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norm al thyroid pertechnetate im age or a thyroid im age with a

cold area corresponding to the area w ith increased focal uptake

w ith tetrofosm in and sestam ibi supported the parathyroid ade

noma conclusion. M oreover, most parathyroid adenoma pa

tien ts are eld erly w om en , am ong w ho m irregu lar stru ctu re in th e

thyroid gland is a frequent phenom enon. T herefore, though not

experienced in this study, thyroid scintigraphy m ay also elim

in ate fa lse -p ositiv es c au se d b y m isin te rp re ta tio n o f te tro fo sm in

o r sestam ib i u pta ke in th yro id ad en om as. In acco rdan ce w ith th e

recom mendations from H indie et al. (4) and R ossitch et al. (7),

knowledge of the thyroid anatom y should im prove the scinti-

graphic interpretation. H ence, irrespective of w hich of the tw o

par at hy ro id p re pa ra ti on s th at is p re fe rr ed , we s tr ongl y r ec ommend

th at th yro id s cin tig ra ph y b e in clu de d in th e p ro ce du re .

T wo of the 4 false-negative scintigraphic results w ere from

investigations on patients w ith relatively sm all parathyroid

adenomas: 0.16 and 0.23 g (Table 2). The patient w ith the

0.16-g adenom a had a thyroid scintigram indicating m oderate

m ultinodular goiter, while the other had a com pletely norm al

thyroid gland. A third patient w ith negative scintigraphy had a

large adenom a of 1.37 g situated behind a m ultinodular goiter.

W hen the scintigram s of this patient were revised postopera-

tively, w e realized that the adenom a actually w as visible.

F urth er inv estig atio ns are in p rog ress in ou r lab oratory , w ith

the intention to improve the image resolution and to find a

sim ple and reliable sam e-day procedure for parathyroid scin

tig ra ph y w ith y 9r T c-la be le d te tro fo sm in a nd th yro id s cin tig ra

phy wit h WmTc-pe rt echne ta te .

CONCLUSION

Tetrofosm in is an alternative to sestam ibi for parathyroid

scintigraphy. H ow ever, am ong the 16 patients in this study, the

thyroid-parathyroid differential w ashout of sestam ibi previ

ously reported by other authors was never observed with

tetrofosm in. M oreover, differential w ashout of sestam ibi w as

not seen in 5 of 11 scintigraphically positive adenom as in the

neck, and is, therefore, not a reliable diagnostic criterion.

Irre sp ec tiv e o f th e p re pa ra tio n p re fe rre d fo r p ara th yro id v is ua l-

ization-sestam ibi or tetrofosm in-com bination w ith thyroid

scin tig rap hy seem s m an dato ry . F urth er stu dies are nec essary to

o ptim ize th e pro ced ure fo r sc in tig raph ic detectio n of p arath y

roi d l es ions.

ACKNOWLEDGMENTS

W e th an k S ig ne E lise T j0n nelan d and the te chn ica l staff o f th e

Sec tio n o f Nucle ar Medi cin e, R ik shos pi ta le t, T h e Na tio na l Ho sp i

ta l o f N orw ay , fo r e xp ert te ch nic al a ssista nc e.

REFERENCES

1 . C oa kley A J, K ettle A G, W ells C P, O 'D oh erty M J, C ollin gs R EC . T ech ne tiu m-9 9m -

s es ta mi bi : a n ew a ge nt f or p ar at hy ro id im ag in g. N uc Med Commun 198 9; 1 0: 79 1 -7 94 .

2. O 'D oh erty M J. K ettle A G, W ells P . C ollins R EC , C oakley A J. P arathyro id im aging

w ith te ch ne ti um -9 9m -s es ta mib i: p re op er at iv e l oc al iz ati on a nd ti ss ue u pt ak e s tu die s.

J N u c-Me d 1 9 92 :33 :31 3 3 1 8.

