Karl

Wernecke,

MD

Thymic CT and

#{149} Pierre

Vassallo,

Involvement Sonographic

To evaluate the morphologic characteristics and frequency of thymic en-

largement in Hodgkin disease, the initial and follow-up computed tomographic (CT) scans of 43 patients with newly diagnosed Hodgkin lymphoma were retrospectively analyzed. Sonograms of the thymic region in 21 patients were also available the CT

and scans.

showed

were Initial

thymic

with

compared CT scans

enlargement

in 17 of

the 43 patients, no evidence of thymic enlargement in 15 patients, and equivocal findings in 11 patients.

Analysis of follow-up CT scans mdicated that seven of the 11 patients with initially equivocal findings had had

thymic

enlargement.

patients, mor

the anterior

with

shrank

adopted mic

In all

thymic

of the

CT scans showed that sonography could not help differentiate the northymus tissue. All

fatty

from thymic

in Hodgkin Findings’

T

involvement

HYMIC

surrounding glands that

were considered diseased because of enlargement at CT were sonographically visible due to an abnormal, hypoechoic structure. The results of the study show that thymic enlargement presumed to be due to involvement

is a well-rec-

months

were

available

Since

September

vanced

the study both preparasternal

with

bulky

mediastinal

lesions, the differentiation between thymic and/or lymph node tumors is extremely difficult. Whether followup CT scans obtained after therapy can help to elucidate the identity of such mediastinal tumors is as yet unclear.

additional

information

mdi-

cating thymic enlargement was present. An attempt was also made to establish sonographic criteria to identify thymic glands that were considered diseased because they were enlarged at CT and to assess the diagnostic value of combined mediastinal CT and

sonography

for

this

purpose.

Patient

AND

of 104 consecutive diagnosed Hodgkin

ported.

available

were

67.3421

#{149} Me-

CT, 67.1211 #{149} Mediastinum, neo#{149} Mediastinum, US studies, 67.1298 #{149} Thymus, CT, 676.1211 #{149} Thymus, neoplasms, 676.342 diastinum, plasms,

67.342

Radiology

1991;

181:375-383

newly

treated

live

cluded

at our

study.

The

because

hospital

between

selected other

for

this

61 patients

CT scans

before

disease

developed

only

had

(n

Hodgkin

disease

within

0.5-36

months).

parasternal technique

the

latter

was

half

follow-up

and after

therapy

25 women

and

were

65)

=

of

21 patients had CT scans and Eighteen of the 21

undergone

during

There

of

of therapy

all patients

with this

period, only and posttherapy sonograms.

raphy

sonog-

(range, 18 men

in

our study; ages ranged from 17 to 65 years (mean, 33.4 years). Hodgkin disease was diagnosed by means of peripheral lymph node biopsy (n = 35), isolated mediastinal

lymphomas (n = 4), and

through mediastinoscopy percutaneous biopsy

Twenty-seven

patients

Hodgkin

disease,

had

eight

(n

stage

4).

=

II

had stage

III dis-

ease, six had stage IV disease, and two had stage I disease. Eighteen patients were treated with radiation therapy alone, two with

chemotherapy

combined

CT

alone,

and

23 with

obtained

with

a Tomo-

(Philips,

Shelton,

therapy.

Examination scans

Technique were

scan 350 imager

been

January

bolus

administration

material

previously

Image

retrospecwere

1986,

diagnosed examined Because

patients

a period

in 25 of our 43 patients.

Conn)

of 100-200

(Ultravist

Mediastinal sonograms with 3.5- and 5.0-MHz 7000; Picker International, technique of mediastinal

patients

January 1989 were reviewed. patients in whom CT scans before and after therapy were

disease,

newly

over

completion

mL

300; Scher-

ing-AG, Berlin) in a rapid sequence (scan time, 4.8 sec; section thickness, 0.9 cm).

METHODS

Selection

The records

after

have been sonography.

after

1984 and Forty-three obtained

Hodgkin

with

of contrast

MATERIALS

MD

obtained

3-30

cases

Potter,

examinations)

with

terms:

#{149} Richard

ognized feature of Hodgkin disease; however, its exact prevalence is unknown (1-3). To date, studies evaluating computed tomographic (CT) criteria of thymic involvement in Hodgkin disease are few (4-7). In ad-

by Hodgkin disease seems to occur more frequently than previously re-

Index

MD

Disease:

whether

enlargement,

the thymus remained enlarged after therapy and full clinical remission. The comparison of sonograms and

mal-size

E. Peters,

24

tu-

and

In nine

with

#{149} Peter

thy-

seven

tongue-shaped

configuration.

Rutsch

In this study, we have analyzed thoracic CT scans obtained in 43 patients with newly diagnosed Hodgkin disease to evaluate the frequency of thymic enlargement at initial examination. The follow-up CT examinations were then evaluated to assess

mediastinal

therapy

a typical

patients

#{149} Frank

MD

ex-

therapy

were obtained at other institutions and were not available for retrospective evaluation. Follow-up CT scans (one to three

were obtained transducers (LSC Munich). The sonography has

described

(8,9).

