Reprinted from Ci.IpcAL. NucAx MEDIC.INr April 1993ml. is, No. 4© J. U. Lippincott C0. Printed iii USA,

Spurious Lung Metastases on F?adioiodirieThyroid and Whole Body Imaging

SIEMA 5AKHEET, M.D., AND MUHAMMAD M. HAMMAMI, MO., PH.D., FACPt

In patients with differentiated thyroid cancer, radiolodineuptake in the area of the lung usually denotes metastasis; however, It could represent an uptake by unrelatedpulmonary disease or by the breasts, or external contamination. In this study, 22 foci that simulated lungmetastasis on 11 thyroId and whole body scans wereproven not to be metastasis by relmaging after cleaning(15 focI), or were strongly suspected to be due to extet.nal contamination because of the featores of other Images (7 foci).

All foci were noted only on anterior views of the chest.Of the 22 focI, 19 were local, two were smeared, end onewas lobar. Foci were multiple in 7 scans, unilateral in 10scans, and were associated with other artifacts In 4scans. Caution should be used in interpreting apparentpulmonary radlolodine uptake as lung metastasIs; reimaging alter cleaning the skin and changing garmentshould be obtained when the uptake is confined to anterIor views of the chest and/or when its pattern Is atyp

RANOIOOTNE UPTAKE TN the lung usually indicatespulmonary metastases from differentiated thyroid

cancer. However, several cases of lung uptake havebeen reported in the literature that have proven to be

due to unrelated benign (1—3) or malignant (4—6) disease. Physiologic uptake by lactating breasts (7) mayalso be mistaken for Jung metastases. Furthennore.

one case of skin contamination with sputum in a patient with a tracheostoiny that simulated a lung metastask has been reported (8)- We present 22 foci of skinand/or garment contamination that mimicked pulmonary metastases on II radioiodine scans and we de

scribe their pattern.

Received for publication August 27, 992; revision accepted November It. 1992.

Reprint requests: Sienia Bakheet, M.D., Consultant. NuclearMedicine, Dept. of Radiology MLIC2S, King Faisal Specialisi Hospitu and Research Cenire. P.O. Box 3354, kiyadh If’. SuIiAlobia.

From the Departments of Radiology and Medicine, t kingFaisal Specialist Hospital & Research Centre, Riyadh,

Saudi Arabia

.Tateriu1s and Methods

King Paisal Specialist Hospital and Research Centre is areferral center for the management of thyroid cancer inSaudi Arabia, Patients are managed according to an established prolocol that includes diagnostic thyroid and wholebody scans six eeks after thyroidecton-.y and within oneyear of 1-131 trealn,ent, as well as a routine poslablalion

scan Spot images of the head and neck (anterior and poste

for), chest (anterior and posterior,, and the pelvis (anterior)are routinely acquired for 300000 counts or 10 minutes usinga large field of view gamma cameras (GE400, Wisconsin,USA) and appropriate collimator (medium energy for 1-123and high energy for 1-131). Images are taken 24 hours afterthe ingestion of a 185 MBq (5 mCi) 1-123 capsule (locallyproduced in our research center) for diagnostic scans and

again approximately three days alter the administration of1-13? treatment capsules when isolation in the hospital is nolonger needed (exposure rate <1.8 mR/br at 3 feet) for postablaLion scans. Timing of the posrabiatiop scan is based onpracticality, as must of our patients live very far horn ourcenter. Patients are instructed to take a shower and changetheir garment twice daily after the administration of 1-131capsules, and before obtaining postabiation scans.

‘When an apparent ung focus on the anterior view of the

chest is no, seen on the posterior view. it has been ourpractice (since 939) to clean the skin and change the ga,

ments of a patiei, and take a second anterior nave toconnrm the possibility of external contamination. By doingthis, 5 mci on 8 scans (Fig. I—SI were identified over aperiod oC 3 years (Aug 1989—July 1992). During this period.a total of roughly 2000 diagnostic and postablation scanswere performed in our center. 0 the scans performed beforeAugust 1989, three were false positive (Figs. 9—I I) Thenahire ofthe false positive uptake in the lungs in these scanswas strongly suspected because of the results of other studies as detailed under results and discussion.

All our patients (19—58 years old) hid differentiated thyroid cancer anti were otherwise healthy. [here were sixdinostic and five poslablation scans.

cal.

307

hiMi,.i 6r !,1. -

A

F9, . (A) An anleoc wew c4 b’.e cnesla O-year-o female stows a tcai area ô

activity (arrow) in The right lower Jobe m,m‘cks Jung metastasis. 8) Repeat anterior‘jaw or The chest after changing garmentshuws the disappearance of the focus thatwas due to a contaminated paper tissue inhe blouse pocket.