3. T hule P , T hakore K , V ansant J. M cG arity W , W eber C , P hillips L S. P reoperative

l oc al iz at io n o f p ar ath yr oi d t is su e w it h W m Tc -s es ta mi bi I 23 I s ub tr ac ti on s ca nn in g.

J C li n E nd oc r M el ab 1 99 4; 78 :7 7 8 2.

4 . H in die E , M e lli er e D , S im on D , P er le mu te r L , G all e P . P ri ma ry h yp er pa ra th yr oi di sm :

i s t ec hn eti um 9 9m -s es ta mi bi /i od in e- 12 3 s ub tr ac ti on s ca nn in g t he b es t p ro ce du re t o

l oc at e e nl ar ge d g la nd s b ef or e s ur ge ry ? J C li n E nd oc r M e la b 1 99 5: 80 :3 02 -3 07 .

5 . W ei J P, B urk e G J, M an sb erg er A R J r. P re op erativ e im ag in g o f ab no rm al p ara th yro id

g la nd s i n p at ie nt s w ith h yp er pa ra th yr oi d d is ea se u si ng c om b in at io n T c- 99 m- pe rt ec h-

n et at e a nd Tc -9 9m - se st am ib i r ad io nu cl id e s ca ns . A n n Su rg 1 99 4: 21 9: 56 8 -5 72 .

6 . T ai ll ef cr R , B ou ch er Y . P otv in C , L am be rt R . D et ec ti on a nd l oc al iz at io n o f p ar at hy ro id

a de no ma s i n p at ie nt s w it h h yp er pa ra th yr oi di sm u si ng a s in gl e r ad io nu cl id e i ma gi ng

p ro ce du re w i th t cc hn et ium -9 9m - se st am ib i ( do ub le p ha se s tu dy ). J N u c Med I 99 2; 33 :

1801-1807.

7. Rossitch JC, Cow an RS, Ellis M B. Griffith RF. Technetium -99m -sestam ibi for

d et ec ti on o f p ar at hy ro id a de no m a. C om pa ri so n o f s in gl e a nd d ua l t ra ce r i ma gi ng . C li n

N u c -Me d 1 9 9 3:2 0:2 20 2 2 1 .

8. Kelly D, Forster AM , Higley B, et al. Technetium-99m-tetrofosmin as a new

r ad io ph armac eu ti ca l f or myoc ar di al p er fu si on imag in g. J Nu c Med 1 9 93 :3 4: 22 2- 22 7 .

9 . H ig le y B , Sm it h FW , Sm it h T , e t a l. T e ch ne ti um -99m -l ,2 -b is [b is (2 -e th o xy et hy l) ph os -

phino]ethane: hum an biodistribution, dosim etry and safety o f a new m yocardial

p er fu s io n imag in g a ge nt . J N u c Med 1 99 3 :3 4 :3 0 -3 8.

10. Ishibashi M , Nishida H , Kum abe T , M onta S, M atoba F, Nom ura G , Hayabuchi N.

T c- 99 m- te tr of osmi n. A n ew d ia gn os ti c t ra ce r f or p ar at hy ro id im ag in g. C li n N uc Med

1995:20:902-905.

Comparison of Parathyroid Im aging with

Technetium-99m-Pertechnetate/Sestamibi Subtraction,

Double-Phase Technetium -99m-Sestam ibi and

Technetium-99m-Sestam ibi SPECT

Charles C. Chen, Lawrence E. Holder, W illiam A. Scovili, Ann M . Tehan and Donald S. Gann

D ep ar tm en ts o f R ad io lo gy a nd S urg er y Un iv ers ity o f M ar yla nd M ed ic al S ys te m B altim ore M ar yla nd

The ab il it y o f 99rTTc -pe rtechne ta te /ses tam ib i sub trac ti on , double-

p ha se 9 9m Tc -s es ta mib i a nd 9 9n rT c-s es ta mib i SPECT im ag in g to

localize abno rm al p arath yroid tissue w as com pared. M eth ods:

F if ty -f iv e c on se cu tiv e p at ie nt s h ad par at hy ro id imagin g b ef or e s ur

gery for hyperpa ra th yroidi sm . Imag ing consisted o f Tc -per te ch -

netate pinhole im ages of the neck follow ed by Tc-sestam ibi

p in ho le image s o f th e n ec k a nd para lle l- ho le image s o f th e n ec k a nd

c he st (e arly im ag es ). W ith in 2 .5 -4 .0 h r la te r p in ho le im ag es o f th e

neck, pa ra llel-ho le and S PE CT im ages of the neck a nd chest w ere

o bt ain ed ( la te image s) . Nodula r f oc i o f in cr ea se d s es tam ib i a ctiv ity

w ere c on sid ere d a bn orm al. R es ults : T he s en sitiv ity fo r a bn orm al

parathy ro id g lands by v isua l compar ison o f ea rl y images and per te ch -

R ec eiv ed J ul. 2 2, 1 99 6; r ev is io n a cc ep te d N o v. 6 , 1 99 6.

F or co rre sp ond enc e o r re prin ts co ntact: C harle s C . C he n, M D, D epa rtm en t of

R ad io lo gy , S a in t F ra nc is M e dic al C en te r, 5 30 N E G le n O ak A ve ., P eo r a ,L 6 16 37 .

neta te image s was 72 - 7 5 , la te image s a nd pert ec hn et at e image s

was 73 -78 and doub le -phase (ea rl y and late) ses tam ib i images

w as 62 -6 5 ; com puter subtra ction of p ertechne tate fro m early

im ag es was 7 1 -7 4 ; a nd SPECT im ag in g was 7 9 . T he s en sitiv

it y f or p ar at hy ro id a de nomas was 89 -9 8 , whi le th e s en sit iv ity f or

h yp erp la stic p ara th yro id g la nd s was o nly 4 7 - 58 . C on clu sio n:

L ate im ag in g, c om pu te r su btra ctio n a nd SPECT m ay n ot b e n ec es

sary since they provided only m arginal im provem ents on visual

c ompar is on o f e ar ly s es tam ib i w it h p er te ch ne ta te image s. Doubl e-

ph ase se stam ibi im aging w as less sensitive, so baseline thyroid

imag ing w i th per te chne ta te i s recommended .

Key Words: parathyroid;hyperparathyroidism;echnetium 99m ses

tamibi; technetium-99m-MIBI

J N uc -Med 1997; 3 8: 83 4 8 39

83 4 T HE JO UR NA L FN UC LE ARM E DIC IN Eol 3 8 o 6 u ne 9 97

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Ihe accepted radionuclide method for imaging abnormal

parathyroid tissue w as the dual-tracer subtraction technique

usin g 9 9m Tc-p ertech ne tate an d 2 01T 1 th allo us ch lo rid e (7 ,2 ).

H ow ever, since the introduction of 99m Tc-sestam ibi as a para

thyroid im aging agent (3,4), various im aging protocols have

b een in tro du ced (3 ). T he d ifferent p ro toc ols can be categ orized

into the single-tracer double-phase (early and late) 99mTc-

s estamib i im ag in g te ch niq ue v ersu s th e d ua l-tra ce r su btra ctio n

te ch niq ue s o f 9 9mT c-s estamib i/'2 3I io din e o r 9 9mT c-se stamib i/

99mTc-pertechnetate.

Prelim inary reports suggested that the sestam ibi m ethods

w ere e qu al o r su pe rio r to th e 9 9nTc -p erte ch ne ta te /2 01Tl su btra c

tion technique (3). However, there have been few direct

com parisons of the single-tracer and dual-tracer sestam ibi

tech niq ues. T he cu rren t stu dy p resen ts th e resu lts of an im aging

p ro to co l tha t ev alu ated bo th sin gle-tracer an d d ual-tracer tech

niques, as well as SPECT.

