Pseudolipoma of the Glissonian capsule mimicking hepatic metastases after surgery for colorectal cancer: The role of dual-energy CT

Abstract

Pseudolipoma of the Glisson’s capsule is a rare benign lesion caused by the detachment and sequestration of peritoneal fat on the liver surface, often originating from the displacement of an epiploic appendage during colorectal surgery. Its imaging appearance, especially on CT, can mimic hepatic metastases, posing a diagnostic challenge, particularly in oncologic patients. We present the case of a patient who had undergone surgery for colorectal carcinoma in 2022 and underwent a CT scan during oncologic follow-up 2 years after the procedure. Dual-energy CT allowed for a precise differential diagnosis, clearly distinguishing the pseudolipoma from liver metastases. To our knowledge, this is the first reported case of pseudolipoma of the Glisson’s capsule evaluated using dual-energy CT, allowing for an accurate differentiation from hepatic metastases.

Introduction

Pseudolipoma of the Glisson’s capsule is a rare, benign lesion, most commonly resulting from the detachment and subsequent adhesion of epiploic appendages to the liver surface, typically following colorectal surgery [1,2]. Although usually asymptomatic and incidentally detected, its imaging appearance can closely mimic that of hepatic metastases, particularly in oncologic patients, posing a significant diagnostic challenge [[3], [4], [5], [6], [7]]. Conventional imaging may be inconclusive, especially when the lesion lacks overt fatty attenuation. Dual-energy computed tomography (DECT) has emerged as a valuable tool for tissue characterization, offering spectral analysis and material decomposition techniques that enhance the detection of fat-containing lesions.

Case report

A 77-year-old male patient with a medical history of type II diabetes mellitus and benign prostatic hyperplasia underwent left hemicolectomy in September 2022 for moderately differentiated colonic adenocarcinoma. Histopathological examination revealed tumor infiltration of the perivisceral fat and lymph node involvement (2 positive lymph nodes out of 12 removed), corresponding to stage pT3, N1, M0. The patient subsequently received adjuvant chemotherapy with the mFOLFOX-6 regimen. Follow-up clinical, laboratory, and imaging evaluations showed no evidence of disease recurrence or progression.

In February 2024, the patient underwent follow-up imaging with a multiphasic contrast-enhanced CT scan. The examination was performed using a dual-energy, dual-layer CT scanner (IQon Spectral CT, Philips Healthcare, Best, The Netherlands) with the following acquisition parameters: tube voltage of 120 kVp with automatic mAs modulation; nominal slice thickness of 0.67 mm; scan interval of 0.34 mm; detector collimation of 64 × 0.625 mm; tube rotation time of 0.27 s; and a 512 × 512 matrix. The patient received an intravenous injection of 1.2 mL/kg of a nonionic contrast agent (Iomeprol, 400 mg iodine/mL; Iomeron 400; Bracco Diagnostics, Princeton, NJ) at a rate of 3.5 mL/s, followed by 30 mL of saline solution at the same flow rate, administered using an automatic injector.

The CT examination revealed a 15-mm hypodense lesion in the peripheral region of hepatic segment VI, raising suspicion of metastatic disease (Fig. 1).

Fig. 1.

Axial contrast-enhanced CT image in the portal venous phase showing a 15-mm hypodense lesion in the peripheral portion of hepatic segment VI (arrow), raising suspicion for metastatic disease.

Subsequently, virtual monoenergetic images (VMI) were reconstructed at energy levels ranging from 40 keV to 200 keV using the iterative reconstruction algorithm iDose4, with a slice thickness of 2 mm and a reconstruction interval of 2 mm. Image processing was performed using dedicated software (Philips Intellispace Portal 11.1). Virtual monoenergetic images (VMI) were utilized to generate spectral Hounsfield unit (HU) curves on a dedicated workstation. Hounsfield unit values were measured by placing regions of interest (ROIs) in 3 different areas: the suspected hepatic lesion, the normal liver parenchyma, and the subcutaneous fat. The average CT attenuation values were recorded across a range of monochromatic energy levels (40-200 keV), allowing for the construction of spectral HU curves for each ROI, aiding in the lesion’s characterization. The spectral HU curves demonstrated a reduction in attenuation values for both the suspected Glisson’s capsule lesion and the subcutaneous fat at low keV levels, consistent with the presence of an adipose component (Fig. 2).

Fig. 2.

Unenhanced monochromatic 70 keV CT image with 3 regions of interest (ROIs) placed in the suspected hypodense lesion, subcutaneous fat, and normal hepatic parenchyma. Spectral attenuation curves derived from monochromatic images (40-200 keV) demonstrate a similar pattern of decreasing attenuation at lower energy levels for both the hypodense lesion and subcutaneous fat, consistent with adipose tissue characteristics.

Spectral CT imaging further supported the diagnostic hypothesis by generating fat maps, enabled by material decomposition algorithms, that confirmed the fatty nature of the lesion (Fig. 3).

Fig. 3.

