Focal hepatic steatosis
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- updated 8 Apr 2023:
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Focal hepatic steatosis, also known as focal hepatosteatosis or (erroneously) focal fatty infiltration, represents small areas of liver steatosis. In many cases, the phenomenon is believed to be related to the haemodynamics of a third inflow.
Terminology
The term 'fatty infiltration of the liver' is often erroneously used to describe liver steatosis. Since fat is intracellular in liver steatosis, and not in the extracellular matrix, using infiltration to describe it is factually incorrect.
Epidemiology
Essentially the same as those that contribute to diffuse hepatic steatosis 1,5:
alcohol abuse
exogenous steroids
drugs (amiodarone, methotrexate, chemotherapy)
IV hyperalimentation
In general, the treatment of the underlying condition will reverse the findings.
Pathology
Location
A characteristic location for focal hepatosteatosis is the medial segment of the left lobe of the liver (segment 4) either anterior to the porta hepatis or adjacent to the falciform ligament 1. This distribution is the same as that seen in focal fatty sparing and is thought to relate to variations in vascular supply. This also would account for focal fatty change/sparing sometimes seen related to vascular lesions.
Radiographic features
Ultrasound
Ultrasound features only become apparent when the amount of fat reaches 15-20%. Features include:
hyperattenuation of the beam
mild or absent positive mass effect
geographic borders
no distortion of vessels
inability to visualise the portal vein walls (as the parenchyma is as bright as the wall)
CT
-
decreased attenuation (non-contrast CT)
normal liver 50-57 HU
decreases by 1.6 HU per mg of fat in each gram of liver
-
decreased attenuation (post-contrast CT)
liver and spleen should normally be similar on delayed (70 seconds) scans
earlier scans are unreliable as the spleen enhances earlier than the liver (systemic supply rather than portal)
MRI
MRI is the imaging modality of choice in any case where the diagnosis is felt to be less than certain
increased T1 signal
signal drop-out on opposed-phase imaging
ability to quantify the fat fraction
Differential diagnosis
When located in characteristic locations then there is usually little difficulty in making the correct diagnosis. If unusual in location or appearance then differentials to be considered include:
-
the commonest hyperechoic liver lesion, typically well defined and may show peripheral feeding vessels
-<p><strong>Focal hepatic steatosis</strong>, also known as <strong>focal hepatosteatosis</strong> or (erroneously) <strong>focal fatty infiltration</strong>, represents small areas of <a href="/articles/hepatic-steatosis">liver steatosis</a>. In many cases, the phenomenon is believed to be related to the haemodynamics of a <a href="/articles/third-inflow">third inflow</a>. </p><h4>Terminology</h4><p>The term 'fatty infiltration of the liver' is often erroneously used to describe liver steatosis. Since fat is intracellular in liver steatosis, and not in the extracellular matrix, using infiltration to describe it is factually incorrect.</p><h4>Epidemiology</h4><p>Essentially the same as those that contribute to <a href="/articles/diffuse-hepatic-steatosis">diffuse hepatic steatosis</a> <sup>1,5</sup>:</p><ul>-<li><p><a href="/articles/diabetes-mellitus">diabetes mellitus</a></p></li>-<li><p><a href="/articles/obesity">obesity</a></p></li>-<li><p>alcohol abuse</p></li>-<li><p>exogenous steroids</p></li>-<li><p>drugs (amiodarone, methotrexate, chemotherapy)</p></li>-<li><p>IV hyperalimentation</p></li>-</ul><p>In general, the treatment of the underlying condition will reverse the findings.</p><h4>Pathology</h4><h5>Location</h5><p>A characteristic location for focal hepatosteatosis is the medial segment of the left lobe of the liver (<a href="/articles/couinaud-classification-of-hepatic-segments">segment 4</a>) either anterior to the <a href="/articles/porta-hepatis">porta hepatis</a> or adjacent to the <a href="/articles/falciform-ligament">falciform ligament</a> <sup>1</sup>. This distribution is the same as that seen in <a href="/articles/focal-fatty-sparing-of-the-liver">focal fatty sparing</a> and is thought to relate to variations in vascular supply. This also would account for focal fatty change/sparing sometimes seen related to vascular lesions.