with the tumor capsule, which may

diag-

cells arranged in a storiform patnumerous thin-walled blood vessels mimicking a vascular or fibnohistiocytic tumon. The latter thymomas are called spindle cell thymomas. It may be difficult to distin-

of lymphoid

The

type. cells

correct

elongated tern, with

common. these

in lobules

epithelial

common

epithelial

to the

thymoma.

Predominantly C.

Biphasic thymomas As seen at low-power

(a)

magnification,

may

the

not

cysts

are

be readily

lange,

seen

since

the

(9).

may

specimen

is

However, the presence of a thick fibrous bands, or a calcified capsule

Rosado-de-Christenson

Ct a!

U

RadioGrapbics

U

153

. Gross Because

Characteristics the normal thymus

junction

of the

dium,

most

great

vessels

and

thymomas

are

closely

these structures. variable location can occur in any tion,

from

is adjacent

the

the

Encapsulated thymomas may have fibrous adhesions to adjacent mediastinal structures, the pleura, and the chest wall. These fibrous

to the pericar-

related

adhesions,

to

However, because of the of thymic tissue, thymomas anterior mediastinal loca-

thoracic

inlet

to the

variability

in size has been

grow.

The

tumor

smooth or lobulated, tan or grayish pink

The

tumor

visible

is divided

fibrous

into

bands

mon substance

surface

may

from

that

lobules

into

into

the

variable

scopic

residual

examination

areas

cases,

of the

of thymoma

careful

U

RadioGraphics

U

tu-

U

the

diagno-

of thymomas

may

grow

through

structures.

are the

the surrounding

growth

tu-

mediastinal

Local

of invasive

abdomen

has

STAGING

Staging

OF

invasion

of

of of

also

thymomas

been

described

sites kidneys,

THYMOMA

of thymoma

on absence

is based

of an intact

tumor

on

the

presence

capsule.

Staging

of minimally invasive croscopic examination tumor and suspected

thymoma requires miof the periphery of the sites of local invasion.

Two

systems

different

staging

are currently

used.

In the simplest, I refers to lesions

micro-

rounded tumors capsule

oldest staging system, stage that are completely sun-

tumor capsule. Stage II of growth outside the mediastinal fat, without invasion of adjacent mediastinal structures. Stage III tumors show invasion of mediastinal structures or other adjacent structures, such

wall reveals (7, 10) (Fig 4).

cyst

Rosado-de-Christenson

adjacent

the

as the

154

to make

of histo-

(10).

(12). Metastases to distant extrathoracic such as the liver, bone, lymph nodes, and brain occur infrequently (5,10,13).

by grossly The

In the latter

into

aphragmatic

is soft.

extend

with

dium, and the heart may also occur. Thymomas may extend into the subpleural space or may manifest as pleural tumor implants. In these instances, thoracic involvement by the tumor is usually unilateral (4, 10, 1 1). Transdi-

be

the capsule.

confirmed

in-

the pleura occurs most frequently. Invasion the adjacent lung is less common. Invasion the mediastinal blood vessels, the pericar-

size of the tumor lobules gives rise to the external lobulated or bosselated appearance of the mass (2,7) (Fig 2). Areas of hemorrhage and necrosis may occur within thymomas and may progress to form macroscopic cysts with fluid content ranging from clear to thick hemorrhagic matenial (Fig 3). The cysts vary in size and occasionally may be the dominant component of

the tumor.

mon capsule

not

evidence

one-third and

are

Gross

of invasion

invasive

fat and

be

thymoma

Approximately

reported,

and the cut surface and characteristically

evidence

truly

at surgery,

invasion. always

sis of invasive

ranging from small tumors measuring a few millimeters to very large tumors measuring up to 34 cm in widest diameter. The majority of thymomas range from 5 to 10 cm in size (7). Thymomas are usually round on ovoid masses that deform the surface of the thymus as they

must

logic

cardio-

noted

of tumor

invasion

phnenic angle. Thymomas have been found in the neck and rarely in other mediastinal compartments, the lung parenchyma, and the tracheobronchial tree (2,7). Most thymomas are slow-growing tumors.

Great

often

dicative

et a!

by an intact show evidence and into the

lung,

pleura,

subpleural

space,

Volume

and

12

Number

1

3.

4.

