An Online Calculator for Estimating Breast Implant Volume from Imaging (2024)

Summary:

Breast implant surgery remains one of the most common surgical procedures performed in the United States. Implant exchange can be complicated by unavailability of medical records or implant identification cards. Using chest imaging of 154 breast implants, an algorithm for estimating breast implant volume was generated. Based on four simple measurements and patient body mass index, a free, online calculator was created with a mean error of volume estimate of less than 1 cm³ and a SD of 44 cm³. In instances where a surgeon does not have implant records available but has chest imaging, this online tool can be used to obtain a relatively accurate estimate of implant volume.

INTRODUCTION

Breast implant placement remains one of the most common procedures performed by plastic surgeons in the United States.¹ Lifetime revision and implant exchange rates remain high. In the setting of breast reconstruction, implant revision rates have been found to be as high as 35.5%.^2,3 The most common reasons for implant exchange are capsular contracture and patient requested size changes, followed by leakage, rupture, infection, and rippling.³ However, as patients change surgeons or lose their implant identification cards, accurately identifying the existing implant size or type can be challenging. Even at the same practice, medical records may only be maintained for a period of 5–10 years depending on state law.⁴ Although increasing use of electronic medical records may improve record keeping, systems are inconsistent across hospitals, and many private practices continue to rely on paper records. In cases where implant identification is not possible, surgeons must approximate the implant volume and select implants for the operating room with limited information.

Previous literature has examined whether magnetic resonance imaging (MRI) can be used to ascertain implant volumes.^5–7 Although the FDA recommends routine breast ultrasounds or MRI scans for patients with implants,⁸ only 5% of patients ever receive a breast MRI.³ Chest computed tomography (CT) imaging is less expensive, more readily available, and although not formally recommended by guidelines, frequently implemented for cancer staging or surveillance.^9,10 Our study validated an algorithm created to estimate implant volume using simple measurements from a chest CT scan and introduces a free, interactive, online tool for volume estimation.

MATERIALS AND METHODS

RESULTS

The records of 947 patients who underwent implant-based reconstruction following mastectomy were reviewed, of which 95 (10.0%) had an existing chest CT scan and implant catalog number recorded. Two patients with anatomic implants and three patients with only axial view CT scans were excluded. Of the 90 patients included in the final analysis, 26 (28.9%) had unilateral implants, whereas 64 (71.1%) had bilateral implants. In all, 154 breast implants were included in the analysis. Mean BMI was 26.52 kg/m², and mean implant volume was 531.07 cm³ with an SD of 164.31 cm³. All three US manufacturers were represented, with primarily Mentor (87.0%) implants followed by Allergan (11.0%) and Sientra (2.0%) (Table 1).

Five variables—axial diameter (mm), axial projection (mm), sagittal diameter (mm), sagittal projection (mm), and BMI (kg/m²)—were included in the model for estimating breast implant volume. The equation

$$\begin{array}{l}\text{Volume}\left({\text{cm}}^{\text{3}}\right)=-873.3+\left(3.9\times \text{Axialdiameter}\right)+\left(4.0\times \text{Axialprojection}\right)+\\ \left(3.0\times \text{Sagittaldiameter}\right)+\left(2.3\times \text{Sagittalprojection}\right)+\left(4.8\times \text{BMI}\right)\end{array}$$

related CT diameters/projections and BMI to estimated implant volumes (cm³). The model was calibrated to accurately predict breast implant volume. The algorithm-derived breast implant volumes fell within a normal distribution with a mean error of 0.6 cm³ and median error of 8.0 cm³. The SD of error was 43.6 cm³ and correlated well with manufacturer-specified volumes (adjusted r² = 0.9214). A breast implant size estimator using this algorithm was created on the website domain https://breastimplantcalculator.com/ as an interactive free tool (Fig. 2).

DISCUSSION

We present an accessible online calculator for estimating breast implant size from chest imaging. With four linear measurements from a chest CT scan, an estimated volume with an error distribution can be calculated. Breast implant revision surgery is complicated by unavailable implant identification cards or operative records requiring surgeons to approximate implant size from physical examination. Improved preoperative estimates of implant size can streamline implant ordering and provide improved surgical preparation.

A recent study by Levine and Kassira described highly accurate volume estimation using MRI imaging through the use of downloadable software,⁵ and in cases where exact volume estimation and detailed anatomical survey is needed, an MRI scan may be necessary. In contrast, our website https://breastimplantcalculator.com/ offers measurements that can be extrapolated from electronic medical records directly without the need for additional software and through the utilization of CT scans. The algorithm allows for accuracy with a mean error of less than 1 cm³ and 68% of estimates falling within 44 cm³ of the true volume. Further research will explore whether an algorithm can be validated for use with chest x-ray.

Given the risk of radiation, this calculator is most useful for patients with existing prior chest CT scans and unavailable implant records.¹³ Limitations of our study include that the primary indication for these implants was breast reconstruction, rather than breast augmentation, and that the majority of implants were from one manufacturer. Finally, although our study included a range of implant sizes, it may not be applicable to anatomic teardrop-shaped implants.

CONCLUSION

For patients whose breast implant size is unknown and who have a chest CT scan available, we offer an accessible online calculator (https://breastimplantcalculator.com/) to estimate implant volume with high accuracy.

Footnotes

REFERENCES