Q. A 35-year-old woman undergoes abdominal imaging for nonspecific RUQ pain. A liver mass is identified and surgically excised. The gross specimen is shown below. What is the most likely diagnosis?

Explanation

## Correct Answer: A. Focal nodular hyperplasia Focal nodular hyperplasia (FNH) is the most common benign liver tumor in adults, characterized by a central scar with radiating fibrous septa—the pathognomonic gross finding. The clinical presentation of a 35-year-old woman with incidental RUQ mass on imaging is classic: FNH is typically asymptomatic and discovered incidentally during imaging for unrelated symptoms. Histologically, FNH shows benign hepatocytes arranged in nodules separated by fibrous tissue, with a central stellate scar containing abnormal vessels and bile ducts. The central scar is the discriminating feature—it represents a hamartomatous lesion arising from a developmental vascular anomaly. Unlike hepatic adenoma (which lacks a central scar and occurs in women on oral contraceptives), FNH does not undergo malignant transformation and requires no treatment. The gross specimen showing a well-demarcated mass with a central scar is diagnostic. FNH is more common in women but does not have the strong OCP association that adenoma does. The lesion is benign, non-progressive, and does not require follow-up or resection unless symptomatic—though this patient underwent excision, likely due to diagnostic uncertainty preoperatively. ## Why the other options are wrong **B. Hepatic adenoma** — Hepatic adenoma is a benign tumor that typically occurs in women on oral contraceptives and presents as a solitary, well-circumscribed mass WITHOUT a central scar. While both are benign, adenoma lacks the pathognomonic central stellate scar seen in FNH. Adenoma has higher risk of rupture and hemorrhage, and carries a small risk of malignant transformation. The absence of a central scar on gross examination rules out adenoma. **C. Hepatocellular carcinoma** — HCC typically presents with cirrhosis, elevated AFP, and imaging features of arterial enhancement with washout. This patient has no mention of cirrhosis, chronic liver disease, or elevated tumor markers. HCC is malignant with poor prognosis, whereas the benign appearance and central scar are inconsistent with HCC. The incidental discovery in a non-cirrhotic patient with a well-demarcated lesion makes HCC unlikely. **D. Metastasis** — Metastatic lesions are typically multiple, lack a central scar, and arise from primary malignancy elsewhere. The presence of a solitary, well-demarcated mass with a characteristic central scar is not typical of metastasis. No history of primary malignancy is mentioned, and the benign histology with normal hepatocytes rules out metastatic disease. ## High-Yield Facts - **Focal nodular hyperplasia** is the most common benign liver tumor, accounting for 8–17% of benign hepatic lesions in autopsy series. - **Central stellate scar** is the pathognomonic gross finding in FNH, representing a developmental vascular anomaly with radiating fibrous septa. - **No malignant potential**: FNH does not undergo transformation to HCC and requires no surveillance or treatment if asymptomatic. - **Female predominance** (female-to-male ratio ~5:1) but NO strong association with oral contraceptive use (unlike hepatic adenoma). - **Incidental discovery** on imaging for unrelated symptoms is the typical presentation; most FNH lesions are asymptomatic. - **Histology**: benign hepatocytes in nodular arrangement with fibrous septa; central scar contains abnormal vessels and bile ducts. ## Mnemonics **FNH vs Adenoma (SCAR rule)** **S**car = FNH; **C**ontracept = Adenoma; **A**denoma = no scar; **R**isk = Adenoma (rupture/bleed/malignancy). Use when differentiating benign liver tumors in women. **Central Scar = FNH** If you see a central stellate scar on gross specimen or imaging, think FNH first. It's the one benign tumor with this feature. Adenoma, HCC, and metastases do not have central scars. ## NBE Trap NBE may pair "benign liver tumor in a woman" with hepatic adenoma to trap students who over-associate adenoma with female gender, forgetting that FNH is actually more common overall and lacks the OCP-dependence of adenoma. The central scar is the key discriminator. ## Clinical Pearl In Indian clinical practice, FNH is often discovered incidentally on ultrasound or CT done for unrelated abdominal complaints (fever, dyspepsia, RUQ pain). Unlike adenoma, it requires no follow-up imaging, no OCP cessation, and no resection unless symptomatic—a key point for counseling patients and avoiding unnecessary interventions. _Reference: Robbins Ch. 18 (Liver and Biliary Tract); Harrison Ch. 297 (Liver Diseases)_