Analysis

CT-Retrospective analysis CT scans included assessment ration, size, and internal texture

of the initial of configu-

thymus

lymph

and adjacent

nodes. The thymus mal if one or more

enlarged

of the

was considered of the following

abnorwas

found: (a) a triangular or bibbed thymus that was markedly enlarged (thickness of I From the Institute of Clinical Radiology, University of Muenster, D-4400 Muenster, Germany. Received December 6, 1990; revision sion received March 13; accepted May 16. Address reprint requests ©

RSNA,

1991

Albert-Schweitzer-Str requested February to K.W.

33, 5, 1991; reviAbbreviation:

SD = standard

deviation.

375

left thymic lobe over 2 standard deviations [SDs] greater than the normal age-related range) (4,7), (b) an obvious convex displacement

of the

visceral

the presence

(c)

diastinal

pleura

of cysts

tumor

(3,11)

(Fig

Anterior mediastinal globular configuration cysts

were

(6,10),

or

in an anterior

me-

Ia).

masses with a and no evidence

classified

as equivocal

of

lesions

because a definite differentiation from lymph node tumors was not possible with morphologic criteria alone. If follow-up CT showed a regression in size with the

adoption of a typical triangular shape in a previously equivocal anterior mediastinal mass, the mass was then reclassified as an

abnormal thymus (Fig I). In thymic glands with a globular uration, response accordance Francis

than

with et al (6),

criteria a sagittal

2 SDs from

range

was

suggested diameter

the normal

considered

assessed

findings.

age-related

knowledge

experience

have performed in more than

mediastinal 2,000 adults),

adult

cannot

thymus

b.

findings

without

In our

a.

by more

abnormal.

Sonography.-Sonographic

were

config-

changes in the sagittal diameter in to therapy were monitored. In

of CT

(to date,

we

sonography the normal

be delineated

from

surrounding tissue at sonography because of an inadequate difference in echogenicity.

If connective

and

anterior

mediastinum

neously normal.

hyperechoic, Any lesion

eated

from

fatty

tissue

were

that

of the

homoge-

this was recorded could be delin-

surrounding

tissue

of the

as ante-

nor mediastinum was recorded as abnormal and its configuration, size, and echo texture were assessed. Anterior

mediastinal

lesions

detected

(which

is best

nal sagittal there were id).

demonstrated

on

paraster-

sonograms [Fig Ic, ld]) or if cysts within the lesion (Fig ic,

All raphy

nodular lesions that showed

were

considered

detected no evidence

equivocal,

differentiation

between

and lymph

node

on the basis

with sonogof cysts

since

a reliable

enlarged

tumors

thymus

figuration

on follow-up

reclassified Finally, compared

as thymic tumors. the sonographic findings were with CT findings to establish

glands CT

that

were

sonograms

to identify considered

were

thymic diseased

with

CT Findings Therapy

before

evidence

and

376

of thymic

1; Table

#{149} Radiology

regression

therapy

extensive

of an enlarged

in a 25-year-old

globular

tumor

in the

patient anterior

thymic

gland

at CT and

sonography

before

with

Hodgkin

disease.

(a) Initial

CT scan

mediastinum

(sagittal

diameter,

5 cm),

unequivocally identified as the thymus. Only the presence of small cysts suggests that the tumor might be of thymic origin. (b) CT scan obtained after reduction in tumor size and the adoption of a typical thymic configuration left

thymic lobe, 1.2 cm). (c) Initial sonogram (left parasternal sagittal tumor (arrowheads) with a roughly triangular shape and a central (z) lying anterior to the right pulmonary artery (p). (d) Sonogram obtained after therapy shows that the tumor has regressed to an echogenic prevascular lesion (TH, arrowheads) a typical thymic tongue-shaped configuration. P = right pulmonary artery.

the CT findings were equivocal in regard to the nature of the anterior mediastinal tumor (Fig 2; Table 1). Follow-up CT enlargement

seven

scans had

of the

showed that been present

11 patients

findings.

who

In all seven

(sagittal

view) cyst

with

after

enlargement

1). In 11 patients,

after

thymic in

had pa-

therapy

(Fig

2, Table

four with

patients (Table a prevascular

measuring shrinkage

residual prevascular this patient.

1).

In spite of further follow-up with CT, the nature of prevascular lesions detected with CT remained unclear 1). In one

patient

nodular lesion 3.0 cm in sagittal diameter, was observed after therapy

diameter,

1.8 cm)

but

the

nodular configuration persisted (Fig 3). According to Francis et al (6), residual thymic tissue, particularly in patients older than age 50 years, may have a globular configuration. Thus, we were unable to differentiate between residual thymic tissue and a

tients, a previously nodular mass showed clear shrinkage and the adoption of a typical triangular shape

CT scans obtained before therapy showed no evidence of thymic enlargement in 15 of the 43 patients and in 17 (Fig

an

which cannot be within the lesion therapy shows a (thickness of the shows a hypoechoic

equivocal

criteria.