Figures 2-4. Encapsulated lobe. (2b) Close-up view septa. Septa are contiguous

thymoma. (2a) Resected thymus contains a rounded lobulated mass in the left of the cut surface of the thymoma shows the tumor lobules surrounded by fibrous with the capsule. (3) Cut surface of an encapsulated thymoma shows central an-

eas of hemorrhage, necrosis, and cystic change. (4) Cut surface of an encapsulated, predominantly Septations

arise

from

the

inner

wall

of the

chest wall. Seeding of the pleural distant metastatic spread are also stage III disease (7).

tem

A more recent, more has been proposed

leagues

thymomas invasion.

January

1992

(14).

In this

Stage

II tumors

system,

without show

cavity and included in

stage

capsular microscopic

of the tumor (arrows). have been evacuated.

cyst.

complex staging by Masaoka and

staging

are also those

The capsule is seen in the periphery cystic thymoma after cyst contents

syscolI

invasion

of the

capsule,

adjacent

mediastinal

fat, on surrounding pleura. Stage III lesions invade surrounding organs and structures such as the lung, penicardium, superior vena cava, and aorta. Stage Na refers to dissemination in the thoracic cavity, and stage IVb refers to distant metastases (14). We use this staging system

in this

Rosado-de-Christenson

article.

et a!

U

RadioGrapbics

U

155

Figure 5. Encapsulated thymoma in a 53-year-old woman (a) Posteroanterior (PA) chest radiograph shows a left-sided, ders.

(b)

opacity

On in

the chest

lateral

the

shows

attenuation

Outer

central

necrosis

.

radiograph, space.

the mass

of the

change.

U

chest

retrostemal

located

periphery

borders

the (c)

RADIOLOGIC

is seen

of the

mass

central

area

ofdecreased

that

other

hemithonax.

extend

to both

Linear

shows

scan

of

increased

of cystic

ovoid

tumor

one

on the

with

on c.

protrude

into

Less commonly,

they

sides of the midline (Fig may occur in the candiophnenic

may 6).

Thymomas

range from small, subtle, abnormal mediastinal opacities to large, anterior mediastinal masses. In the absence of local invasion, the

ment on frontal radiographs (Figs 7, 8). On lateral nadiographs, they may be visible as a rounded, soft-tissue opacity in the retnoster-

masses

nal clean

lung

U

masses

seen

artery. suggestive

specimen

soft-tissue (CT)

The radiographic appearance of thymoma is frequently that of a contour abnormality of the mediastinum. Radiographic abnormalities

displace

the

panietal

and

visceral

pleu-

ral surfaces, resulting in smoothly marginated, often lobulated bonders against the adjacent

156

tomographic

attenuation

ofgross

attenuation

eral

Appearance

computed

decreased

(d) Cut surface

FEATURES

Radiographic

as an abnormal

of the pulmonary

to the root

with

pain, cough, and fatigue. mass with smooth bor-

mediastinum

anterior

is seen,

to the

anterior axial

are lobulated.

corresponds

in the

and shoulder mediastinal

material-enhanced

immediately

of the mass

(*) that

mass

Contrast

with back rounded

(Fig

RadioGrapbic.s

5). Thymomas

U

are

commonly

Rosado-de-Christenson

angle,

on they

may conform

cardiac

bonder,

simulating

tinal

space

location

may manifest these cases,

unilat-

et

a!

or in another (15)

(Figs

as very large the mediastinal

to the adjacent cardiac

Sb,

enlarge-

anterior medias7, 8). Thymomas thoracic masses. In on thymic origin

Volume

12

Number

1

a.

b.

d.

C-

f_ a history

C-

Figure

6.

radiograph

the mass tion

of the

component bibbed

thymoma

shows

mediastinal

occupies

projects

cation

Encapsulated

to the mass

(arrow). mass

of the

a large

the left superior right

and

in the

in a 22-year-old mass the

right

mediastinum.

mediastinum.

with to both

and has a thin, cardiac The

(c) Axial contrast-enhanced anterior

projects

mediastinum

silhouettes

anterior

that

man

CT scan Rim

border.

calcified

rim

sides

linear (b) is seen

ofleft-sided of the

and

internal

pain.

The

Lateral

chest

along

(a) PA chest

superior

rim ofcalcification.

