MIBI scintigraphy in hypofunctioning thyroid nodules--can it predict the dignity of the lesion?

Several authors have investigated the value of technetium-MIBI scanning to predict the dignity of hypofunctioning, cold thyroid nodules (HTN) in regions with differing levels of iodine supply. They concluded that an MIBI scan can exclude thyroid malignancy, although comparisons between the studies are of limited value owing to differences in methodology and wide variations in patient selection criteria. The present study investigates whether the above claim is also valid in Germany, a country with a long-standing and persistent, mild iodine deficiency and a high incidence of nodules in large goiters with a low prevalence of malignancy.

The study compares the results of 99mTc-MIBI scintigraphy (incl. SPECT and planar images) in HTN (MIBI) with those of fine-needle aspiration biopsy (FNAB) and histology. Of 154 consecutive patients (121 women, 33 men; mean age 56 +/- 12 years), 73 underwent thyroid surgery from which the results of FNAB and MIBI were assessed. Selection criteria were risk estimation or conditions limiting the feasibility of FNAB. The mean thyroid volume was 42 +/- 25 ml, with 2.1 +/- 1.4 nodules per patient.

Histology revealed thyroid malignancies in 8 out of 73 patients (11.0%). The negative predictive value for MIBI was 97%, which is comparable to FNAB (94%). However, in 19.5% of patients FNAB was indeterminate. Lower specificity (54%) and low positive predictive value (19%) showed that MIBI accumulation cannot differentiate between malignant and benign thyroid nodules. However, comparison with cytological and/or histological findings indicated that it could distinguish between lesions with differing rates of mitochondrial metabolism.

Even in areas of former or mild iodine deficiency MIBI forms a basis for choosing between wait-and-see and surgical strategies if FNAB is unfeasible or not representative. However, even for pathological MIBI results, the prevalence of malignancy is not very high.