RESULTS

clear

shows

show

characteristics

alone. Initially, globular anterior mediastinal lesions that had a tongue-shaped con-

criteria

Figure 1. Images and after radiation

was not possible

of sonographic

sonographic

d.

C.

with sonography were considered to represent thymic tissue if they had a typical thymic tongue-shaped configuration

in

lymph

node

in

In two patients with multiple enlarged anterior mediastinal nodes, complete regression was observed in one patient after therapy; a multinodular lesion persisted in the second patient (Fig 4). The differential diagnosis proposed in both these cases was of nodular involvement of the November

1991

Table

1

CT Findings

at Initial

and Follow-up

Examination

in 43 Patients

with

Hodgkin

Disease

Findings Examination

No Thymic

Initial

Thymus

Enlargement

of normal

size

Equivocal

(n = 12)

Large

Thymic

prevascular

tissue

(n = 3)

Follow-up

Thymic

size unchanged

Regression

=

Complete

disappearance

of the thymus

4)

(n

No thymic

tissue

identified

(n

Enlarged

8)

=

(n = 3)

Initially multiple cm in diameter) sion (n = 1)

prevascular

Initially

prevascular

show

multiple

cm in diameter)

nodules

complete

show

displacement

(2.0

nodules

(2.0

to mul-

dence

residual nodules of 1.0 cm in diameter (n = 1) Thymus of marginal size shows regression to normal size (n = 1) Patients

with

equivocal

thymic

involvement

thymus by Hodgkin disease or multiple enlarged prevascular lymph nodes, with complete regression in the first case and residual lesions in the second. In

one

patient

with

a thymic

size

CT enabled us to diagnose enlargement in 24 (56%) of 43

short,

thymic patients

and

ment

in

15

exclude

CT findings

Thymic

Internal

enlarge-

In four (9%) pawere equivocal.

(35%).

tients,

thymic

Size

In

six

(25%)

of

24

mic enlargement, tially homogeneous.

patients

the

the 24 patients, the had an inhomogeneous nal structure at CT

with

thy-

available

in

enlarged

12

patients

tial thymic enlargement; the showed no evidence of new mation within the thymus.

Volume

181

#{149} Number

2

with

mi-

scans cyst for-

Sonographic after Therapy

enlarged lobe over

Patients

2

and

tently There

thymic the

size

size,

enlarged

both

glands,

of a persis-

after therapy. in decrease

of normal

relating

ences in type of therapy therapy alone, n = 18; apy and chemotherapy,

and

and

to differ-

n

=

involvement

23).

the

histologic

in all 24 patients are shown

than

years, Only years

with in Ta-

without enlargement years ± 16.9) (x2 test; P < .05). patients between 17 and 40 72.4% had thymic enlargement. 35.7% of patients more than 40 of age showed thymic enlarge-

ment. quency

men ever,

those

Women

showed

of thymic

(women, the

according

significant.

enlargement

64%;

differences to

a higher

sex

men, in

were

frethan

44%).

How-

distribution

not

tients,

initial

statistically

had In

tongue-shaped

multiple, the anterior with

nodules

the prevascular origin in only

within lar

mass.

n

The

an

mass

patients

1, 3). In the sonography

hypoechoic mediastinum.

CT scans were

nodules

indicated

located

thymus (Fig 7). indicated that

of thymic

enlargement

thymic tongue-shaped and cysts, n = 2; cysts

an anterior

mass,

pa-

lesion was of thymic four of the 15 patients

evidence

at CT (typical configuration

15

showed in two

within an enlarged Initial sonography

with

follow-up

all

sonography

mediastinal

these

at

of thymic at CT. Twelve

and nodular in 10 (Figs three remaining patients,

that

and

enlargement

also

available.

Comparison

lymph

ble 3. A statistically significant difference in age was observed between patients with and without thymic enlargement. Patients with thymic enlargement were younger (29.6 years ± (38.6

shows

before

evidence was seen

15 patients

showed within

Data

and

subclassification thymic enlargement

Among

2)

obtained before available in 15 patients

clear

sonograms

was

ther-

of concurrent

of the

anterior

(radiation

radiation

Pathologic

frequency

before

frequency

enlarged thymus was no difference

in thymic

8.6)

=

displacement

with thymic

in whom enlargement

between

therapy

node

(n

Findings

lation

The

thymus nodular inter(Fig 2). In five (21%) patients, CT showed cysts measuring 1.0-3.0 cm in diameter within the enlarged thymus (one patient had one cyst, two had two cysts, and two had multiple small cysts) (Fig 1). In all five patients, the cysts showed a reduction in size with therapy and completely disappeared at completion of therapy (Fig 1). Follow-up CT scans obtained 3-30 months after therapy were

Therapy

CT.-Sonograms therapy were

at CT

thymus was miIn 13 (54%) of

of pleural

SDs) in nine of 24 patients after therapy (Figs 2, 6). Table 2 shows a corre-

Clinical Texture

during

The thymus remained (thickness of left thymic at

of the pleura

examination.

