Pelvic Lipomatosis: a case report with classic imaging findings

A 51-year-old male patient with no comorbidities presented with lower abdominal swelling and burning micturition. On examination, a mass was felt in the hypogastric region with side-to-side mobility.

Ultrasound of the abdomen and pelvis showed bilateral hydroureteronephrosis, with abnormal morphology of the urinary bladder; the cause of obstruction, however, could not be determined. A subsequently performed intravenous pyelography (IVP) also showed bilateral hydronephrosis with proximal hydro ureter (Fig. 1a). The prone delayed IVP image revealed an “inverted tear-drop/ pear-shaped” urinary bladder with dilated distal ureters (Fig. 1b). CT scan of the pelvis was performed to rule out a space-occupying lesion as the cause of bladder outlet obstruction, which revealed excessive amount of fatty tissue in the pelvis encasing the urinary bladder, causing compression of both distal ureters (Fig. 2a, 2b). The “tear-drop” shape of the bladder was again observed on the reconstructed images of the CT IVP (Fig. 3a, 3b). A suspicion of liposarcoma was raised based on the CT scan findings, following which the patient underwent surgical exploration. An intraoperative biopsy taken from the pelvic mass on histopathology confirmed the presence of benign lipomatous tissue and absence of malignancy. A diagnosis of Pelvic lipomatosis (PL) was made based on the histopathology report and the imaging findings. The patient was discharged and advised regular follow-up with renal function tests and CT scan.

1. Background 

Pelvic lipomatosis is an uncommon benign condition characterized by excessive deposition of fat in the pelvis due to overgrowth of adipose cells, resulting in compression of the pelvic organs. The term was coined in 1968 by Fogg et al., after studying 6 cases of high fixation of the urinary bladder and colon with imaging appearances simulating a pelvic neoplasm, but showing disproportionate amounts of fat in the pelvis on laparotomy [1]. Imaging plays a pivotal role in the diagnosis of pelvic lipomatosis. CT scans are considered to be the modality of choice, ensuring dependable diagnosis of the condition, because the absorption coefficient of the intrapelvic fatty tissue calculated (in Hounsfield units) by computer is clearly distinct from that of other tissues [2].

2. Pathophysiology and clinical features:

The aetiology has not yet been established. However, it has been postulated that it might be associated with chronic pelvic inflammation secondary to chronic urinary tract infection [3]. Some authors have proposed that this disease is a manifestation of generalized obesity [4]. There is a greater prevalence in males and African Americans [4].

PL presents with a broad range of symptoms, usually due to compression of the pelvic structures. The urinary tract, the lower intestinal tract and/or the vascular system may be compressed. On physical examination, one may observe urinary retention, presence of a palpable mass in the hypogastric region, elevation of the prostate on digital rectal examination, lower limb oedema, or arterial hypertension [4]. Delayed complications include obstructive renal failure, cystitis and bladder adenocarcinoma [4].

Imaging Features: 

On ultrasound, echogenic fatty tissue is seen surrounding a deformed bladder and sigmoid colon. Prior to advent of CT scan and MRI, IVP was useful in demonstrating the characteristic “pear-shaped” appearance of the urinary bladder. Nowadays, cross-sectional imaging modalities such as CT or MRI are central to the diagnosis of pelvic lipomatosis, as they also help in quantification and demonstrating the extent of the disease, as well as ruling out the concomitant presence of a soft tissue mass. The pelvis appears congested due to excessive amounts of fat surrounding the pelvic organs. However, no true soft-tissue mass is seen. On administration of an iodinated contrast agent, the fat does not enhance [4]. The urinary bladder is extrinsically compressed by the extra-luminal fat, stretched out vertically, and elevated above the pelvic floor [4]. The tissue planes are typically well preserved.

Outcome:

Treatment options for PL are limited. Dietary modifications, antibiotics, steroids or radiotherapy have not demonstrated efficacy [4].

Complete surgical removal of the abnormal fatty tissue is challenging, and the clinical significance of this procedure is ambiguous [4]. Being a benign condition, patients can be advised to follow up with imaging and regular renal function tests, which may be affected secondary to long-standing obstructive uropathy.

Take-Home Message / Teaching Points:      

The ability to make a specific diagnosis of Pelvic lipomatosis without an invasive procedure is quite rewarding. Being aware of the characteristic imaging findings of this condition is thus important. Knowledge of this condition is also important, in order to avoid confusion with malignant pathologies such as liposarcoma.