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OUR EXPERIENCE WITH TECHNETIUM 99 M SESTAMIBI SCINTIMAMMOGRAPHYIN EVALUATING BREAST LESIONS

K Shakthi Kumar*, Simran Singh*, Bg Ponnappa**, Tmr Panicker***,
C Rethinasabapathy***, A Govindan+, M Paul Korath++, K Jagadeesan+++
*Resident in Radiodiagnosis; **Registrar in Surgery; ***Medical Physicist; +Director, Dept. of Imaging; ++Chief Physician; +++Director; KJ Hospital Research and Postgraduate Centre, Chennai - 600 084.

INTRODUCTION

The need to distinguish between benign and malignant lesions is of prime importance both to the clinician and the patient. The investigations in common use have a high false positive rate which can be devastating or the patient. We have used sestamibi scintimammography in the evaluation of breast lesions. From our experience we find sestamibi scintimammography a reliable test which may be used to clearly differentiate between benign and malignant lesions. We present our experience with this compound.

MATERIAL AND METHODS

Procedure 1

Scintimammography was performed using a ELSCINT gamma camera with single photon emission computed tomography (SPECT) equipped with a medium resolution and medium sensitivity collimator. The spectrometer was set at 140 KeV with a 10% window. Each patient received an intravenous injection of 20 millicurie technetium 99 m sestamibi in the arm contralateral to the breast with the abnormality. Five minutes after injection, a ten minute lateral image of the breast with the suspected lesion was taken in the prone position with a lead shield between the two breasts. The patient was repositioned with the contralateral breast dependent and a lateral image was acquired. If the lesion was seen near the chest wall, a 30 degree posterior oblique view was taken. The lateral images were repeated after one hour. A ten minute anterior chest image with the patient’s arms raised was taken to visualise the axilla. [1]

Scintimammography was positive for carcinoma if there was any area of increased focal uptake in the involved breast and was negative if there was diffuse unilateral or bilateral uptake or no uptake. This was compared with the final tissue diagnosis obtained by histopathology or cytology.

Eight cases with breast lesions were studied. Scintimammography was performed and this was later compared with histopathology/cytology. Of these eight cases five were reported as carcinoma, two were fibroadenoma and one was fibroadenosis. The carcinoma and fibroadenoma were proven by histopathology and the fibroadenosis by cytology.

The scintimammography showed uptake in all the five cases which were later proved to be malignant. There was no area of focal uptake in the cases which were later proved to be benign. We report 100 per cent true positives and true negatives and no false positives or negatives. Though the number of patients studied is relatively small the 100% sensitivity and specificity compares well with the 72-100% [9-13] reported for technetium 99 m sestamibi in the detection of carcinoma breast. This test was also found to be a reliable means of assessing spread to the contralateral breast and distant metastases.

DISCUSSION

Evaluation of breast lesions is of great importance not only because they are a common clinical problem but also since a wrong diagnosis can cause great physical and psychological hardship for the patient. Mammography has a positive predictive value of only 15-30% for non palpable malignancy [2] and positive predictive value of only 22% for palpable carcinoma. [3]

Technetium 99 m sestamibi is a lipophilic Tc 99 m organometallic complex. Initially used for cardiac imaging, the first use of Tc 99 m sestamibi in tumour imaging was reported by Muller et al [4] in 1987. It has since been used in the assessment of patients with recurrent brain gliomas, bone tumours and carcinoma of the thyroid gland. [5-7] It has been found to be highly sensitive in the detection of breast carcinoma. [1]

When an intravenous injection of technetium 99 m is given it is seen to concentrate in the heart, liver, intestines and in the malignant breast tissue. The concentration in the carcinoma breast tissue overlaps the activity in the heart and the liver, hence special views are required. Plastic overlay has been used but prone position with imaging of the dependent breast, gives maximum separation of breast tissue from myocardium and liver. [8]

CONCLUSION

Scintimammography with technetium 99 m sestamibi using the above protocol has a low whole body radiation dose of 0.3 rad and the breast receives minimal radiation. [1] The high specificity, sensitivity and positive predictive value make it an ideal tool in the evaluation of breast lesions.

REFERENCES

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