Thymic

the upper limit of the normal range, shrinkage was observed after therapy, and we could not differentiate between a regressing thymic lymphoma and normal thymic involution (Fig 5). In

CT

at initial

lobe,

regression (n = 2) Initially globular tumor shows regression in size with the adoption of a typical triangular shape (n = 7*)

tiple

*

ofleft

triangular(a = 10)

Initially enlarged thymus shows shrinkage to normal size and typical triangularshaped configuration (n = 10) Initially globular tumor with cysts shows shrinkage and adoption of typical thymic triangular shape. Cysts disappeared completely (n = 5) Thymus of initially marginal size with evi-

regres-

shrinkage

(thickness

cm) with typical

shaped configuration Large prevascular globular tumor (4.5-12.0 cm in sagittal diameter) with cysts (n = 5) Thymic size at the upper limit, but convex

of multiple nodules meacm in diameter (ii = 2)

0.5-2.0

Enlargement

thymus

2.0-3.5

Thymic size at the upper limit of the normal range (n = 1) Initially globular tumor (3.0 cm in diameter) shows shrinkage to a residual nodule of 1.8 cm in diameter (n = 1)

(n = 2) size (n = 6)

of thymic

measur-

cm in diameter

Conglomeration

suring

Thymic

globularlesion

ing 3.0-11.0 No thymic

Involvement

=

mediastinal

globu-

2).

In the 12 patients low-up sonograms

in whom folwere available,

clear shrinkage of all prevascular masses was evident after therapy (Figs 1, 3). In all eight patients with globular anterior mediastinal mass

a

a on

initial sonograms, a further shrinkage in lesion size was observed after completion of therapy, along with the adoption of a typical tongue-shaped configuration

best

demonstrated Radiology

with

#{149} 377

the

parasternal

3). The

sagittal

prevascular

therefore,

view

(Figs

masses

1,

could,

be retrospectively

classified

as thymic tumors in all these cases. One anterior mediastinal mass with typical tongue-shaped thymic config-

uration

at initial

a

showed three with multiple, hypoechoic nodules, shrinkage to a single residual tongue-shaped mass was observed in one patient, and shrinkage to multiple small nodular lesions was observed in two patients. It is worth noting that an abnormal shrinkage patients

echogenicity

long

sonography

after

of the

after

In the

therapy.

thymus

full clinical

persisted

remission

(up

to

a.

b.

months after therapy) in all 12 patients with follow-up sonograms and thymic enlargement at CT. This obser17

vation was true for patients with residual thymic enlargement at CT after therapy, as well as for patients whose thymus

had

size.

Thus,

eated

from

long the

to its normal

thymus

clinical

1, 2). In eight increased follow-up

the

of the

12 patients,

thymus

during period.

the

remained

sonoIn four

structure

pa-

of the

unchanged.

In five patients, initial sonographic after

tissue

occurred

of the

hypoechoic

appeared

be delin-

fatty

remission

echogenicity

slowly graphic tients, thymus

could

surrounding

after

(Figs

returned

the

thymic cysts examinations therapy.

seen at dis-

In only

one

patient, showed

follow-up sonography the development of a thymic

cyst

cm

(0.8

detected Patients

In the

in diameter)

with with

that

was

not

CT. normal

thymus

at CT.-

three

patients with a normal at initial CT, sonography not enable delineation of the from surrounding fatty tissue.

thymus

could gland

Patients with equivocal ment at CT-Follow-up

thymic

nodular

diameter

sisted unchanged 3). In another

CT findings, tiple nodules

for patient

of 1.8

maintained this lesion

configuration;

its per-

ules 378

persistence (Fig

a conglomeration (resembling

of multiple

4). In one

#{149} Radiology

the CT findings. larged residual

of mula bunch of

patient

small with

Because of its triangular thymic gland. TP = main

mic

size

at the

noda thy-

upper

at CT, sonograms hypoechoic ules, which, scans, were

within

the

gressed preaortic

limit

configuration, pulmonary

of normal

showed

multiple

anterior mediastinal nodwhen compared with CT determined to be located

thymus.

These

with therapy; node persisted

12 months (Fig with equivocal

grapes) was seen in the anterior mediastinum at CT and sonography (Fig 4). At completion of therapy, the antenor mediastinum was sonographically normal, whereas CT indicated

the

2. CT scans and sonograms in a 22-year-old patient with a prevascular tumor of unclear origin (thymus or lymph node) at initial CT. (a) Initial CT scan shows a large tumor (sagittal diameter, 6 cm) with an inhomogeneous nodular internal structure in the anterior mediastinum. A differentiation between lymph node tumor and an enlarged thymus was not possible from this image. (b) CT scan obtained after therapy shows the triangular-shaped configuration of the lesion, indicating that the lesion was the thymus. The thymic size (thickness of the left lobe, 2.5 cm) is above the limits of the normal age-related range. The lesion also shows a persistent nodular internal structure. (c) Initial sonogram (left parasternal transverse section) shows a prevascular echogenic tumor (T, arrowheads) with a nodular internal structure. TP = main pulmonary artery, A = ascending aorta. (d) Follow-up sonogram obtained after therapy shows an echogenic residual tumor (T, arrowheads), which correlates well with Figure

the lesion was identified A = ascending aorta.

as an en-

artery,

enlarge-

sonograms were available in three of the four patients with equivocal thymic enlargement at CT. In one patient with an equivocal nodular anterior mediastinal lesion at CT, sonography also demonstrated an identical lesion of hypoechoic structure, which shrank to a maximal sagittal cm after therapy but

d.

