Uterine leiomyomas are best diagnosed, assessed, and monitored by US. Pelvic MRI is needed when the fibroid is symptomatic and needs management since it's the most accurate modality in characterizing the lesions. Submucosal ones can also be assessed by hysteroscopy. The main benefit of hysterosalpingography (HSG) in fibroids is as a preoperative assessment of the uterine cavity and the site and size of submucosal fibroids. It also helps assess any concomitant tubal affection especially if the patient seeks fertility (like this patient). 

Post-myomectomy HSG may also show any residual fibroid or complications of the surgery such as synechiae.