Applied Radiology

CASE SUMMARY

A 26-year-old woman with a history of duodenal ulcer and esophagogastric reflux disease, presented with epigastric pain radiating to the left upper quadrant for 2 days. The patient also had fever and nausea. A guaiac test was negative. There was no associated hematemesis or hemop-tysis. The patient was not anorexic and denied loss of weight. Her abdominal examination revealed right upper quadrant tenderness on palpa-tion. Hepatic biochemical tests showed abnormal liver function and increased billirubin. There was also slightly in-creased white blood cell count.

IMAGING FINDINGS

An ultrasound study demonstrated a large left upper quadrant mass in the splenetic hilar. A subsequent CT scan revealed a large mass involving the lateral segment of the left lobe of the liver, stomach, and splenic hilum, which contained cystic and solid areas (figure 1). A liver-spleen scan-SPECT (single photon emission computed tomography) with admini-stration of Technetium 99m-labeled sulfur colloid demonstrated a large defect involving the medial aspect of the spleen which appeared to com-press the left lobe of the liver anteriorly (figure 2).

DIAGNOSIS

Based on the imaging findings, the radiologic differential diagnoses include: 1) primary hepatic malignant neoplasm, such as necrotic hepato-cellular carcinoma; 2) primary hepatic non-malignant neoplasm with un-usual presentations, such as focal nodular hyperplasia (FNH); 3) gas-tric neoplasm with direct invasion of liver; 4) lymphoma; 5) metastatic di-sease from unknown origin; and 6) infection, although this is less likely.

The patient subsequently under-went surgery. A large left upper qua-drant tumor originating from the left lobe of the liver was identified. This mass did not involve the stomach. Needle aspiration showed profuse bleeding. Frozen section examination revealed necrotic tissue. Gross path-ology examination demonstrated a 10-cm well-demarcated mass, which had a multilobulated nodular appearance with a pale-yellow necrotic center and a thin peripheral rim (figure 3). Microscopic examination proved this mass to be FNH of the liver with multiple areas of necrosis. There was no evidence of hepatocyte atypia.

DISCUSSION

FNH occurs most commonly in middle-aged women. While its cause is not clearly understood, a relationship with oral contra-ceptives has been demonstrated. ^1,2 FNH is usually found incidentally at surgery or autopsy. Occasionally, it presents as a asymptomatic upper abdominal mass. Com-plications are rare, and malignant trans-formation does not occur. Pathologically, FNH lesions are usually < 5 cm in diameter; most have central scars containing thick-walled vessels that provide excellent arterial blood supply. Thus, infarction, necrosis, and hemorrhage are extremely unusual. ³ Usually, a pseudocapsule is present and the bulk of the lesion is composed of regenerating liver nodules with a fibrous center and portal areas containing proliferating ducts.

There is often excellent correlation be-tween the pathologic features of FNH (a characteristically homogenous hypervascu-lar tumor with a central scar and both he-patocellular and reticuloendothelial func-tion ³ ), and the imaging characteristics of various modalities, notably MR imaging, CT, sonography, and scintigraphy. Each of these modalities offer different advantages for the detection and characterization of FNH. In many cases, it is possible to obtain a prospective imaging diagnosis of FNH; however, in some cases, the distinction between FNH and other primary hepatic neoplasms is not possible. In these latter cases, close imaging follow-up, needle biopsy, or surgical resection may be necessary.

Since FNH lesions contain sufficient number of Kupper cells, these tumors usually concentrate or hyperconcentrate sulfur colloid. Thus, in the majority of cases they appear indistinguishable from normal hepatic parenchyma on liver-spleen scans. On two-dimensional ultrasound, ⁴ the lesions are usually homogeneous and isoechoic, and the central scar is rarely depicted. Color Doppler ultrasound, however, shows rich vascularity, in 25% of cases the vessels demonstrate a stellate pattern. Doppler spectra show medium- to high-flow velocities. On unen-hanced CT scans, all the lesions appeared homogeneous and isodense; in 80% of cases, a central hypodense area corresponding to the scar is demonstrated clearly. On triple-phase dynamic CT scans, the peripheral parenchyma of these lesions demonstrate transient and marked hyperdensity, with a gradual return to isodensity of the normal hepatic tissue in the parenchymal and venous phases. Conversely, the central scar density is hypodense in the arterial phase and increases progressively in the later phases, ultimately reaching higher values than the surrounding lesion. On MR images, ⁴ the lesion appears isointense on T1-weighted images and isointense or slightly hyperintense on T2-weighted images. The central scar is hypointense on T1-weighted images and hyperintense on T2-weighted images.

Two-dimensional ultrasound alone has poor specificity. The addition of color Doppler increases sonographic specificity to 100%, but the combined ultrasound exam still has low sensitivity for FNH. Dynamic CT sensitivity has been reported as 80% and MRI sensitivity as 40%. ⁴ In another study, it was reported that the best imaging modality for the diagnosis of FNH was enhanced MRI, with a sensitivity of 70% and a specificity of 98%.

FNH without a central scar ⁶ and with intralesional bleeding has been reported. ⁷ In such cases, preoperative imaging diagnosis becomes impossible. In our case, intra-lesional necrosis and bleeding was probably secondary to the size of the lesion and to the lack of a central scar containing the large blood vessels.

In atypical cases such as this one, considerable overlaps can exist ⁸ in the appearance of various pathologic entities that occur in the liver, such as hepatic hemangioma, adenoma, FNH, intrahepatic cholangiocarcinoma, metastatic disease, hepatocellular carcinoma, regenerating nodules, adenomatous hyperplastic nodules, and abscess. Another study demonstrated that only a small number of patients with FNH (2 of 12 cases) have classic or typical triphasic helical CT manifestation. ⁹ In these cases, additional imaging studies, such as a Technitium 99m-sulfur colloid liver scan, an enhanced MR scan, or a percutaneous biopsy, may be crucial for correct diagnosis.

In summary, it is important for radiologists to be aware of the uncommon appearance of liver FNH including, in this case, lack of a central scar and the presence of cystic areas. Familiarity with these varied CT and MRI imaging features will permit a more accurate diagnosis and prevent a false diagnosis.

REFERENCES

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Prepared by Feng Tao, MD, Department of Radiology, and Frank Bieuei, MD, Department of Pathology, Lenox Hill Hospital, New York, NY; and Richard A. Heiden, MD, Department of Radiology, Interfaith Medical Center, Brooklyn, NY.