The

periphery

shows of

pulmonary

decreased

portion

inferior

radiograph

the

at the level of the right

calcification

chest

midline.

the

artery

attenuation

are

of

porthe

lo-

superior shows

a

seen

in

the left portion of the mass. (d) Axial contrast-enhanced CT scan at the level of the left atrium shows the middie portion of the mass, partially surrounded by a thin arc of calcification. (e) Transverse sonogram through the inferior aspect of the mass shows multiple small cysts within the lesion. At surgery, an encapsulated, pear-shaped thymoma was found. (f) Cut section shows necrotic component of the superior aspect of the

January

mass,

corresponding

rionly

and corresponds

1992

to the

area

to one

of decreased

of the cysts

attenuation

seen

seen

at CT. A small

cystic

area

(arrow)

is seen

infe-

sonographically.

Rosado-de-Christenson

et a!

U

RadioGraphics

U

157

,

-

7a.

7b.

-.

8a. Figures

7, 8.

infection.

(a)

borders.

(7) Encapsulated PA chest

(b) Lateral and

thymus

was

graph

shows

houettes gin of the

chest (8)

a large,

RadioGrapbics

1-year-old

mass

that

thymoma

man

of the

the mass

encapsulated

to determine

mass Lateral

of the

that conforms

radiographs.

is commonly

The linear,

thin,

Rosado-de-Christenson

of and

tract

sharp,

lobulated

(jrojecting aspect

of the

right

woman.

(a)

PA chest

to the right the

over

cardiac

the cardiac lobe

border

posterior,

of the thymus

of the

radio-

and

smooth

sil. mar-

was found.

(2).

Invasive thymomas tunes similar to those An irregular interface

be de-

pattern

respiratory

with

located

radiograph shows of the right lobe

the tumor may

angle

nipheral and corresponds to calcium deposition in the tumor capsule (Fig 6). Calcified foci may also be seen scattered throughout

(Fig 9). Patients with have entirely normal a thymoma

of upper

inferior

asymptomatic

chest thymoma

with

symptoms

cardiophrenic

is anteriorly

in a 36-year-old

mediastinal

with

night

thymoma

cardiac enlargement. (b) At surgery, an encapsulated

may be difficult

U

a large

shows an

smooth-bordered,

simulating mass (arrow).

on plain

calcification

radiograph

Encapsulated

it,

in a 5

shows

At surgery,

radiographic studies small thymomas may chest radiographs. Calcification within

tected

thymoma

radiograph

rounded.

found.

of the mass

U

-

8b.

silhouette)

158

.

pe-

et a!

have radiographic of encapsulated with the adjacent

Volume

featumors. lung

12

is

Number

1

a.

b.

d.

C.

9.

Figure

shows

Thymoma

a huge

radiograph

length

lobulated shows

resonance signal intensity

January

smooth

of the chest.

netic

the tumor

1992

in a 44-year-old

lobules

There

mass

with

an upper

of the left hemithorax

superior

is complete

(MR) image shows and the suggestion

seen

man border

of the

silhouetting that the of tumor

with mass,

respiratory

mass which

effect

tract

infection.

extends

along

the

of the left hemidiaphnagm.

(C)

mass causes left diaphragmatic lobules. (d) Cut surface of the

at MR (Fig 9a and 9b reprinted,

with

(a)

PA chest

on the mediastinum.

permission,

Rosado-de-Christenson

entire

radiograph

(b) Lateral

chest

anteroposterior

Coronal

Ti-weighted

mag-

inversion. There is heterogeneous 30 x 19 x 1 1-cm thymoma shows

from

reference

et a!

15.)

U

RadioGrapbics

U

159

Figure

10.

Invasive

41.year-old

man.

lobulated volume

in an asymptomatic radiograph shows

PA chest

a

mass in the left superior mediastinum, loss of the left lung, and elevation of the he-

midiaphragm.

left upper through a lobulated

Increased

lung.

markings

superior

the

aspect

soft-tissue The

left lung

is irregular,

of the mass and

plants

found.

lung

aontic

mass

suggestive

with

arch

the

shows

mediadjacent

(c) Axial

inferior

infiltration

an invasive

invasion

the

of invasion.

through

apparent

At surgery,

pericardial was

of the

shows

in the

in the left anterior

CT scan

lung.

noted

axial CT scan

of the

mass

interface

contrast.enhanced adjacent

are

(b) Contrast-enhanced

astinum.

pect

thymoma

(a)

as-

of the

thymoma

and pleural

with

tumor

ima.

b.