Fig. 2- A) An anterior view of the chestin a 58-year-old female shows three foci ofaint activity in the right lower abe (arrows)

That mirnick lung metastases. (B) A postcleaning anterior view of the chest demonstrates the disappearance of all foci.

Fig. 3. (Aj N ar,tero vi of The readand chest i, a 3-yaar-o fa e. Thesrnoaroc actMty n tie efi Joper obe (rrow) n-wgnt be corIaminatn. { Posicleanng anterior view of the chest ,nstra,esdsappearance & Me reared activityThere is a tiny suoerfiaI focus in he s<ulFat nst ike w ewesents aroThe contamnation artifact.

Fq 4 A) Ni a.’le’ic’ view r The headard nest cia 19-vea-obi anlaIe The redial arrow points a a Iocai area of acovitymimicking lung metastasos n the ott uoperahe The laterat arrow points to another contarmnation artifact mimicking shoulder meastasis 9) Postcleaning anterior view ofhe chest demonstrates disappearance ofxth foci

April 1993 Vol. 18CLINICAL NUCLEAR MEDICINE

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308

A

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1.X %

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No. 4 SPURIOUS LUNG METASTASES • Bakheet and 1-lammami 309

Fig. 5. (A) An anterior view of the chestn a 31 -year-old emale shows two foci ofactivity mimicking lung metastases lblack arrOwS) in the left lower lobe, and another nramination outside body contour {open SF‘owhead). No foci are present in a (B)postcleanlng anterior view of the chest.

:ig 5. A) An anterior view of the chestri a 46-year-old female shows two foci (arrows) in ho right ung base/right upper ouad‘ant of the abdomen arid one focus in the leftupper lobe mimicking ung metastases. (B)Postoleaning anterior view of the chest demonstrates complete disappearance of all foci.

Results and Discussion

The characteristics of II scans showing 22 externalcontamination artifacts that mimicked lung metastasesare summarized in Table I and presented in Figures—il. On eight scans (Fig. 1(A)—8(A)) 15 foci were

suspected to represent external contamination because they were not seen on posterior views of thechest. This deduction was proven as they did not appear on postcleaning images (Fig. 1(B)—6(B), 3(B)). InFigure 9(A) and 10. 5 foci of external contaminationare shown on anterior views of the chest. Postcleaningreimaging was not performed in these cases. However,follow-up studies showed the absence of these focidespite the unchanged appearaice of the thyroid remnant (Fig. 9(8)). This, together with the fact that theinitial scans were performed with 1073 MBq (29 mCi)of 1-131, a small dose that is not xpected to ablateung metastases, strongly suggest that these Ibci are

artifacts. Similarly, the 2 smeared foci in Figure 11(A)were not seen in a similar study performed 3 monthsearlier (Fig. 11W)).

Except for one focus of obar distribution (Fig. 3)and two foci of smeared activity (Fig. 11) that weresuggestive of contamination, all other foci could havebeen easily mistaken for pu’monary metastasis. It is

interesting to note that in Figure 7(A), there were threefoci due to external contamination and one focus ofreal metastasis. This would have been impossible toidentify if not for the postdeaning reimaging thatshowed the disappearance of contamination and the

Fig. 7. Ai anterior view of the chosi n a 58-year-old femaleshows three foci of activity (arrows) in the right lower lobe mimickingung rnetastases. ArTowhead de’ineates reai lung metastasis (thatwas also seen on a previous diagnostic scan). A postceaning ante•ior view ol the cnest showed disappearance of the three contamination artifacts and the persistenco of the real lung metastasis (notshown).

rLI

£2

Fig. B (A) An anterior view of the chestn a 50-year-oJd male shows focal area of

acMty rrow; r The e’t Icwei .ote mrisk

.rg trig 7etastases. A-rowriead shows in

a eso*ageai aol vy (8) Pcsc1eariro

Wa ‘s:eaflrc afield yew of Pa ie

shows disappearance of both foci.

g 9- 4) An antehu, vw of fle neat

and chest in a 48-year-old ‘emale shows

tree foci in the eli upper lobe mimicking

lung metasrases. Arrowheads oint to hot

markers. (0) An anterior view of the chest on

a repeal study after B months using 185 MBq

til- !23. The disappearance ci the three (ccl

esite the uricnar.ged apseararlee of tne

tyroid remnant Strongly SU99OSIS contan’i

‘at on.

persistence of metastasis. Although prior diagnostic

scan showed oniy a single foci of real metastasis (notshown), it could have been argued that this was due to

a lower sensitivity of the diagnostic scan.

