Percentage arterial enhancement: an objective index for accurate identification of parathyroid adenoma/hyperplasia in primary hyperparathyroidism

Abstract

Background

Radiation exposure to neck by 4DCT is relatively high and limits its use as a first line investigation in evaluation of PHPT. Radiation exposure can be reduced by restricting the number of CT phases. Our aim was to study the performance of 4DCT in cohort of surgery-naïve primary hyperparathyroidism(PHPT) patients, and to evaluate percentage enhancement as an objective radiological index to discriminate parathyroid lesions(adenoma/hyperplasia) from thyroid tissue and lymph nodes.

Materials and method

Retrospective study of 49 PHPT patients {(44 Single gland diseases(SGD) and 5 multiple gland disease(MGD)} who underwent 4DCT (unenhanced, early arterial, early venous and delayed venous phase) pre-operatively. Two radiologists who were blinded to surgical location of parathyroid lesions examined the scans. Attenuation values were recorded for parathyroid lesions(n=50), thyroid gland(n=50) and lymph nodes(n=12) in different phases. Percentage enhancement for different phases was calculated as "(HU in a specific enhanced phase–HU in unenhanced phase)/HU in unenhanced phase" X100.

Results

Interrater reliability between the two radiologists was 0.83(Cohen's kappa). In SGD, sensitivity and PPV was 93.18% and 98.8% for lateralization, and 89.77% and 95.18% for quadrant localization respectively. In MGD, 4DCT showed 50% sensitivity and 100% PPV. Percentage arterial enhancement showed highest area under curve(AUC=0.992) for differentiation of parathyroid lesions from thyroid tissue and lymph nodes. A cut off value of 128.9% showed 95.8% sensitivity and 100% specificity for the identification of parathyroid lesions.

Conclusions

We propose that percentage arterial enhancement can be used as an objective radiological index for accurate identification of parathyroid adenoma/hyperplasia.

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