At our institution, CESM has been in clinical use since August 2019 and we have analysed 50 cases in this preliminary study, based on the indications given (fig 1).
Studies have shown the low energy images of CESM to be non inferior to conventional mammogram images despite the presence of intravenous iodinated contrast and low energy CESM images may be used for interpretation in place of the FFDM[1,2]. Hence, we used the xray mammographic lexicon and template for interpreting the low energy images.
Regarding the second group of subtracted images in CESM, enhancement was seen in most malignant and some benign lesions picked up in our study. Thus, we found that contrast enhancement alone is not enough to diagnose malignancy, and the enhancement patterns need to be categorised further. Few studies have used MRI lexicon to interpret and report the subtracted images of CESM [3,4].
Hence, we formulated a structured reporting format for CESM which incorporated the mammogram and MRI BIRADS lexicons ( Table 1) and we followed it in all our cases.
CESM is performed in our institution as follows
–With the breast out of compression, nonionic low-osmolar iodinated contrast material (Iodixanol, 320 mg I/mL; Visipaque, GE Healthcare) is injected IV using a power injector at a standard dose of 1.5 mL/kg at a rate of 3 mL/s (Medrad Salient Dual CI system , Imaxeon).
–Two minutes after the start of the injection, the breast is placed into compression (side of interest first) and paired low-energy (23–32 kVp) and high-energy (45–49 kVp) images are obtained in standard craniocaudal and mediolateral oblique views (Selenia Dimensions Mammography System, Hologic).( fig 2)
Few illustrative cases are discussed below as per the indications and all the findings are described as per the lexicon.
CESM to identify potential undetected malignancies (fig 3)
CESM to evaluate extent of disease preoperatively (fig 4)
CESM as a problem solving tool (fig 5)
CESM as an alternative to MRI for high risk screening in claustrophobic patient (fig 5 B)
ENHANCEMENT PATTERNS
All the the background parenchymal enhancements in our study were symmetric and could be graded as minimal, mild or moderate. (fig 6). A marked BPE was not seen in any of our cases.
We found that the enhancement patterns in CESM could be categorised as mass and non mass enhancement. We couldn't correlate the third enhancement pattern given in MRI lexicon i.e. focus to any of the patterns obtained in our study.
TYPICAL ENHANCMENT PATTERNS
Among the enhancing masses, those with irregular shape, spiculated margins and heterogenous enahancement were malignant (fig 7) as proved from HPE.
Those with round/oval shape, circumscribed margins and homogenous enhancement were mostly benign, either on HPE or on ultrasound. Fibroadnenomas had an oval shape & thethere was non-enhancing septations within them. (fig 8)
DISCORDANT PATTERNS
A lesion showed patterns that could be benign and malignant, like a round heterogenously enhancing mass ( fig 9). HPE was done for confirmation which showed the lesion to be benign. However, considering the history of the patient, she was called back for a wide local excision after wire localisation and it was proved to be a carcinoma.
Another confusing case was that of an abscess which showed enhancement that could be described as rim enhancement or clustered rings. Ultrasound confirmed the final diagnosis of abscess ( fig 10).
CALCIFICATIONS
Ability to evaluate abnormal calcifications is an advantage of CESM over MRI. The morphology of calcifications can be assessed in low energy images while the subtracted images show calcifications as dark specks. CESM was used for evaluation of suspicious calcifications (seen in 3D Mammogram) in 4 patients in our study, 1 of which was associated with non mass enhancement in subtracted image and later proved malignant (fig 11) and one had an underlying malignant lesion (fig 3 B). Rest of the cases had no positive findings. However, CESM gave us the confidence to advise routine follow up to these patients.
FOCAL ASYMMETRY AND ARCHITECTURAL DISTORTION
Similarly, for suspicious findings like focal asymmetry and architectural distortion, CESM served as a problem solving tool, whenever MRI was not possible due to cost constraints or claustrophobia. Targetted ultrasound in these patients was negative, but these patients are kept on interval follow up as biopsy was not done.
EVALUATION OF CYSTIC LESIONS
Simple cysts didn't show any enhancement in most of our cases. However, there was a large simple cyst that showed rim enhancement in CESM identical to the pattern seen in MRI. (fig 12). Another case was that of a complex cyst that showed enhancement of the solid component and later proved to be complex papillary lesion wiuth atypia. (fig 13).