C-

suggestive

of invasion

but

may

not

always

CT Appearance CT is the imaging the radiographic .

be

seen on plain nadiographs (1 1) (Fig 10). Rarely, invasive thymomas may manifest as predominant pleural disease. In these cases, nadiographs may show unilateral pleural thickening; pleural masses; or diffuse, nodulan, circumferential pleural thickening that encases the ipsilatenal lung. The latter presentation

may

mimic

the

radiographic

malignant metastatic

mesothelioma to the pleura.

or

When

thymomas

affect

and

invasive

surfaces, the (11,12,16).

involvement

num tients normal

the lung

on an abnormally

(17).

CT can reveal

with myasthenia radiographic

widened

small

gravis results.

mediasti-

tumors

in pa-

who have It is also useful

in

the evaluation of structures adjacent to the tumor in patients with suspected invasive thymoma (18). On CT scans, thymomas are generally seen

appear-

ance of diffuse adenocarcinoma pleural unilateral

nal mass

modality of choice following demonstration of a mediasti-

is usually

as homogeneous, soft-tissue masses the region of the thymus and closely to the root of the aorta and pulmonary

located in related artery.

The bonders

smooth

of the mass

are usually

but may be bosselated or lobulated. The mass may be partially on completely outlined by fat

160

U

RadioGraphics

U

Rosado-de-Christenson

et a!

Volume

12

Number

1

e 11. Encapsulated thymoma in a 64-year-old asymptomatic woman. An anterior mediastinal mass was found incidentally. Axial contrast-enhanced CT scan shows a rounded, homogeneous mass of soft-

ue attenuation iass

is outlined

here

is a tissue

cending

aorta.

Figure

a. Figure found

b. 12. Invasive thymoma in a 60-year-old incidentally. (a) Axial contrast-enhanced

with

a central

area

of fibrosis

area

of decreased

is seen

within

on may completely

replace

astinal fat (18) (Figs projects to one side may extend to both

(19,20).

On scans

administration enhances

and

of contrast homogeneously,

hemorrhage

With increasing fatty involution, thymoma easier

age. Younger

January

1992

and

the anterior

are present

after

the

unless

necrosis

polymyositis.

to the area

medi-

mic sue

usually but

mass

(20).

between

The fat, and

the mass and the asspecimen

An anterior shows shows

is illustrated

tissue that attenuation fat.

However,

was

tumor A central

seen

at CT.

as an area of soft-tisanterior mediastinum

nodules

as with

mass

lobulated mass.

attenuation

appears in the

Detection

mediastinal

an ovoid, a lobulated

of decreased

these individuals may Areas of decreased ing to cystic changes 14).

borders.

ofmediastinal

gross

or as soft-tissue astinal

rim

2.

corresponds

intravenous

material,

with

plane Resected

CT scan through the mass (b) Cut surface of the tumor

attenuation.

the tumor

1 1, 12). The mass of the mediastinum sides of the midline

obtained

woman

with well-defined by a thin

within ofsmall

anterior thymomas

be difficult

with

attenuation may be seen other

cystic

mediin

CT

(18).

correspond(Figs 13, masses

in

age, the thymus undergoes which makes the detection of in patients over 40 years of

patients

may have

residual

thy-

Rosado-de-Christenson

et a!

U

RadioGrapbics

U

161

C.

e.

Figure 13. radiographs

rounded,

anterior

of attenuation

the mass

shows

posterior

wall

surgery,

U

right

by tissue

suggestive

162

Encapsulated, showed a large

it

of the

offluid.

mass.

mass.

is less (c)

A nodule

Coronal cystic

shows (e)

U

than cystic

in a 46-year-old mediastinal mass.

A nodule

several

Close-up

solid

with vague

(a) Axial

of increased

complaints.

contrast-enhanced

attenuation

PA and

lateral

CT scan

is seen

anteriorly,

shows

chest a

surrounded

that

of skeletal muscle or vascular structures. (b) Sonogram through good through transmission. An additional nodule arises from T2-weighted MR image shows high signal intensity inside the mass, signal

thymoma

view

man

with

ofdecreased

encapsulated

residual

RadioGrapbics

mediastinal is partially

of the cyst content thymoma.

thymoma anterior

that

that

a large

cystic right

nodules of one

Rosado-de-Christenson

intensity

was

resected.

attached of the

tumor

et a!

is noted

on the

medial

wall

ofthe

cystic

mass.

the

At

(d) Cut surface of the thymoma after evacuation to the internal wall of the cyst. These represented nodules

shows

the

lobulated

borders.