MATERIALS AND METHODS

Patients

S ix ty -s ix c on se cu tiv e p atie nts r ef er re d to two exper ie nc ed endo

c rin e su rg eo ns a t th e U niv ersity o f Mary la nd Med ic al S ystem from

M arch 1993 to October 1995 had parathyroid im aging before

su rge ry fo r h yp erp arath yro id ism . O f th ese p atien ts, 1 1 de clin ed

surgery. T he rem aining 55 patients had surgical cures and w ere

included in this study. O ne surgeon perform ed 28 and the other

s urg eo n p erfo rm ed 2 7 o f th e o pe ra tio ns .

Imaging P ro toco l

Ten to 15 min after injection of 74-111 MBq (2-3 mCi)

99m Tc-pertechnetate, 5-m in pinhole im ages of the neck w ere

o btain ed . W ith ou t m oving th e p atien t, 74 0-92 5 M Bq (2 0-25 m Ci)

9 9mT c-se stamib i w ere in je cte d fo llowe d b y se qu en tia l 5 -m in p in -

hole images of the neck for a total of 30 min and a 5-min

p arallel-ho le im ag e of th e n eck an d chest (early im ages). W ith in

2.5-4.0 hr later, a 5-min pinhole image of the neck, a 5-min

p arallel-ho le im ag e o f th e n eck an d ch est an d S PE CT im ag es (6 4 X

6 4 m atrix , 64 step s, 20 sec p er step ) w ere ob tained (late im age s).

C ompu te r su btra ctio n o f th e 5 -m in p in ho le p erte ch ne ta te im ag es

from the 5-m in pinhole im ages at 30 m in postinjection of 99m Tc-

ses tamib i were per fo rmed .

Scan Interpretat ions

Interpretation of scintigraphic im ages was perform ed by a

nuc le ar medic in e phy sic ia n b li nd ed t o th e s ur gic al re su lts , i ni tia ll y

c ompar ing th e p er te chne ta te image s w ith th e e ar ly , l ate , c ompute r-

su btra cte d a nd SPE CT se stamib i im ag es . T he e arly a nd la te im ag es

w ere th en re an aly ze d w ith ou t th e b en efit o f th e 9 9mT c-p erte ch ne -

tate im ages 3 m o later.

A ll image s wer e d ig ita l a nd d is pla yed on a compute r wo rk st atio n

for analysis in random order. ROIs were drawn over areas of

in cr ea se d upt ak e cor re sponding t o abnorma l p ar athyr oid tis su e and

co mp are d to an R OI o ver n orm al th yroid p aren ch ym a. A bn orm al

parathyroid/norm al thyroid sestam ibi uptake ratios w ere then

c alc ula te d from e arly a nd la te p la na r im ag es.

P hy sio lo gic C rite ria fo r A bn orm al P ara th yro id T is su e

F oci of increased activity identified on sestam ibi im ages in

excess of that seen on pertechnetate im ages were considered

pos itiv e f or a bnorma l p ar athyr oid t is su e. Image s wer e i nte rp re te d

as having definite, suggestive, equivocal and absent foci of

a bn orm al p ara th yro id tiss ue u pta ke . F or c orre la tio n w ith su rg ic al

a nd pathol og ic al re su lts , d ef in it e a nd s ugge stiv e f oc i we re c on sid

ered po sitiv e, w hile eq uiv ocal an d ab sen t foci w ere con sid ered

negative.

W hen early and late (double-phase) planar sestam ibi im ages

w ere co mp ared to ea ch othe r w ith ou t the in fo rm atio n p ro vided b y

p erte ch ne ta te im ag es , fo ci o f a ctiv ity w ere c on sid ere d p os itiv e if

they were increased relative to thyroid tissue on early or late

im ag es, o r b oth .