C.

only

lesions

re-

a single, (Fig 5).

DISCUSSION

The that

results the

of this

frequency

study of thymic

suggest enlarge-

ment in Hodgkin disease (56%)-either isolated (14%) or combined with mediastinal (42%)-seems

reported (7). The enlargement

lymph node involvement to be greater than that

in previous CT studies (30%) higher frequency of thymic in our

series

could

prob-

ably be attributed to the availability of follow-up CT scans in all patients. The thymic origin of an anterior mediastinal mass in Hodgkin disease can frequently be diagnosed only with follow-up CT scans. Analysis of CT scans obtained before therapy showed clear morphologic indications of enlarged thymus in only 17 of the 43 patients with Hodgkin disease. The two morphologic criteria suggesting the presence of an enlarged thymus were a triangular-shaped configuration of the mass or the presence of cysts (Fig

1). CT findings

in regard

to thymic

enlargement were initially equivocal in 11 patients. In most of these cases, problems were encounted in classifying large globular lesions as an enlarged thymus or a lymph node tuNovember

1991

for our patients was the availability of CT scans obtained before and after therapy. Sixty-one of 104 consecutive patients seen during the study period were excluded because initial CT scans

obtained

at other

institutions

were not available for retrospective analysis. Our study population included patients with (79%) and without (21 %) mediastinal manifestation of Hodgkin disease. This constitutes a representative

with ease. cluded

only

thoracic scans; with

a.

sample

patients

no

Hodgkin diset al (7) inwith

Hodgkin

disease

evidence

of

on initial

CT

16 of 66 consecutive evidence of thoracic

and a thymus were excluded. been included,

b.

of patients

newly diagnosed In contrast, Heron

frequency

patients disease

of normal size at CT in If these patients had as in our study, the

of thymic

enlargement

would have been even lower (23%) than we observed. An important factor that could induce an overestimation of thymic involvement is the frequency of advanced stages of disease. Although in at least half of the patients Hodgkin disease localized to the mediastinum appears to originate in mediastinal lymph nodes, involvement of the thymus will secondarily occur when the disease advances (3). Twenty-nine (67%)

of our

patients

had

stage

I or II

disease and 14 (33%) had stage III or IV disease. Unfortunately, data about the stages of disease in the study by Heron et al (7) are not available; thus, it is not possible to compare the distribution of early and advanced cases in both d.

C.

Figure

3. CT scans and sonograms in a 49-year-old patient with a prevascular lesion of unclear origin. (a) Initial CT scan shows a globular prevascular tumor (sagittal diameter, 3.0 cm). (b) After therapy, CT scan shows a globular residual lesion (sagittal diameter, 1.8 cm), which remained unchanged on follow-up CT scans obtained 1 year later. (c) Initial sonogram (right parasternal sagittal view) shows a globular hypoechoic tumor (LK) anterior to the ascending aorta (AA). (d) Sonogram obtained after therapy, 1 year later, shows an oval hypoechoic residual lesion (L, arrowheads). With the sonographic criteria mentioned in the Discussion (persistence of hypoechoic structure), this lesion may be classified as residual thymic tissue. AA = ascending

mor

ocal

1, 2, 5). Follow-up thymic

of the

CT scans

enlargement

11 patients findings.

with

in seven

initially

In all seven

patients,

equivthe

anterior mediastinal tumor showed reduction in size and adopted a typical triangular thymic configuration after therapy (Figs 1, 2, 5; Table 1). The anterior mediastinal lesions in four patients could not be classified with morphologic criteria, even on further follow-up CT scans. In the study by Heron et al (7), only Volume

181

study

by

Keller

who examined of mediastinal obtained mic

#{149} Number

2

10 of 50 patients with newly diagnosed Hodgkin disease had both preand posttherapy CT scans available. If a larger number of these patients had undergone follow-up CT, more cases of thymic enlargement might have been identified. Other factors that could account for differences in the number of patients with thymic enlargement might be patient selection criteria and the proportion of patients with advanced disease.

The

only

selection

criterion

and

involvement

and

Castleman

histologic Hodgkin

at the

sis. Keller tients. They the increasing

aorta.

(Figs

showed

studies.

The higher frequency of thymic enlargement in our patient sample supported by the histopathologic

time

(3),

specimens lymphoma

of initial

Castleman

diagno-

found

in 21 (48%)

concluded

is

that,

thy-

of 44 pa-

due

to

fibrous reactions around lymphomatous infiltrates in at least half of the cases, Hodgkin disease located in the mediastinum appears to arise in the thymus. Keller and Castleman (3) have mdicated that cyst formation is a frequent and typical morphologic finding in lymphomatous involvement of the thymus. However, the presence of

cysts

in lymphomatous-involved

thy-

mic glands has rarely been described with previous cross-sectional imaging techniques (5,7). In our series, thymic cysts were found in five (21%) of 24 patients with an enlarged thymus.

