Uterine lipoma: an incidental finding in a patient with retrocaecal appendicitis

Clinical History

A female patient presented to the Emergency Department with abdominal pain of acute onset. The pain was located on the right inguinal area. Laboratory examinations revealed leukocytosis.

Imaging Findings

The patient was initially referred for abdominal ultrasound, which could not locate the appendix due to the presence of gas inside the ascending colon. However, ultrasound of the lower abdomen identified a relatively well-circumscribed and homogeneously hyperechoic lesion within the uterus. Colour Doppler technique characterized the mass as avascular. (Fig. 1) The patient was further evaluated with CT. This examination revealed the presence of a retrocaecal appendix with distended lumen and thickened and enhancing wall. There was also periappendiceal fat stranding and thickening of the lateroconal fascia. (Fig. 2) Inside the uterus, there was a well-defined rounded mass of fat attenuation (-64 HU) measuring 2.6x3 cm. This mass showed no enhancement after the intravenous administration of contrast medium. (Fig. 3) The overall imaging appearances of this lesion are in keeping with a benign uterine lipoma.

Discussion

The uterus represents a very rare location for lipomas which are frequent benign tumours consisting of adipose tissue. Uterine lipomas (UL) have a reported incidence of 0.03-0.2% with a limited number of cases reported in the literature. [1] Pure lipomas of the uterus are part of the broader group of mesodermal uterine fatty tumours (UFT). The latter include benign tumours made of adipose cells, connective tissue or smooth muscle cells in varying proportions. Depending on the exact content of the tumour, pure lipomas, lipoleiomyomas and lipofibromas occur. [1, 2]
UL may be solitary or multiple and affect postmenopausal women aged more than 50 years who usually present with symptoms like vaginal bleeding, pelvic discomfort, pain, urinary frequency or constipation. [1, 3, 4] Thanks to their benign nature and excellent prognosis, surgical resection is only indicated if there are symptoms. Moreover, malignant conversion of UL is rare and thus follow-up is not considered necessary. [1, 5]
Imaging permits accurate diagnosis of UL and thus prevents unnecessary surgery. UL may vary in size and are situated usually in the corpus of the uterus. The majority of UL are intramural, whereas a smaller percentage submucosal or subserosal. [1, 2, 4] Imaging characteristics depend on the histology of UL. As a result, ultrasound identifies them as well-defined hyperechoic and avascular lesions. A hypoechoic rim at the periphery of the mass can be present and created by a layer of smooth muscle cells. UL appear on CT as heterogeneous or homogeneous lesions with fat attenuation (-40 to -100 HU) and no enhancement. [1, 2] Depending on the tumour’s histology, internal septa or solid parts may appear on CT. [3, 6] MRI is an excellent imaging modality thanks to the detailed images it provides and non-ionising nature. UL appear with high signal intensity in both T1 and T2 weighted sequences and demonstrate low signal on fat suppression images. The presence of chemical shift artefact on out of phase images confirms the presence of adipose tissue and establishes the diagnosis of UL. The fibrous pseudocapsule of UL can be detected with MRI as a peripheral low signal intensity rim. [3] MRI is superior to CT in differentiating UL from adnexal masses and demonstrating their internal structure by identifying enhancing septations within the tumour. [1, 3] The diagnosis of a fatty uterine tumour becomes more difficult in cases of exophytic or pedunculated masses. [4] In conclusion, accurate imaging identification of fat content and uterine location of a mass establishes the diagnosis of a UL.

Differential Diagnosis List

Final Diagnosis

Uterine lipoma incidentally found in a patient with retrocaecal appendicitis

URL:	https://www.eurorad.org/case/12803
DOI:	10.1594/EURORAD/CASE.12803
ISSN:	1563-4086