Secondaries (Metastatic Tumors) in the Liver - Pathology

1. General Overview

• Secondaries are the most common malignant tumors of the liver - far more frequent than primary liver cancers
• The liver is one of the most common sites for metastatic spread, second only to regional lymph nodes
• Clinically detected in ~40% of all cancer autopsies
• Often bilateral and multiple at the time of diagnosis

2. Routes of Spread

3. Common Primary Sites

4. Gross Pathology

• Number: Typically multiple (>90% are multiple); solitary met is rare but does occur (especially CRC)
• Size: Variable - mm to several cm; may replace virtually the entire liver
• Distribution: Both lobes affected in most cases
• Surface: Liver surface shows multiple "cannon ball" nodules, often described as umbilicated (central depression due to ischemic necrosis)
• Central umbilication: A hallmark feature - results from rapid tumor growth outstripping blood supply, causing central necrosis
• Cut surface: Pale/white to yellowish nodules with surrounding hyperemic rim
• Mucin-secreting tumors (e.g., mucinous CRC): gelatinous/glistening deposits
• Melanoma mets: Black/dark brown
• Carcinoid mets: Yellow-orange, often large, sometimes with calcification
• Overall liver: May be massively enlarged (hepatomegaly), sometimes weighing >5 kg

5. Microscopic (Histological) Features

• Architecture reflects the primary tumor - this is the key principle in identifying the site of origin
• Deposits are surrounded by a compressed rim of normal liver tissue ("pseudocapsule")
• Desmoplastic stroma around metastatic deposits (especially CRC) - distinguishes from HCC
• Central coagulative necrosis is common in large deposits
• Vascular invasion within the deposit may be seen
• No liver cell dysplasia in surrounding parenchyma (unlike HCC, which arises in cirrhosis)
• Surrounding liver is typically non-cirrhotic - important distinguishing feature

Specific Histological Patterns:

6. Immunohistochemistry (IHC) for Identification

7. Compared to Primary HCC

8. Special Patterns

• Miliary metastases: Tiny (<5 mm) deposits throughout - typical of breast cancer and melanoma
• Diffuse infiltration: Metastases replace normal liver parenchyma diffusely without forming distinct nodules - rare, seen in gastric/breast signet ring
• Perivascular cuffing: Deposits concentrate around portal tracts (lymphangitic spread)
• Synchronous vs. Metachronous: Synchronous = detected at same time as primary; metachronous = detected later

9. Complications of Hepatic Secondaries

1. Hepatic failure - from massive replacement of parenchyma
2. Portal hypertension - from compression of portal venules
3. Obstructive jaundice - deposits at porta hepatis
4. Spontaneous rupture - rare, can cause hemoperitoneum
5. Budd-Chiari syndrome - tumor thrombus occluding hepatic veins
6. Paraneoplastic syndromes - hypoglycemia (especially with NETs)

10. Frozen Section / Biopsy Points

• Core biopsy under imaging guidance is the standard for tissue diagnosis
• Imprint cytology may be done intraoperatively
• Key reporting: number of deposits, size of largest, closest margin (in resection), presence of vascular invasion, lymph node status (porta hepatis)

Key Exam Points (Pathology Perspective)

1. Most common malignant liver tumor = secondary (not HCC)
2. Most common primary = colorectal
3. Gross: multiple, umbilicated nodules in non-cirrhotic liver
4. Central umbilication = ischemic necrosis of rapidly growing tumor
5. Histology mirrors primary; desmoplasia = hallmark of CRC metastasis
6. Non-cirrhotic background = favors secondary over HCC
7. IHC panel (CK7/CK20/CDX2/TTF-1) used to trace origin
8. Melanoma mets are black due to melanin
9. Carcinoid/NET mets are yellow-orange and may calcify
10. "Cannon ball" appearance on imaging and gross pathology

Steatohepatitis - Complete Pathology Notes

1. Definition

• ASH - Alcoholic steatohepatitis (part of alcohol-associated liver disease)
• MASH/NASH - Metabolic dysfunction-associated steatohepatitis / Non-alcoholic steatohepatitis (part of NAFLD/MASLD)