A nato mic C riteria fo r A bn orm al P ara th yro id T is su e

Nodular foci of sestam ibi uptake clearly separate from the

th yro id g la nd w ere c on sid ere d a bn orm al. T he se fo ci n ee d n ot h av e

upta ke g re ate r th an norma l th yro id t is su e t o b e con sid er ed pos itiv e.

S PE CT can help to isolate foci of parathyroid tissue from super

im posed thyroid tissue. H ow ever, due to the spacial resolution

lim its o f SPE CT im ag in g, n od ule s o f a bn orm al p ara th yro id tis su e

m ay m anifest as only focal bulges in the contours of the thyroid

gland.

Statis tica l Analys is

A ll d ata a re e xp re ss ed a s m ea n 1 s .d . E stim ate s o f s pe cific ity

w ere b ased o n the assu mp tio n th at eac h patien t had fo ur p arath y

roid glands plus any ectopie parathyroid glands identified at

s ur ge ry . P ai re d S tudent's t- te sts wer e u se d to compar e p ar athyro id /

t hy ro id s es tam ib i upta ke ra tio s.

RESULTS

Of the 55 patients who had surgical cures, 46 had primary

hyper pa ra thyr oi di sm , e ight h ad s econda ry hyper pa ra thyr oid ism

(e nd -s ta ge re na l d ise ase ) a nd o ne h ad te rtia ry h yp erp ara th yro id

ism (e nd -stage ren al disease b ut h ad a ren al transp lan t). T wen ty

(36%) were men, and 35 (63%) were women. The men were

52 12 yr old (range 30-77 yr), and the women were 55 14

yr old (range 27-79 yr).

The mean serum calcium decreased from 11.2-9.1 mg/dl

after su rg ery in p atien ts w ith prim ary h yperp arath yroidism an d

fro m 10 .7-7 .6 m g/d l in p atients w ith seco ndary h yperp arath y

roidism . The mean serum phosphate levels increased from

2.6-3.3 m g/dl in prim ary hyperparathyroidism patients and

d ecreased in seco nd ary hy perpa ra thy ro id ism pa tien ts fro m 7.3-

6 .5 mg/d l.

Forty-eight (87% ) of the 55 patients were evaluated before

in itial su rg ery . F orty -o ne p atients h ad p rim ary h yp erp arath y

ro id ism , six h ad se co nd ary h yp erp ara th yro id ism a nd o ne p atie nt

had tertiary hyperparathyroidism . There were 17 m en and 31

wom en. The m en were 54 12 yr old (range 30-77 yr), and the

women were 56 14 yr old (range 27-79 yr). One patient had

a m ix ed p ap illa ry -follicu lar th yro id carcino ma th at w as v isib le

as a hypofunctioning mass on both the pertechnetate and

sestam ibi im ages (F ig. 1)

T he o th er sev en ( 1 3% ) p atien ts w ere referred for reo perativ e

surgery. Five had prim ary hyperparathyroidism , and tw o had

seco ndary h yp erp arath yroid ism . T here w ere th ree m en an d fo ur

women, ages 42 9 yr old (range 31-60 yr). Two of these

patients were found to have ectopie parathyroid activity on

im aging, and parathyroid adenom as w ere excised. O ne patient

w as found to have a parathyroid carcinom a involving the left

thyroid gland (Fig. 2). One patient had M EN I syndrome and

w as found to have a 400-m g hyperplastic parathyroid gland that

also was visible on imaging. The other three patients were

found to have sm all parathyroid adenom as less than 100 m g in

size (two of these were visible on imaging). The smallest

parathyroid adenoma detected on imaging was 88 mg. The

sm allest hy perp lastic p arath yro id gla nd id en tified w as 1 30 m g.

The results of planar sestamibi imaging with and without a

99m Tc-pertechnetate im age in 55 patients w ho had surgery are

listed in Table 1. There were an estimated 227 possible

parathyroid glands in this group of patients, four per person in

5 5 p atien ts an d sev en ecto pie p arath yro id ad en om as.