Radiology

#{149} 379

Figure 4. CT scans and sonograms in a 23year-old patient with prevascular lesions of unclear origin (multiple lymph nodes or multifocal thymic involvement). scan shows a multinodular cm in diameter) prevascular scan obtained after therapy

tence

of multiple

(a) Initial CT (nodules up to 2.0 mass. (b) CT shows a persis-

nodular

prevascular

lesions

(up

to 1.0 cm in diameter). (c) Initial sonogram (right parasternal sagittal view) shows one of the several nodes (L) anterior to the ascending aorta (AA). (d) After therapy, this lesion and other lesions seen at CT are no longer evident on the sonogram. These sonographic and CT findings suggest that the lesions

seen

CT probably

at

residual

lymph

multinodular nary

nodes

represent

rather

residual P = right pulmo-

thymic tissue. LA = left atrium.

artery,

multiple

than

a. Moreover,

cysts,

our

when

results

morphologic

at the

that

are a reliable

indicator

of thymic tumor; ular prevascular correctly classified

glands

indicate

present,

b.

of the

presence

all five initially lesions, which as enlarged

initial

globwere thymic

examination

be-

cause of the presence of cysts, adopted a typical triangular thymic configuration after therapy (Table 1). The higher detection rate of thymic

cysts

in our

series

compared

with

those of previous studies might have several explanations. First, all of our patients received intravenous contrast medium. Contrast material enhancement of thymic tissue may assist in the identification of cysts. Second, the interpretation of a hypoattenuating area within a mass as a cyst or tumor necrosis is exceedingly difficult with morphologic criteria alone, particularly in the interpretation of small le-

sions.

Because

findings tleman of low

masses rather

of the

most than

likely

represented

necrosis.

This

is supported ings, which patients with our experience,

sistency

histopathologic

described by Keller and Cas(3), we assumed that the areas attenuation within prevascular

cysts

assumption

with sonographic findwere available in all five cystic the

of cystic

changes margin

lesions

at CT. In and con-

can

often

be

demonstrated more precisely with sonography than with CT-especially with use of 5.0-MHz transducers. Tumor necrosis often displays irregular margins and low-level internal echoes due to particulate necrotic debris. In contrast, the margins of cysts are generally sharper and internal echoes are fewer (Figs ic, 6b). However, the cystic nature of the lesions noted with CT and sonography has not been histologically proved in our study. Isolated thymic enlargement presumed to be Hodgkin disease was found in six (14%) of our 43 patients. 380

#{149} Radiology

d.

C.

Heron lated

et al (7) found thymic enlargement

tients

with

disease.

ancy

newly

In our

may

no

case of isoin 66 pa-

diagnosed opinion,

be due

Hodgkin

this

discrep-

to misinterpretation

of isolated thymic enlargement as antenor mediastinal lymph node involvement on initial CT scans. If a larger number of patients in the study by Heron et al had had both pre- and posttherapy scans, more cases of isolated thymic enlargement may have been identified as the thymus shrank and became triangular. The higher frequency of isolated thymic enlargement in our patients is again supported by the study of Keller and Castleman (3), who found isolated thymic involvement in 10 (23%) of 44 patients with newly diagnosed Hodgkin disHodgkin benign

ease. We ment

may with

postulated that thymic seen in 24 patients on

have been due to infiltration Hodgkin disease. Although

tologic

only

enlargeCT scans

confirmation

two

supported treatment mediastinal retically largement

of these

was

patients,

this

served in the spleen. logic study of Keller (3) does not support

his-

available

in

view

by the parallel response to with concurrently involved lymph nodes. It is theopossible that the thymic enobserved in patients with

lymphoma hyperplasia

is

To our knowledge, that show a purely

tic thymic pathologic

enlargement verification

is the result of as is often ob-

The histopathoand Castleman this hypothesis. no studies exist benign hyperplas-

with

histo-

at diagnosis

(3).

mic

Benign thymic enlargement rebound hyperplasia)

may

November

(thybe 1991

a.

b.

Figure lymph

5. Equivocal node (diameter,

being

at the upper

limit

of normal

size. (c) Initial sonogram mic region. Comparison

vena

cava

superior.

d.

C.

thymic involvement in a 28-year-old patient with Hodgkin 1.5 cm) and a marginally large thymic gland (thickness

range.

(right parasternal with CT scans

(d) Follow-up

of a single preaortic residual node ously described probably represented

a.

(b) Follow-up

CT scan obtained

transverse showed these

section) nodules

lymphomatous

after

radiation

6.

vascular

CT scans globular

(approximately

and

sonograms

mass

(sagittal

35 HU),

these

therapy

shows

involvement

diameter,

10 cm)

hypoattenuated

patient with

areas

with

several

could

a globular

small

a considerable

(arrows) enlarged

regression

prevascular

hypoattenuated

not unequivocally

as

in thymic

up to 1.0 cm in diameter thymus. AA = ascending

in the aorta,

thy-

C

=

with the persistence that the lesions previcava superior.

d.