Volume

12

Number

I

!_:s

_:‘.

L..

b

A

15b. Figures

14, 15. (14) Encapsulated, completely cystic thyrnoma in an asymptomatic 37-year-old man with a media.stinal mass found incidentally. (a) Axial contrastenhanced CT scan shows a round, left anterior mediastinal mass with attenuation less than that of skeletal muscle and a thin, linear, peripheral calcified rim posteromedially. The mass is entirely surrounded by mediastinal

fat.

(b)

Cut

surface

ofthe

2.5-cm

tumor

ex-

cised cystic

from the left lobe of the thymus shows a round, mass with a smooth but septated internal wall. (15) Invasive thymoma in a 30-year-old woman with myasthenia gravis. PA and lateral chest radiognaphs showed a subtle contour abnormality of the left supenor mediastinum. (a) Contrast-enhanced CT scan at

L

11

Li

15c.

.

.

the attenuatlon

values

the cyst fluid may approach those sue, depending on the composition fluid. Areas ofdecreased attenuation

in the thymus. (c) Parasagittal TI-weighted MR image shows low signal intensity within the anterior mediastinal fat, just anterior to the ascending aorta. At surgery, a 4 x 1 .2 x 1 .2-cm thymoma with focal microsity

scopic

.

the mediastinum,

the level of the aortic arch shows an area of soft-tissue attenuation in the anterior mediastinum with a small focus ofcentral calcification. The left lobe ofthe thymus has a rounded, convex contour. (b) Axial T2weighted MR image shows heterogeneous signal inten-

invasion

ofthe

capsule

was found.

of

of soft tisof the seen on

CT scans may also correspond to foci of hemorrhage and necrosis within the mass (2) (Figs 5c, 6c). Calcification, even ifsubtle, can be easily

January

detected

1992

with

CT

(Figs

6c,

6d,

1 5a).

Rosado-de-Christenson

et a!

U

RadioGraphics

U

163

16a.

16b.

17a.

17b.

Figures

16,

raphy

17.

revealed

with

rim

a right

thymoma

(17)

uation

replaces

of the at the invasive

scan

the

and

164

U

superior

chest

wall,

of the

heart

and

in an

mediastinal cava.

suggestive

replaced

dyspnea,

soft-tissue

nausea,

and

CT

shows

scan

attenuation

was

of the

Prominent

a portion woman

mass

vena

extension

of the

ofthe

with

found

vessel

caval

fat.

the

wall

(b)

right

border

penetrating heart

(a) Axial

the

failure

and

contrast-en-

of heterogeneous

are

Axial

atrium.

mass

medial

without

A mass

vessels

obstruction.

into

the

vein shows venous a 10.5 x 9.0 x 8.0-cm

radiography.

mediastinal

Radiog-

a rounded

ofcongestive

material-filled

mass

weakness.

beyond

a history

at chest

anterior

contrast

of superior

shows

with

contrast-enhanced

and

80-year-old

replacement vena

Axial

CT scan at the level of the left brachiocephalic invasion into the vascular lumen. At surgery, invaded

demonstrate

surrounding

into

mediastinal the

tumor

(Figs

16,

between

structures

does

U

fat

structures

of fat planes presence

infiltra-

mediastinal

vascular

thymoma

absence

RadioGrapbics

anterior

right

growth

ily denote

mediastinum

tumor

(a)

man

noted

atten-

in the

soft

tis-

contrast-enhanced

Biopsy

of the

CT

tumor

revealed

thymoma.

ofinvasive

the

anterior

soft-tissue

level

of the

tumor

mass.

thymoma

A right shows

CT may directly tion

in a 74-year-old

mediastinal

left

The

Invasive

edema. CT

an

in the

removed.

was

hanced

sues scan

thymoma

(b) Axial contrast-enhanced by the mass and apparent

lumen.

extremity

Invasive anterior

calcification

of the mass. encasement vessel

(16)

17).

of invasion

presence

and

in cases

and

ence

of invasion

However,

sensitive

the

tion

not

mass

in

necessar(20).

