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A 52-year-old male presented to our hospital with a focal hepatic mass that was incidentally detected on the screening ultrasound and computed tomography (CT). The patient did not have a relevant medical history or any related complaints. All levels of serum tumor markers, including alfa-fetoprotein, carcinoembryonic antigen, carbohydrate antigen 125, and carbohydrate antigen 19-9 were within normal limits.

Ultrasonography revealed a well-encapsulated, hypoechoic round lesion in the left lobe of the liver. On CT, a well-defined, hypoattenuating mass was indicated with enhancement of the capsule adjacent to the left portal vein (Fig. A). Positron emission tomography (PET) demonstrated increased 2-fluoro-2-deoxy-D-glucose (FDG) uptake in this lesion, suggesting a malignant tumor or inflammatory mass (Fig. B).

The patient underwent lateral segmentectomy, and a cross-section of surgical specimen showed a well-demarcated, yellowish, solid round mass measuring 3 cm × 4.5 cm with minimal myxoid component and capsulation (Fig. C). A microscopic specimen obtained at the junction of the tumor and the liver (arrowhead), consisting of densely packed spindle cells (arrow) surrounded by a capsule, was compatible with the findings of schwannoma (Fig. D). An immunohistochemical study was performed on the mass. The tumor cells, which showed a whorl pattern, were positive for immunochemical staining with S-100 protein (Fig. E). However, the tumor cells were negative for smooth muscle actin, c-kit, and CD34.

Hepatic schwannoma is a very rare benign mesenchymal tumor that originates from a variety of hepatic sympathetic and parasympathetic nerves distributed in the intralobular connective tissues along the portal veins.1, 2 The histologic hallmarks of a schwannoma are the presence of a true capsule and mixture of Antoni A (hypercellular area) and Antoni B (hypocellular area with a more myxoid matrix and water content) regions. This tumor usually presents as an encapsulated, homogeneous, hypo-enhancing mass located along the portal veins on CT scan. As the tumor becomes larger, however, it shows variable heterogeneity depending on secondary degeneration of cystic change, calcification, and hemorrhage formation. Visual qualitative assessment of FDG-PET images usually reveal high tumor-to-background ratios for schwannomas with high cellularity, which limits the utility of PET for distinguishing schwannomas from malignant tumors.3 Hepatic schwannomas should be differentiated from other primary mesenchymal tumors such as leiomyomas and gastrointestinal stromal tumors which are positive for muscle markers (actin/desmin) and c-kit, respectively, on immunohistochemical staining.

References

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  2. References
  • 1
    Lee WH, Kim TH, You SS, Choi SP, Min HJ, Kim HJ, et al. Benign schwannoma of the liver: a case report. J Korean Med Sci 2008; 23: 727730.
  • 2
    Park MK, Lee KT, Choi YS, Shin DH, Lee JY, Lee JK, et al. A case of benign schwannoma in the porta hepatis [in Korean]. Korean J Gastroenterol 2006; 47: 164167.
  • 3
    Beaulieu S, Rubin B, Djang D, Conrad E, Turcotte E, Eary JF. Positron emission tomography of schwannomas: emphasizing its potential in preoperative planning. AJR Am J Roentgenol 2004; 182: 971974.