Uncommon pelvic mass: GIST mimicking adnexal tumour

Clinical History

A 66-year-old woman was referred to our institute to define a sonographic finding of a pelvic mass.
She presented with a history of pelvic pain, asthenia and weight loss. Gynaecological examination: Upper deflection of the cervix by a compressive lesion in the posterior cul-de-sac. CA125= normal.

Imaging Findings

The patient underwent a pelvic MR that showed a large, lobulated tumour localized in the pouch of Douglas, measuring 15, 4x10, 6x11, 7cm.
It did not invade the uterus or the sigmoid colon and it was in close relation with the intestinal loops. The ovaries were not visualized.
The mass was heterogeneous, with focal areas of hypointensity on T1W1 showing high-signal on T2WI, and avid gadolinium uptake on fat-suppressed T1W1. These areas also demonstrated restricted diffusion, suggesting solid malignant nature. Other areas showing intermediate signal on T1W1 were hyperintense on T2WI and did not enhance, which suggests haemorrhagic and necrotic nature.
The patient underwent a small bowel and rectal partial resection with total hysterectomy and bilateral anexectomy. The resected specimen contained, in a paraintestinal location, a 12cm partially cystic and necrotic nodular tumour.
The histopathologic diagnosis was small bowel malignant GIST.

Discussion

Gastrointestinal stromal tumours (GISTs) are mesenchymal tumours which account for less than 1% of all gastrointestinal tumours [1, 2]. They can occur throughout the GI tract, mesentery, omentum and retroperitonuem, with 20-30% arising in the small bowel [3, 4].
They range from benign tumours to aggressive tumours (10-30%) [3].
The majority of GISTs presents at ages above 40 years. Gastrointestinal haemorrhage due to mucosal ulceration is a frequent symptom. Abdominal pain, vomiting, weight loss and intestinal obstruction can also occur [4].
Extraluminal and eccentric growth is frequently encountered in malignant small intestine GISTs, which can encase non contiguous segments [2, 4].
The solid component of GISTs is typically hypointense on T1WI and shows intermediate/high signal intensity on T2WI, enhancing avidly following the administration of gadolinium. Signal intensity of focal haemorrhagic areas varies according to the age of haemorrhage [1, 2, 5].
Small bowel GIST’s 5-year survival rate is 40-50% [1].
Female pelvic masses commonly arise from reproductive organs, however, non gynaecological lesions originating from urinary and gastrointestinal systems, from the peritoneum, retroperitoneum and from adjacent soft tissues are important pitfalls that radiologists and gynaecologists must take into account [1].
Identification of the location of the mass (intra or extraperitoneal) is based on anatomic landmarks and should also take into account the patient’s age, clinical and gynaecological history [1].
MRI is the modality of choice to evaluate US and CT indeterminate pelvic masses and has capability to differentiate benign from malignant lesions [1, 6].
In our case MR was performed to characterize an indeterminate adnexal mass that revealed to be of gastrointestinal origin.
Despite being an uncommon pelvic mass, GISTs must be considered in the differential diagnosis of large adnexal masses, since they may have similar imaging characteristics to ovarian cancer and their therapy and prognosis are very different.

Differential Diagnosis List

Final Diagnosis

Small bowel malignant GIST

URL:	https://www.eurorad.org/case/11325
DOI:	10.1594/EURORAD/CASE.11325
ISSN:	1563-4086