2. Types of Steatosis (Background)

• Macrovesicular steatosis is the predominant form in both alcoholic and non-alcoholic steatohepatitis
• ASH may rarely show alcoholic foamy degeneration (diffuse microvesicular-to-macrovesicular steatosis with ER and mitochondrial damage)

3. Alcoholic Steatohepatitis (ASH)

Pathogenesis

• Threshold: 80 g/day alcohol causes steatosis; 80-160 g/day for years leads to hepatitis; only 10-15% develop cirrhosis despite heavy drinking
• Women are more susceptible at lower doses (>20 g/day vs. >60-80 g/day in men); peak incidence ~a decade earlier

1. Altered redox state - Alcohol dehydrogenase (ADH) + aldehyde dehydrogenase generate NADH, shifting redox balance to favor lipogenesis and suppress fatty acid oxidation
2. Acetaldehyde toxicity - Lipid peroxidation, acetaldehyde-protein adduct formation, disrupts cytoskeleton and membranes, produces neoantigens
3. CYP2E1 induction - Generates ROS that damage proteins, membranes, mitochondria; promotes apoptosis; also converts drugs like acetaminophen to toxic metabolites
4. Methionine metabolism impairment - Decreases glutathione, sensitizes to oxidative injury; elevates homocysteine causing ER stress
5. Gut permeability - Increased gut permeability releases endotoxin (LPS) into portal blood, activating Kupffer cells via TLR4, releasing pro-inflammatory cytokines (TNF-α, IL-1β, caspase-1 via inflammasome)
6. Impaired lipoprotein assembly and secretion
7. Enhanced peripheral fat catabolism - Increases circulating FFA available to hepatocytes

• Amount and duration of alcohol (most important)
• Female sex
• Genetic factors: PNPLA3, HSD17B13, TM6SF2, MBOAT7, MARC1 polymorphisms
• Protein-calorie malnutrition
• Comorbid hepatitis B/C, hemochromatosis, MASLD
• Obesity

Morphology (MORPHOLOGY section, Robbins Cotran)

• Macroscopically: enlarged (up to 4-6 kg), soft, yellow, greasy liver
• Lipid droplets accumulate as small droplets → coalesce into large single droplet → push nucleus to periphery
• Predominantly macrovesicular, centrilobular
• Completely reversible with abstinence

1. Ballooned hepatocytes - Injured, swollen hepatocytes with cleared-out cytoplasm and cytoskeletal damage. When extensive, leads to Mallory hyaline formation. Essential for diagnosis. On CK8/18 immunostaining: keratins are collapsed, leaving cytoplasm "empty."
2. Mallory-Denk bodies (Mallory hyaline) - Irregular eosinophilic intracytoplasmic inclusions composed of ubiquitinated, partially degraded intermediate filaments (keratin 8 and 18). Represent a failed attempt to sequester damaged cytoplasmic proteins. More abundant in ASH than MASH. Also seen in: Wilson disease, chronic biliary diseases, MASH.
3. Neutrophilic inflammation - Neutrophils are more prominent in ASH than in MASH; localize around ballooned hepatocytes (especially those with Mallory hyaline) - called "satellitosis". Lymphocytes are also present in portal tracts.
4. Perivenular/pericellular fibrosis ("chicken wire" fibrosis) - Fibrosis starts in acinar zone 3 as perisinusoidal/pericellular fibrosis with a "chicken wire" appearance (best seen on Masson trichrome stain). This is the earliest fibrotic change.

