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Difficulty: MediumPathology and Biopsy Interpretation

A 3434-year-old woman is referred to hepatology after a liver mass is discovered during an ultrasound for vague upper abdominal discomfort. She has a 1212-year history of combined oral contraceptive use. Liver biochemistries are within normal limits. Magnetic resonance imaging demonstrates a 5.55.5-cm, highly vascular, solid lesion in the right hepatic lobe. The imaging characteristics are indeterminate, lacking a definitive central scar or classical washout pattern. A percutaneous core needle biopsy is performed. Histopathologic evaluation reveals well-differentiated, cytologically bland hepatocytes arranged in nodules that are intersected by fibrous bands containing malformed, thick-walled arteries. Normal portal triads are absent. Immunohistochemical staining for glutamine synthetase exhibits a broad, anastomosing "map-like" pattern of strong positivity. Based on the histopathologic and immunohistochemical findings, what is the most appropriate diagnosis?

  1. Focal nodular hyperplasiaAnswer
  2. B
    Beta-catenin-activated hepatocellular adenoma
  3. C
    Inflammatory hepatocellular adenoma
  4. D
    Fibrolamellar hepatocellular carcinoma
  5. E
    Well-differentiated hepatocellular carcinoma

Answer

Focal nodular hyperplasia
The correct answer is Focal nodular hyperplasia. This condition represents a hyperplastic response to a localized vascular abnormality rather than a true neoplasm. Histologically, it lacks normal portal triads and features fibrous bands containing anomalous thick-walled arteries. Because differentiating this lesion from hepatic adenomas (which may require surgical resection) on imaging can sometimes be challenging, a biopsy is utilized. The "map-like" (anastomosing) pattern of glutamine synthetase expression is pathognomonic and highly specific for focal nodular hyperplasia.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and imaging.
A young woman with a history of oral contraceptive use has an indeterminate 5.55.5-cm hypervascular liver mass.
This demographic and presentation require differentiating between benign lesions (focal nodular hyperplasia, hepatic adenomas) and malignant lesions (hepatocellular carcinoma).
2
Evaluate the architectural histopathologic features from the biopsy.
The biopsy shows bland hepatocyte nodules, fibrous bands containing anomalous unpaired arteries, and a lack of normal portal triads.
These structural findings strongly suggest a localized hyperplastic response to a vascular anomaly rather than a true neoplasm.
3
Interpret the specific immunohistochemical staining pattern.
Glutamine synthetase staining is positive in a broad, anastomosing "map-like" distribution.
This specific staining pattern confirms the diagnosis of focal nodular hyperplasia and reliably differentiates it from various subtypes of hepatocellular adenoma.

Key Concept

Focal nodular hyperplasia (FNH) is characterized histologically by nodules of bland hepatocytes separated by fibrous septa containing dystrophic vessels, and immunohistochemically by a pathognomonic "map-like" pattern of glutamine synthetase staining.
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Topics

Pathology and Biopsy Interpretation

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