Rosado-de-Christenson

Ct a!

the than

borders

adjacent

the evaluation by the

lung

(Fig lob, chest

between

of the

of pleural tumor

the

suggests

lOc).

the in the

adjacent

and

pres-

CT is more

radiography

of involvement

seeding

The

of irregular

mass

detec-

lung

and

extrapleural

(1 1, 18, 19)

Volume

(Figs

18,

12

19).

Number

1

19b. Figures old man

18, 19.

anterior

media.stinal

phy. dow

mass.

with

(18)

nausea,

Invasive

dyspnea, mass

was

(a) Axial CT scan obtained settings shows a lobulated,

thymoma in a 35-yearand vomiting. A large found

at chest

radiogra-

with mediastinal winanterior media.stinal

(b) Axial CT scan of the lower

lung obtained

with lung window settings shows two nodules closely related to the diaphragmatic pleura. At surgery, visceral and panietal pleural invasion by tumor and multiple pleural tumor implants were found. (19) Thymoma in a 64-year-old man suspected of having diffuse malignant mesothelioma. (a) PA chest radiograph

19C.

January

shows

diffuse,

circumferential,

nodular

thicken-

ing of the right pleura, with encasement of the right lung. (b) Lateral chest radiograph shows diffuse plcural thickening. (c) Axial contrast-enhanced CT scan shows a lobulated soft-tissue mass adjacent to the right cardiac border. There is nodular thickening of the right pleura and involvement of the major fissure and the mediastinal pleura. Findings from pleural biopsy confirmed the diagnosis of thymoma.

1992

Rosado-de-Christenson

et a!

U

RadioGraphics

U

165

a.

b.

Figure woman

20. with

Invasive thymoma a 2 . 5-year history

in a 42-year-old

of superior vena caval syndrome. (a) Axial gated MR image (echo time = 28 msec) through the left atrium shows left-sided, lobulated anterior mediastinal mass ducing mass effect on the mediastinum. There increased signal intensity within the lumen of superior vena cava and right atrium. (b) Coronal gated MR image (echo time = 28 msec) shows

left anterior nal intensity tending obtained growing invaded

a prois the the

mediastinal mass and the abnormal sigfilling the superior vena cava and ex-

into the right atrium. (c) Gross specimen at autopsy shows the invasive thymoma into the right atrium. The left-sided mass the left lung and was contiguous with tu-

mor

and

thrombus

and

right

atrium.

found

in the superior

vena

cava C.

MR Imaging Appearance MR imaging is useful in the detection

.

ance

and

characterization of mediastinal masses and their relationship to adjacent structures. Thymomas are described as masses that are isointense relative to skeletal muscle on Tlweighted images and that increase in signal intensity (approaching that of fat) on T2weighted images (21,22) (Fig 15b, 15c). Cysts with high water content in thymomas may be

Multiplanan structures

structures,

166

U

RadioGrapbics

(Fig

Because

l5c). flow

within

of its

vascular

is an excellent

evaluating

nonin-

possible

by thymoma

without

contrast

material

vascular

the

need

(22,23)

(Fig

20). U

THERAPY

Complete

surgical

excision

can be accom-

pushed in virtually all completely lated (stage I) thymomas (24). procedure may involve removal

with MR may be useful and surrounding in which the CT appear-

Rosado-de-Christenson

for

for intravenous

imaging

U

MR imaging method

involvement

itself

on complete

excision

encapsuThe surgical of the tumor

of the

tumor

and

adjacent uninvolved thymus gland. Extended thymectomy-the en bloc removal of the thymus and the surrounding adipose tissueshas also been used in the treatment of myasthenia gravis, with on without associated thymoma (25).

thymomas

in cases

(23)

to demonstrate

vasive

detected as areas of low signal intensity on Ti-weighted images and high signal intensity on T2-weighted images (22) (Fig 13c, 13d). in evaluating

is equivocal

capability

Ct a!

Volume

12

Number

1

excision of the tumor, if feasible, is treatment for patients with inva-

Radical

the preferred

sive thymoma. resection has

Complete, also been

aggressive, advocated

surgical for treat-

as an

tumor

recurrence

generally

advocated

excision

for treatment of Radiation therapy

as an adjunct

for cases

of invasive

ularly when only subtotal formed. Others recommend tion

for

all thymomas,

is

to surgical

thymoma,

partic-

completely encapsulated these tumors may recur

stage

thymomas, and rarely

I on

because metastasize

The

role

of chemotherapy is less

clear.

for treatment

Combination

long-term

benefits

of

are

still

unknown (28,29). In addition, glucocorticoids have been used in the treatment of invaor

metastatic

myasthenia be effective have

thymoma

gravis.

