Endometriosis and its rare complication, malignant transformation

A 41-year-old female came to the gynaecology outpatient department with a history of painful menstruation, lower abdomen pain, dyspareunia and secondary infertility. There was no history of fever, vaginal discharge, recent surgery or previous obstetric surgery. Pelvic examination revealed cervical motion tenderness with no abnormality in external genital organs or perineum.

A transvaginal ultrasound revealed focal adenomyosis, a simple right ovary cyst and a complex cyst in the left adnexa.

Contrast-enhanced MRl confirmed a well-defined, oblong-shaped, multi-loculated cystic lesion in the left adnexa, having T1FS hyperintense signals (Figure 1a) and heterointense signals on T2W images with fluid-fluid level (T2 shading) (Figures 1b and 1c). The left ovary was not visualised separately. A heterogeneously enhancing, eccentric nodule having T1 isointense and T2 intermediate signal intensity (Figures 2a, 2b, 2c, and 2d) with hyperintense signal on DWI and hypointense signal on corresponding ADC maps was also seen in the lesion (Figures 3a and 3b). The possibility of a malignant transformation in tubo-ovarian endometriosis was suggested. Ultrasound findings indicating focal adenomyosis and a simple right ovary cyst were also confirmed on MRI.

The patient was operated, and the histopathological examination confirmed low-grade endometrioid adenocarcinoma (malignant transformation) in left tubo-ovarian endometriosis (Figure 4a). Secondary carcinomatous deposits in lymph nodes were also seen (Figure 4b).

Endometriosis is a common, chronic condition, which is prevalent in 5%–15% of reproductive age females. It is characterised by the presence of endometrial glands and stroma at ectopic location [1]. While endometriosis can affect any organ, common sites include ovaries, fallopian tubes and other pelvic organs/ligaments. Multiple theories are proposed to explain the pathophysiology, but none of them is established.

The clinical symptoms and severity of the disease depend on the site of ectopic tissue rather than the disease load. Usual complaints are chronic pelvic pain, dysmenorrhea, dyspareunia and infertility [2].

Ultrasound findings of typical endometriosis include well-defined cystic lesions with homogeneous low-level echoes [3]. Even though the malignant transformation is rare according to literature (less than 1%), endometrioma should be carefully evaluated to rule out any malignant focus/nodule [4]. Some of the mimickers also need to be ruled out, like intra-cystic clots, which may appear like mural nodules despite clots not showing internal vascularity [5]. Also, cyclic hormone-related changes in ectopic endometrium should not be confused with malignant transformations [5].

On MRI, typical endometriosis shows T2 shading and absence of internal enhancement on post-contrast images. The malignant changes in endometriosis are suggested by the presence of enhancing solid nodules/components, diffusion restriction on DWI and ADC maps in solid nodules, and unusual increase in size, or disappearance, of T2 shading [6].

The histological criteria for diagnosing endometriosis-associated malignancies (EAMs) include the presence of endometriosis tissue near the site of the tumour, the tumour having endometrial tissue, exclusion of metastasis, and a histological transition from benign to malignant change [7]. Ovaries are the site of approximately 80% of EAMs, while one-fifth of the malignancies are extra-ovarian [7]. Histological subtypes of malignant ovarian endometrioma include endometrioid (the most common), clear cell, mucinous, low-grade serous and high-grade serous carcinomas. Most of the tumours are histologically low-grade. Extra ovarian malignancies associated with endometriosis are commonly endometrioid or clear cell carcinomas and rarely include endometrial stromal sarcomas, adenosarcomas, and carcinosarcomas.

Surgical excision is the mainstay of treatment in malignant endometriosis.

Take Home Message / Teaching Points

• Even though the malignant transformation of endometrioma is rare, radiologists should always look for the features which may suggest malignant transformation.
• Malignant transformation can be differentiated from benign endometriosis, as benign endometriosis will not show enhancing and restricting solid nodules.
• Haemorrhagic cysts are usually T1 hyperintense with absence of typical T2 shading or enhancing solid components.
• A patient with a tubo-ovarian abscess will have a fever with a cystic lesion showing internal diffusion restriction on MRI and absence of internal enhancement.

Written informed consent was obtained and the identity of the patient is kept confidential throughout the manuscript and related documents.