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Letters to the Editor |
Department of Radiology and Nuclear Medicine, Royal Free Hospital, Pond St, London NW3 2QG, England, e-mail: eloney@demios.com
Editor:
We read with interest the article by Dr De Feo and colleagues in the February 2000 issue of Radiology (1) in which they suggested that the combination of ultrasonography (US) and technetium 99m 2-methoxyisobutyl-isonitrile (MIBI) scintigraphy should be used in the localization of parathyroid nodules, with scintigraphy as the first-line investigation followed by in all cases with US.
Currently at our institution, we use US and dual-phase 99mTc MIBI single photon emission computed tomography (SPECT) to locate and identify abnormal parathyroid masses (2). Recently, we reviewed our experience with the two modalities during the past 4 years.
The SPECT studies were performed 15 minutes and 4 hours after the injection of 740 MBq of 99mTc MIBI. The presence of an adenoma was based on persistent focal areas of tracer accumulation. High-spacial-resolution (7.5–10-MHz) US was performed, and enlarged parathyroids were identified as hypoechoic masses with color and power Doppler US, which increased their conspicuity.
A total of 59 patients underwent both tests. There was 71% (42 patients) concordance; 17 patients had concordant positive findings, and 25 had concordant negative findings. Of the 17 discordant results, 11 were positive at 99mTc MIBI SPECT and negative at US, and six were positive at US and negative at 99mTc MIBI SPECT. Thirteen patients with concordant positive findings have undergone surgery, and all patients were proved to have adenomas. Three patients with discordant findings also underwent surgery. Two patients (with positive 99mTc MIBI SPECT findings and negative US findings) had an adenoma, and one patient (with negative 99mTc MIBI SPECT findings and positive US findings) had only glandular hyperplasia.
These results demonstrate the sensitivity of 100% with 99mTc MIBI SPECT so far and reinforce its role in the depiction of parathyroid adenomas. We recommend that US is necessary in only those patients who have negative 99mTc MIBI SPECT findings; even then, its role in depicting extra adenomas has yet to be demonstrated in our study.
REFERENCES
Department of Clinical Physiopathology, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy, e-mail: m.brandi@dfc.unifi.it
We read with interest the letter from Dr Loney and colleagues with the comments on our article (1) and on their recently published article (2). We disagree, however, with their recommendations on the basis of the following considerations.
First, the aim of our study was to optimize the methods for the localization of pathologic parathyroid tissue (either adenomatous or hyperplastic) with regard to the characteristics of primary hyperparathyroidism, that is, the frequent occurrence of small nodules and associated diffuse or nodular thyroid disease that could potentially interfere with magnetic resonance (MR) imaging, US, and scintigraphic techniques. We obtained surgical and histopathologic documentation of the location, size, and pathologic characteristics of each nodule, as evidenced with all the techniques used; all the patients underwent the three examinations in our prospectic study. According to our data, the combination of 99mTc MIBI scintigraphy and US leads to a useful enhancement of sensitivity and specificity in parathyroid imaging, since both techniques appear to be complementary.
Second, 99mTc MIBI SPECT was not available at the time our study was performed. We have been using this technique for the past 2 years; preliminary data on 15 patients with primary hyperparathyroidism and who underwent surgery indeed suggest a slight increase in sensitivity with respect to the planar technique. However, even 99mTc MIBI SPECT appears to have the same pitfalls that we observed with the planar technique, that is, the possibility of both false-positive results (such as a case of a Hürthle cell adenoma and a sarcoid lymph node with clinical features mimicking a primary hyperparathyroidism) and false-negative results (in cases of nodules with major axes shorter than 1 cm with low metabolic activity or partial necrosis).
Third, a comparison between the scintigraphic and US results in our study and the authors’ studies (see letter by Dr Loney and colleagues and reference 2) cannot be performed. In fact, we obtained the surgical and histopathologic reports of all patients included in our study. On the contrary, only 16 of 59 patients (see letter by Dr Loney and colleagues) and 13 of 69 patients (2) underwent surgery; only 37 of the 69 patients had positive MIBI imaging findings. The authors do not indicate the dimensions of pathologic glands (all of which are reported to be adenomas [bigger in size with respect to hyperplastic glands] that were, on the contrary, well represented in our study), and they do not indicate the frequency of the associated thyroid disease.
Indeed, our study was aimed at obtaining information in patients with discordant scintigraphic and US results. According to our findings, US adds useful information either in cases with positive scintigraphic results or in cases with negative 99mTc MIBI SPECT results. Preliminary data on the application of the protocol proposed on the basis of our prospective study findings (neck US following the indications of 99mTc MIBI scintigraphy) in 30 patients show an additional increase in sensitivity and, in particular, in specificity with the combination of the two techniques with respect to both our previous study findings and to the introduction of 99mTc MIBI SPECT scintigraphy.
REFERENCES
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