C.

in a 22-year-old

shows an enlarged paratracheal size of the latter was classified

obvious regression of the prevascular nodules sonographic findings suggest, retrospectively, of the thymus. AA = ascending aorta, C = vena

b.

Figure

(a) Initial CT scan lobe, 1.1 cm). The

shows multiple hypoechoic nodules to be located within the marginally

sonogram obtained after therapy shows (L, arrowheads). The combined CT and focal

disease. of the left

mass zones

be identified

(up

at initial

CT. (a) Initial

CT scan

in diameter).

Because

of CT

(b) Corresponding

initial

sonogram

to 1.0 cm

as cysts.

shows

a large

pre-

numbers

(left

parasternal

transverse view) shows a large tumor (TH, arrowheads) with multiple disseminated cysts measuring 0.3-1.0 cm in diameter. C = heart. (c) CT scan obtained after radiation therapy shows a triangular residual thymic gland, the size of which is clearly larger than the age-related normal size (thickness of the left thymic lobe, 2.3 cm). (d) On the corresponding sonogram (left parasternal transverse view), the residual thymic gland (TH) has a hypoechoic internal texture. The cystic areas seen in b are no longer evident. AA = ascending aorta, TP = main

pulmonary

artery.

seen after chemotherapy for Hodgkin disease and other tumors (12). In all our patients with an initially normal thymus who underwent follow-up CT over a 20-month period (n = 7), no

sonography. This observation lates well with our experience that the normal adult thymus be delineated from surrounding

correso far cannot me-

diastinal

due

evidence of recurrent thymic plasia was seen. The comparison of sonograms CT scans showed the following

an inadequate nicity.

sults. In all patients thymus at CT (n gland from

Volume

could not surrounding 181

with

hyper-

a normal

the thymus be differentiated fatty tissue at =

#{149} Number

3),

2

and re-

tissue

at sonography difference

In all patients

with

to

in echoge-

thymic

enlarge-

ment diagnosed at CT (n = 15), sonography showed hypoechoic antenor mediastinal lesions that were clearly delineated from surrounding mediastinal

fatty

tissue.

Due

to the

predominantly globular configuration of these anterior mediastinal lesions, it was initially difficult to differentiate between an enlarged thymus and a lymph node tumor. The sonographic criteria at initial examination mdicated that the prevascular lesion was of thymic origin in only four of the 15 patients; a typical tongue-shaped configuration was seen on sagittal sonograms in two patients, and cysts within an anterior mediastinal globular mass were seen in two patients. Radiology

#{149} 381

a.

b.

Figure with

7. an

Focal involvement of the thymic inhomogeneous internal structure.

heads) within one hypoechoic ous

bulking

gland in a 19-year-old (b) Initial sonogram

the thymic bed (large arrowheads). TP = main pulmonary artery. (c) Initial node (L, small arrowheads) adjacent to normal hyperechoic thymic tissue of the thymic contours. A = ascending aorta, T = main pulmonary artery.

Follow-up sonography performed after therapy showed that all initially globular thymic tumors adopted a typical tongue-shaped configuration, indicating that the lesion initially detected node.

was not an enlarged lymph It is worth noting that all sono-

graphically detected thymic glands remained hypoechoic after completion of therapy and could be delineated from surrounding fatty tissue long after full remission (up to 17 months after therapy) (Figs 3, 6).

The drawn

following from our

normal

hypoechoic

conclusions findings:

may

be

(a) Normalsize thymic glands cannot be detected with sonography, and (b) thymic glands that are considered diseased because of size criteria at CT become sonographically visible due to an abechogenicity sonography

ence

of thymic

echo

(qualitative may indicate

disease

texture.

#{149} Radiology

The

criterion) the pres-

even

absence of thymic enlargement (quantitative criterion) at CT

382

C.

patient. (a) Initial CT scan shows (left parasternal sagittal view) shows

in the as illus-

at

sonogram (TH, large

trated in Figure 5. The results of this study also indicate that the changes in echogenicity observed in diseased thymic glands are identical to those seen in lymphomatous involved mediastinal lymph nodes with one exception: In contrast to mediastinal lymph node tumors, which disappear completely on full remission (13), an initially enlarged thymus remained identifiable at sonography because it had a different echo texture than the surrounding connective tissue. The significance of this finding in regard to the absence or presence of residual tumor within the thymus is uncertain. Why does the echo texture of the thymus persist? Although we evaluated all possible reasons, we did not

find an explanation tion. The persistence

for this of the

a roughly triangular two hypoechoic

observahypo-

echoic thymic texture is certainly not due to radiation therapy. Patients with lymphoma not originally involving the anterior mediastinum or patients with carcinoma of the lung who

(left parasternal arrowheads).