PARAT HYROIDMAGINGCOMPAR ISONh en e t a l. 8 35

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TABLE 3

Parathyroid Adenoma/Thyroid Activity Ratios

Pattern No. Early ratio range)

Late ratio range) Rvalues

ADashinAD

persistAD

washoutHG

washinHG

persistHG

washoutECT

ADashinECT

AD persist1539916231.09

0.19 0.75-145)1.09

0.14 0.94-121)127

0.141 .10 - 1 . 54 1 . 09

0.24 0.77-137)0.971.1

7 0 .3 6 0 .6 3- 158)0.78

0.400.75-0.80)0.54

0.11 0.44-0.65)1.32

0.35 0.91-2.04)1.09

0.13 0.95-121)1.11

0.11 0.99-1.26)1.34

0.17 1.10-156)0.981.08

0.38 0.53-144)1.21

0.20 1.07-1.35)0.54

0.10 0.45-0.64)C0.003ns

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TC99M

M IBI 15M IN

SUBTRACT ION

3HP

F IG UR E 5 . P a tie n t w ith tw o p a ra th yr o id a de n om a s , th e r ig h t o n e w as 8 02

m g and th e le ft w a s 3 8 2 m g, bu t o n ly th e rig h t g la n d w a s id e ntifie d o n

im a g es . (U pp e r le ft) T e ch ne tiu m -9 9m -p e rte c hn e ta te im a g e , (u pp e r rig ht)

e arly T c-s e s ta m ib i im a ge , (lo we r le ft) c om p ute r-s ub tra ctio n im a ge a nd

(lo w er rig ht) la te T c-s e s ta m ib i im a g e.

In addition, the rationale for double-phase imaging suggested

by Taillefer et al. 6) of slower washout of 9 mTc-sestamibi

f rom parathyroid adenomas relative to thyroid tissue was not a

universal physiologic phenomenon in our study group. Rapid

washout of sestamibi f rom parathyroid adenomas and hyper-

plastic parathyroid glands in this series of patients was fre

quently identified, as documented by lower parathyroid/thyroid

activity ratios in the l ate phase images compared to the early

SUBTRACT ION

F IG UR E 7 . C o m pu te r s u b tr ac tio n e rro n e o us ly e x c lu d e d a 3 27 -m g p a ra th y

ro id a de no ma a pp are ntly b eca us e o f s up erim po se d a ctiv ity in a th yro id

a d e no m a in th e rig h t lo w e r lo b e o f th e th y ro id g la n d. (U p pe r le ft) T e c h n e tiu m -

9 9m -p e rte c hn e ta te im a g e, (u pp e r rig ht) e a rly T c-s e s ta m ib i im a g e, (lo we r

le ft) c om p ute r-s ub tra ctio n im a ge a nd (lo we r rig ht) la te T c-s e s ta m ib i

imag e .

phase images Table 3). Rapid washout also has been reported

by others 7,8). As a resul t, abnormal parathyroid glands could

be misinterpreted as thyroid nodules. Nodular foci with in

creased or separate sestamibi uptake relative to thyroid tissue on

ei ther the early or late images, or both, should be considered

abnormal ) .

r

M I E I

M I BI I M I N

SUBTRf tCTION

MIE I 3H

F IG UR E 6 . P a tie n t w it h fo u r h y p e rp la s t ic p a ra t h yr o id g la n d s 3 -g le ft u p p e r

g la nd , 1 .6 -g rig ht u pp e r g la nd , 1 .1 -g rig ht lo we r g la nd a nd 2 33 -m g le ft lo we r

g la nd ) a nd a c lin ic al h is to ry o f e n d s ta ge re n al d is e a se . O n ly th e la rg e s t (3 -g

le f t u p p e r g la n d ) w a s c le a rly id e n tifie d . ( Up p e r le f t) T e c h n e t iu m - 9 9m - p e rt e ch -

n e ta te im a g e , (u pp e r rig ht) e a rly T c-s e s ta m ib i im a g e, (lo w er le ft) c om p u t

e r-s u btra ctio n im a g e a nd (lo w er rig ht) la te T c-s e s ta m ib i im a g e.