This

when

other

failed

associated latter

approach

PROGNOSIS The prognosis of patients with thymoma is related to the stage of the tumor. Stage I thymomas have the best prognosis. Five-year sunvivals of92.6% have been reported in patients following

surgical excision (14). Nonetheless, are rare reported cases oflocal tumor recurrence and distant metastatic spread in these patients (24). Invasive thymomas carry a worse prognosis. with

tumors

with

microscopic

capsu-

Patients

tumors

have

with

5-year

respectively

stage

survival (14).

The

U

1.

patients,

who

adjuvant

radiation

been shown to be an effective control of disease (31).

1992

have

or biopsy have 45%, respectively

symptoms

of

neoplasms

of local

may

be

are

associated

compression

Because

of

thymomas on with

of their

potential

these tumors should surgical excision. An

of these

lesions

and

the

timely

treat-

of the patients.

stage

We thank

REFERENCES Davis RDJr, num:

2.

3.

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4.

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survival

undergone

Oldham

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E. Kinsey,

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Sabiston

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Airan B, Sharma R, Iyer KS, et al. Malignant thymoma presenting as intracardiac tumor and superior vena caval obstruction. Ann Thorac Surg 1990; 50:989-99 1. Rosenow EC III, Hunley BT. Disorders of the thymus: 763-770.

Bailey

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Dana

S. Baker for their in the preparation

methods of diagnosis, management, and resuits. Ann Thorac Sung 1987; 44:229-237. Marchevsky AM, Kaneko M. Tumors of the thymus: thymomas. In: Marchevsky AM, Kaneko M, eds. Surgical pathology of the mediastinum. New York: Raven, 1984; 58-116. Furman WL, Buckley PJ, Green AA, Stokes DC,

5-year sun(24). In

means

they

disorders.

Primary

6.

thymoma

the

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Most

Clarice Williams, and Wendy search and clerical assistance this manuscript.

with

invasive

but

ofthe

of 69.6%

overall

thymic

primary

mediastinum.

diagnosis

5.

subtotal resection vivals of 59% and

January

III and

rates

is not

understanding of the clinical features, monphologic characteristics, and various radiologic appearances is helpful in the early

rate for patients with invasive thymoma approaches that for patients with noninvasive tumors if radical excision is possible. Patients

these

anterior

epithelial

common

Chien LT. Thymoma in a 4-year-old child:

or macroscopic invasion of the mediastinal fat and the adjacent mediastinal pleura (stage II lesions) have 5-year survivals of85.7%.

more

this

of nonmyasthenic

for aggressive behavior, be treated with complete

lar invasion

50%,

the most

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com-

plete there

Patients

that

Acknowledgments:

U

thymoma

that

may

thena-

(30).

encapsulated

prognosis,

suggests

gravis regarded

however, patients may die of myasthenia gravis (14).

SUMMARY Thymomas are

ment

with

conventional

been

U

systemic

chemo-

of chemotherapy

had

of a poon

than

(34);

complications

the

therapy has been effective in treating patients who have undergone subtotal resection or who have recurrent or metastatic tumor. The

with

is lower

asymptomatic,

thymoma

pies

moma

and

(26,27).

sive

evidence

thymoma

excision is peradjuvant irnadia-

including

of myasthenia

thymoma

case. There have been reports of a better prognosis for patients with myasthenia gravis and thymoma (32,33); prognosis may be improved because the tumors in patients with myasthenia gravis are diagnosed earlier, at a time when they are still resectable. In addition, the recurrence rate of myasthenic thy-

(14).

Use of radiation therapy thymoma is controversial.

the presence with

indication

recent

ment of recurrent thymoma in the mediastinum or pleura. Patients with myasthenia gravis who undergo resection of recurrent thymoma may experience improvement of myasthenic symptoms that were associated with

Although in patients

red blood

gravis

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Intern

HG, Rubin with

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Education 199

K, lioka

clinicopathological Ann

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Thorac

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Recur-

fea-

106),

published

are given

below.

7.c

Volume

12

Number

1

Thymoma: radiologic-pathologic correlation.

Thymoma is the most common primary neoplasm of the thymus. The majority of thymomas are encapsulated masses and exhibit a benign behavior. Less freque...
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