prevascular nodes (L, small

transverse The

node

tumor arrow-

view) produces

shows an obvi-

have undergone radiation therapy (not included in this study) never developed an abnormal echo texture of the thymus at sonography. Likewise, this phenomenon apparently does not portend an increase in the recurrence rate, since patients with and without recurrences had persistent hypoechoic thymic glands. The only cause of persisting hypoechoic texture of thymic glands seems to be prior involvement by Hodgkin disease. The sonographic criteria mentioned above may help in further characterization of equivocal anterior mediastinal lesions as demonstrated in Figures 3-5. In Hodgkin disease, thymic infiltration is most frequently diffuse, and rarely, if at all, focal as in infiltration of liver or spleen. In patients with marked (n = 3) or marginal diffuse (n = 1) enlargement of the thymus seen at CT, sonography tiple, hypoechoic nodules nor mediastinum, which

showed mulin the antewere shown

November

1991

to lie within the thymic bed when correlation with CT scans was performed (Figs 5, 7). We assume that these findings suggest the presence focal thymic lymphomatous involvement. In patients with extensive lymphomatous involvement of the thy-

mus,

a residual

and

frequently

of

en-

larged thymic gland is often detected after therapy (Fig 2, Table 2). Except for one residual enlarged paratracheal lymph node, all residual mediastinal tumors persisting after therapy in our patient group were due to residual enlarged thymic glands. This observation supports the hypothesis by Katz et al (14), which states that residual mediastinal masses found after treatment of Hodgkin disease are the re-

sult

of thymic

our patients glands after frequency of The clinical involvement phoma-particularly immunologic

prognosis-is

enlargement.

None

of

with enlarged thymic therapy showed a higher subsequent relapse. significance of thymic in Hodgkin lymregarding its role and its influence on

as yet unclear.

consequences concerning whether an anterior mediastinal mass represents involved lymph nodes or involved thymus. This study was designed to provide new information, which, although perhaps currently without clinical or management importance, might provide data that could influence patient treatment. In our study, patients both with and without thymic involvement showed similar rates of recurrence: 25% for patients with

CT evidence and

for

ment

regimen

2.

3.

#{149} Number

2

during

the

11.

can sugbe examof patients, basis. U

thymus

gland.

Cancer

1974;

Pnndull

G, Beck

W, Rahlf

Hodgkin’s

disease

and

mor.

Pediatr

1983;

EurJ

G, Gadner

H.

a mediastinal

141:117-1

JE, Nicholas

tu-

19.

12.

Kissin CM, Husband

13.

smann W. Benign thymic enlargement in adults after chemotherapy: CT demonstration. Radiology 1987; 163:67-70. Wernecke K, Vassallo P, Hoffmann C, et al. Value of sonography to monitor the therapeutic response of mediastinal lymphoma: comparison with chest radiographs and

D, Ever-

CT. AJR 1991; 156:265-272. 14.

BI. Hodgkin’s disease, autoimmunity, and the thymus. Br Med J 1965; 1:1592-1596. Keller AR, Castleman B. Hodgkin’s disof the

145:249-254.

Heron CW, Husband JE, Williams MP. Hodgkin disease: CT of the thymus. Radiology 1988; 167:647-651. Wernecke K, Peters PE, Galanski M. Mediastinal tumors: evaluation with suprasternal sonography. Radiology 1986; 159:405-409. Wernecke K, Potter R, Peters PE, Koch P. Parasternal mediastinal sonography: sensitivity in the detection of anterior mediastinal and subcarinal tumors. AJR 1988; 150: 1021-1026. Moore AV, Korobkin M, Olanow W, et al. Age-related changes in the thymus gland: CT-pathologic correlation. AJR 1983; 141:

241-246.

first

we

Hoffbrand

Katz

M, Piekarski

JD, Bayle-Weisgerber

CH, et al. Masses mediastinales residuelles post-radiotherapiques au cours de la maladie 1977;

de Hodgkin.

Ann

Radiol

(Paris)

20:667-672.

33:

1615-1623.

4.

Baron mus.

181

used

Thomas F, Cosset JM, Cherel P, Renaudy N, Carde P, Piekarski JD. Thoracic CTscanning follow-up of residual mediastinal masses after treatment of Hodgkin’s disease. Radiother Oncol 1988; 11:119-122.

ease

9.

10.

References 1.

8.

follow-up,

part of the study period, gest only that our findings med with a larger number possibly on a multicenter

Lindfors KK, MeyerJE. Thymic cysts in mediastinal Hodgkin disease. Radiology 1985; 156:37-41. Francis IR, Glazer GM, Bookstein FL, Gross BH. The thymus: reexamination of age related changes in size and shape. AJR 1984;

7.

without

(clinical

RL, LeeJKT,

Computed

Volume

patients

6.

involvement

thymic 4-55 months; mean, 28 months). Because of the small number of patients studied and the nonstandardized treat-

involvement

With

current staging and management, the thymus is considered to be a “lymph node” and, therefore, its involvement does not change the stage to an or “IV” stage. Likewise, there are no radiation therapy or chemotherapy

20%

of thymic

5.

Sagel 55, Peterson

tomography Radiology 1982;

of the normal 142:121-125.

RR. thy-

Radiology

#{149} 383