SUBTRACTI ON

R GUR E 8 . Lo w er le ft ) C om p u te r-s u b tra c t io n im a g e, u p pe r le ft ) Tc -

p erte ch ne ta te im a ge a nd (u pp er rig ht) th e e arly T c-s e s ta m ib i im a ge d id

n ot in clu de a n e cto pie p ara th yro id a de no m a in th e fie ld o f v ie w . T he la rg er

fie ld o f v ie w T c-s e s ta m ib i im a g e o f th e n e ck a nd c he s t (lo we r rig ht) c le a rly

d e m on s tra te d th e e c to pie p ara th yro id a de n om a in th e m id lin e , u pp e r m e d i

a s t i num .

838

THE JOURNALOFNUCLEARMEDICINEol. 38 o. 6 une 1997

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Bernard et al. (7) hypothesized that the rapid washout of

99mTc-sestamibi may be related to a decreased number of

oxyphil cells, since their single case of a parathyroid adenom a

w ith rap id w ash ou t lacke d o xyp hil ce lls. H ow ev er, this h as b een

q uestio ned (9) an d req uire s fu rth er stu dy . O xy ph il cells u su ally

found in parathyroid adenom as are rich in m itochondria, and

m ito ch on dria c on te nt is th e h yp oth esiz ed m ec ha nism o f se sta -

m ib i reten tion in p arath yro id tissue (7 0).

L ate im aging, com puter subtraction and SP EC T im aging did

n ot sig nifican tly in crease th e sen sitiv ity or sp ecificity o f pa ra

thyroid im aging com pared to the visual subtraction of 99m Tc-

p ertech netate fro m early 9 9m Tc-sestam ib i im ages. T herefo re,

they may not be necessary on a routine basis. Computer

subtraction, late imaging and/or SPECT imaging may be

reserv ed fo r an y case w here abn orm al p ara th yro id tissu e c ann ot

b e id en tified o n in itial im age s.

Com puter subtraction, late im aging and SPECT im aging all

h ave p oten tial pitfalls b ut in in div id ual p atien ts m ay b e h elp fu l.

Com puter subtraction m ay highlight subtle areas of increased

99m Tc-sestam ibi uptake in sm all parathyroid nodules. L ate

im ag es d em on stratin g fo ci w ith retentio n o f 9 9m Tc-sestam ib i

m ay be attributed m ore confidently to abnorm al parathyroid

tissue. If the foci of increased sestamibi uptake have rapid

washout or washout at the sam e rate as norm al thyroid tissue,

then the foci have an interm ediate probability for being abnor

m al parathyroid tissue, and surgical exploration of these areas

may be helpful. SPECT helps to localize nodules in three

dimensions that m ay be helpful to surgical planning. SPECT

also can anatom ically separate parathyroid nodules from over

lapp in g thy ro id tissu e, ag ain in creasin g th e co nfiden ce th at th e

n od ules are ab no rm al p arath yroid tissu e.

A possible reason for why SPECT imaging had a lower

(79% ) sensitivity for detecting abnorm al parathyroid tissue in

th is serie s o f patien ts as op po sed to the 9 4% sensitivity rep orted

by Sfakianakis et al. (11) w as that they perform ed early SP EC T

im aging. In contrast, only late SP ECT im aging w as perform ed

in this study protocol for practical reasons. As a result of the

decreased count density of late SPECT images and higher

background im age noise, abnorm al foci w ere m ore difficult to

id en tify . A n a ltern ativ e to S PE CT im aging fo r p ractic es w ith ou t

a SPE CT cam era w ould be to acquire high counting rate oblique

im ages that decrease the overlap of thyroid and parathyroid

t is su es ( 8) .