The use of radioiodine thyroid and whole body scan.

t (S !r,2

0. 4.g. anlelor v ow of the head and chest n ‘t’-year-o

female shows Mu roci of activity (arrow) in he left upper ‘obe

mimicking lung rnelastases. Arrownead ocints to thyroLd remnant. A

zhest radiograph performed at the same time showed clear lung

ields. A follow-up study performed with 185 MBq nfl-i 23 showed

he disappearance DI the foci and he nchanged appearance of the

Thyroid remnant.

in general, is very beneficial in detecting lung ,netas

tasis ri patients with differentiated thyroid cancer (3).

However, both false negative (9) and false positive

(1—3) cases have been reported. Pulmonary metastases

of thyroid cancer can he mimicked on radioiodine

whole body scans by an uptake by lactating breasts

(7). which is most confusing when it is asymmetrical(8): an uptake by inreated lung esions such as

chronic inflammatory lung disease (2), fungal infection

3), pulmonary adenocarcinoma 4), large cell bron

chogenic carcinoma (5), and disseminated gastric can

cer (6): congenitai anomaly such as pectus excavatum

(I); or, as in our study, by external contamination of

the chest wall or the garment.External contamination artifacts that mimicked

bone metastnsis (10), shoulder menistasis (II), lung

mets1asis (8), or that simuJated radioactive wg (12),

have been reported. The source of conrnmination in

these cases and in our patients is most likely radioio

dine normally excreied in body secretions such as

sailva, nasal secretion, and sweat (13).The predictive value of a positive radioiodine uptake

n the lung for pulmonary metastasis from thyroid can

cer is not known. However, we estimate that external

coniamination as a cause of spurious king metastasis

310 CLINICAL NUCLEAR MEDICINE April1993 VOL 18

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No. 4 SPURIOUS LUNG METASTASES • Bakheet and Hammarni 311

F y. 1 A; Ai an,ero knew of The heasar$ ctest ir a 52-year-ot female sho-.vs lotfoci (arrows) of smeared activity in the leftupper lobe mimicking lung motastase& (B3An anterior view of the chest of a study per-armed three months earlier with 1073 MBq

-131 reveals the absence of both foci.

can be seen in about 0.4% of radioiodine thyroid andwhole body scans. We obtain images at about threedays after 1-131 therapy when isolation is no longerneeded and the patient can be discharged home. Delaying imaging to 5 or 7 days after 1-131 therapy mayreduce the incidence of artifacts due to external con

tamination. However, this is inconvenient for patients

iving far away rrom the medical center, as is the caseof most of our patients.

Differentiating real from spurious ung metastasis ona radioiodine scan is often challenging. Failure of theposterior views to show the foci, the unilateral clustering of the foci, or the presence of other contamination artifacts, togeiher with the absence of a compat

CD — Complete disappearance.RI = Repeat ImagaRS = Repeat StudyPS = Previous Study.

TABLE 1. Characteristics of Spurious Lung Metasrass Due to Exlernal Contamination

I

A

Dose Pattern Proof ofTracer (MDq) (P of Foci) Site Contamination Comments

I. i-i 23 165 Fcca! 1) RLL Prospective Due to tissue paper in the pocketCD RI

2. -123 185 Foca (3) RLL ProsectveCD. RI

3. -I 23 185 Lobar ii LUL °rosiectlve Additiona contarninajon r rioCD’RI rqa cf tie SKLJI

4. 1-123 Foca 1) LUL ‘osective Addili ora’ conla,rina:ion fl heCD Al area of the eft sioulse’

5. -I 3 ISO Fccai (2 ‘osoetve Additional cortarrinatior’ cutsideCDRI body car totr

6. -123 65 ocaI (2) RLL roscective —

(1) LUL CDiRI7. -131 7400 csa’ (3) P.LL ‘rosoeclive oncotapt real ung metaslass

CD RI8. -123 1 B5 Fatal 1 LLL 2rospjve Mtitonal artifact in the redasti

CDAI num due to esophagea; retenon of radioodfrie

g. lS 073 acai {3 LUL Rai:osoective U,charied apearan of thyrocCD RS omra,t Cr RS

0. -13 1D73 Foca 2) tAiL Ret’os,ec:We Nornai c1est radiogrs4-. LiCD AS tangec appea’an c4 fl,oid

remnant on RS-131 073 Smeared (2) LUL Prospeciive —

CD/PS

ELL LUL, LLL Right Lower, Left Upper, and Left Lower Lobe, respectively.

312 CUNICAL NUCLEAR MEDICNE April 1993 Vol. 18

ble clinical picture should raise the suspicion of a caseof false-positive lung metastasis and mandate reimaging after garment change and skin cleaning.

Acknowledgment

The authors thanx Luz Bancale for her secretasial assistance ii

the preparation of this manuscript.

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