Teaching Case

52-year-old patient who suffered a splenic rupture caused by a motorbike accident. Previous medical history included acute myocardial infarction (AMI), smoking habit and chronic hepatopathy (HCV). 2 years after his accident a scheduled CT was performed.

Mortorbike accident:
An emergency CT scan showed a splenic haematoma of 16cm with active bleeding within it, which was stopped after an intravascular embolization (Fig. 1; note the artefact in the lower pole of the spleen). This first CT showed multifocal nodular hepatic lesions, mainly hypodense, associated to some diffuse hypodense hepatic areas (Fig. 1). These findings were oriented as multifocal nodular steatosis and follow-up CTs were recommended.

- 2 years after the accident:
Several CTs were performed during 2 years. The last programmed CT showed more multifocal nodular lesions and larger lesions (Fig. 2). A MRI was recommended.

Liver MRI showed multiple and uncountable nodular hepatic lesions which were clearly depicted on T1-weighted out-of-phase images and were slightly hyperintense on T2-weighted sequences. These lesions were not visible on T1 weighted in-phase sequences, diffusion or ADC. No contrast enhancement was observed. (Fig. 3, 4)

A sonography and a core-needle biopsy were performed. Biopsy confirmed the presence of macrovesicular steatosis. (Fig. 5)

BACKGROUND

Fatty liver is a term applied to triglyceride accumulation within the hepatocytes and tends to be most important around the central veins (hypoxic area).
The two most common conditions associated with fatty liver are alcoholic liver disease and nonalcoholic fatty liver disease (insulin resistance and metabolic syndrome).
Other conditions associated with steatosis include viral hepatitis and drugs. [1]

CLINICAL PERSPECTIVE

Steatosis may progress to steatohepatitis (inflammation and fibrosis) and then cirrhosis. Multifocal nodular fatty infiltration could be misdiagnosed as metastatic liver disease (for example, patients with a known malignancy) and incorrect therapy could be administered. [1, 5]

IMAGING PERSPECTIVE

Accumulation of fat within the liver can take different morphologies and patterns. Common patterns are diffuse fat accumulation (with or without focal sparing) and focal fat accumulation. Unusual patterns could mimic metastases or vascular diseases. [2, 3]
Multifocal nodular fatty infiltration is visualized as a highly echoic lesion on sonography, as a low-density area with no mass effect on CT. On MRI, these lesions are visualized as hypointense on T1-weighted out-of-phase images, isointense on T1-weighted in-phase images and slightly hyperintense on T2-weighted images. Correct diagnosis is difficult and sometimes requires a fine-needle aspiration or core-needle biopsy to prove the presence of fat within the lesion. [4, 5]

OUTCOME

Steatosis has a good prognosis if patients enrol on a diet (alcohol abstinence, limit high-carb foods and weight loss). Cirrhosis develops in approximately 1% to 2% of patients over 20 years.
On the other hand, steatohepatitis has a worse prognosis with 10% to 12% of patients progressing to cirrhosis within eight years. [6, 7]

TAKE HOME MESSAGE

- The two most common causes of steatosis: alcoholic liver disease and nonalcoholic fatty liver disease (insulin resistance and metabolic syndrome).

- Common patterns of fat accumulation: diffuse fat accumulation (with or without focal sparing) and focal fat accumulation.

- Unusual patterns as multifocal nodular fatty infiltration could mimic metastases.

- Multifocal nodular fatty infiltration: highly echoic lesions (US), low-density area with no mass effect (CT), hypointense on T1-weighted out-of-phase images, isointense on T1-weighted in-phase images and slightly hyperintense on T2-weighted images (MRI).

- Sometimes diagnosis requires a fine-needle aspiration or core-needle biopsy.

- Pathogenesis of multifocal nodular fat deposition in the liver is unknown.