• Zone 3 pericellular fibrosis → portal/periportal fibrosis → bridging fibrosis → cirrhosis
• Micronodular cirrhosis ("Laennec cirrhosis") - average nodule ~3 mm, greenish tint from cholestasis
• "Burned-out" cirrhosis: fatty change disappears; small nodules trapped in blue-staining fibrous tissue
• Vascular derangements: phlebosclerosis (fibrous obliteration of central veins) + veno-occlusive lesions
• Early fibrosis can regress with abstinence; cirrhosis rarely fully regresses

4. Non-Alcoholic Steatohepatitis (NASH / MASH)

Definition / Terminology

• NAFLD = Non-alcoholic fatty liver disease (spectrum: simple steatosis → NASH → cirrhosis)
• MASLD = Metabolic dysfunction-associated steatotic liver disease (new 2023 nomenclature)
• NASH = Non-alcoholic steatohepatitis (now also called MASH = Metabolic dysfunction-associated steatohepatitis)
• Histologically resembles ASH but occurs without significant alcohol consumption (>2 drinks/day in men, >1 in women excludes NAFLD)

Risk Factors (Metabolic Syndrome)

• ~80% of T2DM patients and ~90% of morbidly obese individuals have imaging evidence of NAFLD
• ~1/3 of adults in Western countries have NAFLD; ~5% have NASH
• Hispanics and Whites at higher risk; lower prevalence in African Americans

Pathogenesis ("Two-Hit" Model, now multi-hit)

• 1st hit: Insulin resistance + hyperinsulinemia → excessive FFA uptake by hepatocytes → macrovesicular steatosis (predominantly centrilobular)
• 2nd hit: Lipotoxicity from unesterified FFAs (especially palmitic acid, cholesterol, lysophosphatidylcholine, ceramides) → oxidative stress, ER stress, mitochondrial dysfunction, apoptosis
• Additional factors: adipocytokines (↓adiponectin, ↑TNF-α), gut dysbiosis, stellate cell activation
• PNPLA3 genetic polymorphisms correlate with severity of steatosis and fibrosis

Morphology of NASH

• Macrovesicular steatosis (centrilobular, zone 3)
• Ballooning degeneration of hepatocytes
• Mallory-Denk bodies (less abundant than in ASH)
• Lobular inflammation
• Pericellular/perisinusoidal "chicken wire" fibrosis (zone 3)
• Can progress to cirrhosis and HCC

5. NASH Activity Score (NAS) - Kleiner Scoring System

• NAS ≥5 = definite NASH; NAS ≤4 does not exclude NASH (75% with NAS ≥5 had definite steatohepatitis)
• Steatohepatitis is a pattern diagnosis (steatosis + inflammation + ballooning); NAS alone cannot diagnose it

6. Drug-Induced Steatohepatitis

• Amiodarone (most classic - causes phospholipidosis + steatohepatitis + fibrosis)
• Tamoxifen
• Methotrexate (causes steatohepatitis + portal fibrosis)
• Glucocorticoids
• Valproic acid (causes microvesicular steatosis)
• Antiretrovirals (didanosine, stavudine)

7. Progression and Outcomes

• Simple steatosis → NASH (in ~20% over years)
• NASH → cirrhosis (in ~15-25% over 10-15 years)
• Cirrhosis → HCC (steatohepatitis-related HCC can also arise without cirrhosis, especially in NASH)
• NAFLD is now a leading cause of liver transplantation

8. Key Exam Points

1. Cardinal histological tetrad: macrovesicular steatosis + ballooning + Mallory-Denk bodies + neutrophilic infiltrate
2. Mallory hyaline = ubiquitinated keratin 8/18 intermediate filaments; eosinophilic intracytoplasmic; more in ASH than NASH
3. Zone 3 (centrilobular) is the primary site of both steatosis and fibrosis onset
4. Chicken wire fibrosis = perisinusoidal/pericellular fibrosis on Masson trichrome; earliest fibrosis pattern
5. Satellitosis = neutrophils surrounding a ballooned hepatocyte with Mallory body
6. ASH vs NASH: histologically similar - key clinical differentiator is alcohol history; AST:ALT >2 favors ASH; ALT rarely >150 in ASH
7. Laennec cirrhosis = micronodular cirrhosis from chronic alcohol use
8. Phlebosclerosis = fibrous obliteration of terminal hepatic venules; portal hypertension without traditional hepatic causes
9. NASH progresses to HCC even without cirrhosis - unique among chronic liver diseases
10. Pediatric NAFLD: type 2 pattern = portal inflammation + portal fibrosis, no ballooning (zone 1 predominant)