</p><h4>Radiographic features</h4><h5>Ultrasound</h5><p>Ultrasound features only become apparent when the amount of fat reaches 15-20%. Features include:</p><ul>-<li><p><a href="/articles/increased-hepatic-echogenicity">increased hepatic echogenicity</a></p></li>-<li><p>hyperattenuation of the beam</p></li>-<li><p>mild or absent positive mass effect</p></li>-<li><p>geographic borders</p></li>-<li><p>no distortion of vessels</p></li>-<li><p>inability to visualise the portal vein walls (as the parenchyma is as bright as the wall)</p></li>-</ul><h5>CT</h5><ul>-<li>-<p>decreased attenuation (non-contrast CT)</p>-<ul>-<li><p>normal liver 50-57 HU</p></li>-<li><p>decreases by 1.6 HU per mg of fat in each gram of liver</p></li>-</ul>-</li>-<li>-<p>decreased attenuation (post-contrast CT)</p>-<ul>-<li><p>liver and spleen should normally be similar on delayed (70 seconds) scans</p></li>-<li><p>earlier scans are unreliable as the spleen enhances earlier than the liver (systemic supply rather than portal)</p></li>-</ul>-</li>-</ul><h5>MRI</h5><p>MRI is the imaging modality of choice in any case where the diagnosis is felt to be less than certain</p><ul>-<li><p>increased T1 signal</p></li>-<li><p>signal drop-out on opposed-phase imaging</p></li>-<li><p>ability to quantify the fat fraction</p></li>-</ul><h4>Differential diagnosis</h4><p>When located in characteristic locations then there is usually little difficulty in making the correct diagnosis. If unusual in location or appearance then differentials to be considered include:</p><ul>-<li>-<p><a href="/articles/hepatic-haemangioma-3">hepatic haemangioma</a></p>-<ul><li><p>the commonest <a href="/articles/hyperechoic-liver-lesions">hyperechoic liver lesion</a>, typically well defined and may show peripheral feeding vessels</p></li></ul>-</li>-<li><p><a href="/articles/hepatic-abscess-1">hepatic abscess</a></p></li>-<li>-<p><a href="/articles/liver-tumours">liver neoplasms</a></p>-<ul>-<li><p><a href="/articles/primary-liver-tumours">primary liver tumours</a></p></li>-<li><p><a href="/articles/hepatic-metastases">hepatic metastases</a></p></li>-</ul>-</li>- +<p><strong>Focal hepatic steatosis</strong>, also known as <strong>focal hepatosteatosis</strong> or (erroneously) <strong>focal fatty infiltration</strong>, represents small areas of <a href="/articles/hepatic-steatosis">liver steatosis</a>. In many cases, the phenomenon is believed to be related to the haemodynamics of a <a href="/articles/third-inflow">third inflow</a>. </p><h4>Terminology</h4><p>The term 'fatty infiltration of the liver' is often erroneously used to describe liver steatosis. Since fat is intracellular in liver steatosis, and not in the extracellular matrix, using infiltration to describe it is factually incorrect.</p><h4>Epidemiology</h4><p>Essentially the same as those that contribute to <a href="/articles/diffuse-hepatic-steatosis">diffuse hepatic steatosis</a> <sup>1,5</sup>:</p><ul>
- +<li><p><a href="/articles/diabetes-mellitus">diabetes mellitus</a></p></li>
- +<li><p><a href="/articles/obesity">obesity</a></p></li>
- +<li><p>alcohol abuse</p></li>
- +<li><p>exogenous steroids</p></li>
- +<li><p>drugs (amiodarone, methotrexate, chemotherapy)</p></li>
- +<li><p>IV hyperalimentation</p></li>
- +</ul><p>In general, the treatment of the underlying condition will reverse the findings.</p><h4>Pathology</h4><h5>Location</h5><p>A characteristic location for focal hepatosteatosis is the medial segment of the left lobe of the liver (<a href="/articles/couinaud-classification-of-hepatic-segments">segment 4</a>) either anterior to the <a href="/articles/porta-hepatis">porta hepatis</a> or adjacent to the <a href="/articles/falciform-ligament">falciform ligament</a> <sup>1</sup>. This distribution is the same as that seen in <a href="/articles/focal-fatty-sparing-of-the-liver">focal fatty sparing</a> and is thought to relate to variations in vascular supply. This also would account for focal fatty change/sparing sometimes seen related to vascular lesions.</p><h4>Radiographic features</h4><h5>Ultrasound</h5><p>Ultrasound features only become apparent when the amount of fat reaches 15-20%. Features include:</p><ul>
