Clinical History
A middle-aged, perimenopausal G3 female presented with unremarkable past medical history apart from previous diagnosis of uterine leiomyoma (years earlier). Currently the patient is not complaining of pelvic or gynaecologic symptoms, with low-grade anaemia as the only laboratory abnormality.
Imaging Findings
At the most recent gynaecologic visit, increased uterine leiomyoma (compared to its previously reported size) was discovered, therefore the patient was referred to our hospital to undergo MRI before surgery.
MRI (Figs.1, 2) confirmed the presence of a solitary 5.5-cm roundish subserosal mass deforming the uterus along its entire length, consistent with a type 6 lesion (less than 50% intramural) according to the International Federation of Gynecology and Obstetrics (FIGO) leiomyoma subclassification system. Compared to the usual myoma appearance, the lesion showed atypical signal features including T1-isointense and moderately T2-hyperintense signal in respect to the outer myometrium, mild heterogeneity without necrosis or haemorrhagic changes, moderately high diffusion-weighted signal with corresponding apparent diffusion coefficient (ADC) value 1.5x10-3 mm2/s, strong contrast enhancement without nonenhancing regions.
After hysterectomy, surgical pathology diagnosed hypercellular uterine leiomyoma without signs of dysplasia or neoplasia.
Discussion
Also known as myomas or fibroids, leiomyomas by far represent the commonest uterine neoplasm and are encountered in up to 75% premenopausal females. Often multiple, leiomyomas are benign stromal tumours of the myometrium composed of uniform smooth muscle cells with varying amounts of intervening fibrous connective tissue. Their size ranges from millimetres to huge masses, and varies under hormonal influence with growth during pregnancy and on oral contraceptives, frequent regression after menopause. Often asymptomatic, leiomyomas may cause infertility, dysmenorrhoea, menorrhagia, pelvic pain or organ compression [1, 2].
Albeit leiomyomas are generally detected by transabdominal and endovaginal ultrasound, MRI is highly accurate and increasingly used to detect, measure and categorise leiomyomas as submucosal, intramural or subserosal before therapeutic choice between myomectomy (open, laparoscopic or hysteroscopic), hysterectomy, GnRH-analog therapy and arterial embolization. Typically, MRI depicts leiomyomas as well-circumscribed lesions with homogeneous T2-hypointensity compared with the outer myometrium and minimal contrast enhancement [2, 3].
Occasionally, atypical features such ad oedema, cystic or hyaline degeneration, and variant subtypes (accounting for 1%) of leiomyomas result in increased T2-weighted signal intensity and therefore pose a diagnostic challenge. Among the latter, hypercellular leiomyomas (HCL) are characterised pathologically by softer consistence, compact structure with increased cellularity compared to surrounding myometrium, little or no collagen, abundant blood vessels, absence of nuclear atypia and mitotic activity. Patients with HCL are more likely to be symptomatic with menometrorrhagia, and are cured with hysterectomy. As this case exemplifies, compared to ordinary and degenerated leiomyomas HCL usually appear as solitary, fairly large masses with intermediate-to-high T2 signal intensity and avid homogeneous enhancement [2-6].
Particularly in large or growing lesions, the key differential diagnosis is the rare uterine leiomyosarcoma (ULMS) which generally occurs after menopause and appears as large, poorly demarcated masses with necrosis, haemorrhagic changes and heterogeneous enhancement with central nonenhancing areas. Assessment of malignancy risk requires careful combination of multiparametric information including morphologic features, unenhanced signal, diffusion-weighted imaging (DWI) and contrast enhancement. Whereas ordinary leiomyomas show “blackout” hypointensity on both DWI images and apparent diffusion coefficient (ADC) maps, ULMS show restricted water diffusion because of increased cellular density and altered cellular membranes, significantly lower ADC values compared to the normal myometrium and degenerated leiomyomas. However, diagnosis of ULMS is difficult and often established pathologically since imaging features such as rapid growth, irregular margins and heterogeneity are fairly unspecific. Furthermore, due to their histologic pattern HCL show DWI appearance and ADC values overlapping with those of ULMS [3-7].
Differential Diagnosis List
Large subserosal hypercellular leiomyoma of the uterus.
Oedematous leiomyoma
Leiomyoma with hyaline (collagen) degeneration
Leiomyosarcoma
Final Diagnosis
Large subserosal hypercellular leiomyoma of the uterus.