Late imaging alone is not recommended. Two of the para

thyroid adenomas in the study group had rapid washout and

were not visible on late images. In addition, late images

occasionally had m ore overlapping activity in the neck strap

m uscles th at o bscu red foc i o f p arath yro id u ptake.

R ely in g o n co mpu ter-su btraction im ag es alo ne w ou ld also b e

a mistake. M isregistration of images (position and counts

norm alization) and patient m otion can m ake im age interpreta

tion difficult (12,13). M oreover, the sm aller field of view of

m any com puter subtraction protocols m ay m iss ectopie para

thyroid glands. So an im age with a field of view large enough

to include mediastinal ectopie foci should be in the image

p ro to co l (4 ).

Since an experienced surgeon will be able to localize up to

90% -95% of parathyroid adenom as during initial neck explo

ratio n, th e ro le o f p re op erative im aging b efore in itial su rge ries

has been questioned. H ow ever, failure to rem ove the abnorm al

parathyroid gland m ay result in significant patient m orbidity

6,14,15 . The potential of preoperative imaging is to decrease

operative tim e and decrease the chances for surgical failure,

such as locating small or ectopie parathyroid adenomas that

could be m issed during surgery.

L imiting surgeries to one side of the neck after a solitary

abnorm al gland has been localized by preoperative im aging is

not recom mended. Since only about 50% of the hyperplastic

p arath yro id glan ds w ere d ete cted b y scin tigrap hy , a p atien t w ith

m ultiple hyperplastic parathyroid glands could be m isinter

preted as having a solitary parathyroid adenoma and lead to

s urg ic al fa ilu re , sim ila r to th e e xp erie nc e o f S offe rm an e t a l. ( 6 ).

H ow ev er, im ag in g in c on ju nc tio n w ith q uic k a ss ay s o f in tra op er

ative parathyroid hormone levels and surgery lim ited to the

e xc is io n o f v is ib le p ara th yro id a de noma s h as p romis e (//).

P reo perativ e im ag ing w as clin ically u sefu l. Id en tify in g m e

d iastin al o r intrathy ro id al p arath yroid tissu e altered su rg ic al

planning. The former changed the usual cervical surgery to a

tran sm ediastina l ap proach , an d the latter alerte d th e su rg eon to

perform a thyroid lobectom y w hen an extrathyroidal parathy

roid nodule could not be located (16).

P ro ba bly th e mos t c ompe llin g re aso n to p erfo rm p re op era tiv e

im aging w as in patients w ho have failed prior surgery w here the

risk for ectopie parathyroid tissue is higher, up to 20% to 30%

14 . Small parathyroid glands and ectopie parathyroid adeno

mas that either recurred or were missed after initial surgery

were easily localized with imaging and excised for surgical

cu res in th is re po rt.

ON LUS ION

Late im aging, com puter subtraction and SPECT m ay not be

necessary since they provided only m arginal im provem ents on

v isu al co mp ariso n o f early sestam ib i a nd p ertech ne tate im ag es.

D oub le-p hase sestam ib i im ag ing w as less sen sitiv e, so b aselin e

thyroid im aging w ith 99m Tc-pertechnetate is recom mended.

P ara th yro id a de noma s in clu din g e cto pie p ara th yro id a de noma s

w ere easily identified, but only about half of the hyperplastic

p ara th yro id g la nd s w ere v isib le .

R F R N S

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PARAT HYRO IDMAGINGCOMPAR ISONh en e t a l. 8 39

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1997;38:834-839.J Nucl Med.

Charles C. Chen, Lawrence E. Holder, William A. Scovill, Ann M. Tehan and Donald S. GannSPECTSubtraction, Double-Phase Technetium-99m-Sestamibi and Technetium-99m-SestamibComparison of Parathyroid Imaging with Technetium-99m-Pertechnetate/Sestamibi

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