Spectral CT fat map obtained through material decomposition algorithms, demonstrating the fatty composition of the lesion (arrow), consistent with a pseudolipoma of the Glisson's capsule (subcutaneous fat, asterisk).

These characteristic spectral behaviors, combined with the patient’s history of previous colorectal surgery, suggested the diagnosis of a pseudolipoma of the Glisson’s capsule, rather than a metastatic lesion.

To further support the suspected diagnosis of pseudolipoma of the Glisson’s capsule, the patient underwent magnetic resonance imaging (MRI) with in-phase and out-of-phase sequences, which confirmed the presence of intralesional fat, reinforcing the suspicion of a pseudolipoma of the Glisson’s capsule (Fig. 4). Additionally, diffusion-weighted imaging (DWI) and hepatospecific contrast-enhanced MRI ruled out the presence of other lesions suspicious for metastatic disease. At a 6-month follow-up MRI, the lesion remained stable in size and appearance, with no changes suggestive of progression or malignant transformation, further supporting its benign nature (Fig. 5).

Fig. 4.

Axial gradient-echo T1-weighted magnetic resonance images acquired in-phase (A) and out-of-phase (B). A signal drop in the out-of-phase image confirms the presence of intralesional fat, supporting the diagnosis of a pseudolipoma of the Glisson’s capsule.

Fig. 5.

Axial gradient-echo T1-weighted magnetic resonance images acquired in-phase (A) and out-of-phase (B) at 6-month follow-up, showing no signal variation or change in lesion size, consistent with stability of the imaging finding.

Discussion

Pseudolipoma of the Glisson’s capsule is an uncommon benign lesion resulting from the detachment and sequestration of peritoneal fat on the liver surface [1,2].

It is widely recognized that pseudolipomas often originate from displaced epiploic appendages, which become adherent to the liver following abdominal surgery or peritoneal inflammation [[3], [4], [5], [6], [7]].

Other potential causes of pseudolipoma of Glisson’s capsule include the entrapment of fat within the liver capsule due to surgical trauma or percutaneous liver biopsy [3].

Reported cases of liver pseudolipoma are rare, with an estimated prevalence of 0.2% and a mean patient age of 67 years [1].

As the condition is typically asymptomatic, treatment is generally not required.

Pseudolipomas are most often detected incidentally and can present a significant diagnostic challenge in oncologic patients due to their potential to mimic hepatic metastases on imaging studies [8].

On conventional CT, these subcapsular lesions typically exhibit low attenuation values but often lack definitive negative Hounsfield Units (−30 to −90 HU) characteristic of pure fat. This occurs because of internal degenerative transformations, chronic fat necrosis, or progressive fibrous encapsulation, which elevate the baseline density. Consequently, on portal venous phase CT, a pseudolipoma may appear as a nonenhancing hypodense nodule, mimicking avascular or necrotic hepatic metastases. Furthermore, the surrounding hepatic capsule can sometimes create a thin peripheral rim that falsely simulates a target-like enhancement pattern, further compounding the diagnostic pitfall.

Differentiating these lesions from malignant liver tumors is essential to avoid unnecessary biopsies, additional imaging, or inappropriate treatment strategies [[4], [5], [6], [7]].

The clinical significance of an accurate, noninvasive diagnosis of Glisson’s capsule pseudolipoma is paramount in oncologic follow-up. Misinterpreting this benign entity as a metastatic recurrence can lead to devastating consequences for the patient, including severe psychological distress and erroneous tumor upstaging. Furthermore, invasive procedures like percutaneous liver biopsies carry inherent risks of bleeding or tumor seeding, which can be safely avoided through precise advanced imaging interpretation.

In our case, dual-energy CT was instrumental in refining the diagnosis. The application of virtual monoenergetic imaging (VMI) and spectral HU curve analysis allowed for a more detailed assessment of the lesion’s composition [9].

By placing a region of interest (ROI) on the suspected lesion and analyzing attenuation values at different energy levels (40-200 keV), we observed a progressive decrease in attenuation with decreasing energy, confirming the presence of intralesional fat.

In addition, material decomposition algorithms allowed for the generation of fat density maps, which visually confirmed the adipose nature of the lesion and further supported the diagnosis of a pseudolipoma of Glisson’s capsule.

This spectral behavior was key in differentiating the pseudolipoma from metastatic disease, as it provided objective quantitative data supporting a benign fatty composition.

This case highlights the value of spectral CT in differentiating benign from malignant hepatic lesions, reinforcing its role as a powerful, noninvasive diagnostic tool in oncologic imaging.

Availability of data and materials

All data and materials relevant to this case report are available from the corresponding author on reasonable request.

Author contributions

All of the authors participated in the design of the study, acquisition, and interpretation of data, and drafting of the manuscript. All of the authors read and approved the final manuscript.

Patient consent

The authors declare that informed consent was obtained from the patient for the CT and MRI examinations, for the administration of intravenous contrast medium, and for the anonymous publication of radiological images and clinical history in a scientific journal.