- +<li><p><a href="/articles/increased-hepatic-echogenicity">increased hepatic echogenicity</a></p></li>
- +<li><p>hyperattenuation of the beam</p></li>
- +<li><p>mild or absent positive mass effect</p></li>
- +<li><p>geographic borders</p></li>
- +<li><p>no distortion of vessels</p></li>
- +<li><p>inability to visualise the portal vein walls (as the parenchyma is as bright as the wall)</p></li>
- +</ul><h5>CT</h5><ul>
- +<li>
- +<p>decreased attenuation (non-contrast CT)</p>
- +<ul>
- +<li><p>normal liver 50-57 HU</p></li>
- +<li><p>decreases by 1.6 HU per mg of fat in each gram of liver</p></li>
- +</ul>
- +</li>
- +<li>
- +<p>decreased attenuation (post-contrast CT)</p>
- +<ul>
- +<li><p>liver and spleen should normally be similar on delayed (70 seconds) scans</p></li>
- +<li><p>earlier scans are unreliable as the spleen enhances earlier than the liver (systemic supply rather than portal)</p></li>
- +</ul>
- +</li>
- +</ul><h5>MRI</h5><p>MRI is the imaging modality of choice in any case where the diagnosis is felt to be less than certain</p><ul>
- +<li><p>increased T1 signal</p></li>
- +<li><p>signal drop-out on opposed-phase imaging</p></li>
- +<li><p>ability to quantify the fat fraction</p></li>
- +</ul><h4>Differential diagnosis</h4><p>When located in characteristic locations then there is usually little difficulty in making the correct diagnosis. If unusual in location or appearance then differentials to be considered include:</p><ul>
- +<li>
- +<p><a href="/articles/hepatic-haemangioma-3">hepatic haemangioma</a></p>
- +<ul><li><p>the commonest <a href="/articles/hyperechoic-liver-lesions">hyperechoic liver lesion</a>, typically well defined and may show peripheral feeding vessels</p></li></ul>
- +</li>
- +<li><p><a href="/articles/hepatic-abscess-1">hepatic abscess</a></p></li>
- +<li>
- +<p><a href="/articles/liver-tumours">liver neoplasms</a></p>
- +<ul>
- +<li><p><a href="/articles/primary-liver-tumours">primary liver tumours</a></p></li>
- +<li><p><a href="/articles/hepatic-metastases">hepatic metastases</a></p></li>
- +</ul>
- +</li>
References changed:
- 1. Sohn J, Siegelman E, Osiason A. Unusual Patterns of Hepatic Steatosis Caused by the Local Effect of Insulin Revealed on Chemical Shift MR Imaging. AJR Am J Roentgenol. 2001;176(2):471-4. <a href="https://doi.org/10.2214/ajr.176.2.1760471">doi:10.2214/ajr.176.2.1760471</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/11159098">Pubmed</a>
- 2. Lupsor M & Badea R. Imaging Diagnosis and Quantification of Hepatic Steatosis: Is It an Accepted Alternative to Needle Biopsy? Rom J Gastroenterol. 2005;14(4):419-25. - <a href="https://www.ncbi.nlm.nih.gov/pubmed/16400362">Pubmed</a>
- 3. del Pilar Fernandez M & Bernardino M. Hepatic Pseudolesion: Appearance of Focal Low Attenuation in the Medial Segment of the Left Lobe at CT Arterial Portography. Radiology. 1991;181(3):809-12. <a href="https://doi.org/10.1148/radiology.181.3.1947102">doi:10.1148/radiology.181.3.1947102</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/1947102">Pubmed</a>
- 1. Sohn J, Siegelman E, Osiason A. Unusual patterns of hepatic steatosis caused by the local effect of insulin revealed on chemical shift MR imaging. AJR Am J Roentgenol. 2001;176 (2): 471-4. <a href="http://www.ajronline.org/cgi/content/full/176/2/471">AJR Am J Roentgenol (full text)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/11159098">Pubmed citation</a><div class="ref_v2"></div>
- 2. Lupsor M, Badea R. Imaging diagnosis and quantification of hepatic steatosis: is it an accepted alternative to needle biopsy? Rom J Gastroenterol. 2005;14 (4): 419-25. <a href="http://www.jgld.ro/42005/42005_16.html">Rom J Gastroenterol (link)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/16400362">Pubmed citation</a><div class="ref_v2"></div>
- 3. Del pilar fernandez M, Bernardino ME. Hepatic pseudolesion: appearance of focal low attenuation in the medial segment of the left lobe at CT arterial portography. Radiology. 1991;181 (3): 809-12. <a href="http://radiology.rsna.org/content/181/3/809.abstract">Radiology (abstract)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/1947102">Pubmed citation</a><div class="ref_v2"></div>
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