Segmental Atrophy of the Liver: A Distinctive Pseudotumor of the Liver With Variable Histologic Appearances Aatur D. Singhi, MD,* Hala R. Maklouf, MD, PhD,w Anupamjit K. Mehrotra, MD,z Zachary D. Goodman, MD, PhD,z Uta Drebber, MD,y Hans P. Dienes, MD,y and Michael Torbenson, MD* Abstract: Segmental atrophy of the liver can lead to the formation of a pseudotumor that can pose a diagnostic challenge. To better understand the full clinicopathologic spectrum of this pseudotumor, 18 cases were studied. Ages at presentation ranged from 14 to 91 years (median, 63 y) with a modest female-patient predominance (13 of 18, 72%). Upper right quadrant abdominal pain was the most common clinical presentation (14 of 18, 78%), and all the cases were mass lesions. The majority of cases were subcapsular (15 of 18, 83%) and ranged in size from 1.8 to 10.0 cm. All the cases contained abnormally thick-walled and often thrombosed vessels, with both arteries and veins affected. Biliary cysts were a common finding (7 of 18, 39%). Examination of the entire series of cases suggested a sequence of changes, with early lesions (n = 4) composed of collapsed hepatic parenchyma with preservation of portal areas, occasional islands of residual hepatocytes, and brisk bile ductular proliferation. These cases showed very mild elastosis. Other cases (n = 10) showed little or no ductular proliferation but had increased levels of elastosis. More advanced lesions (n = 3) were composed almost solely of elastosis with small scattered islands of unremarkable hepato- cytes, whereas an end-stage lesion (n = 1) was a discrete nodule of fibrosis. In conclusion, segmental atrophy of the liver is typically subcapsular, and is strongly associated with vascular injury. The lesion has multiple stages ranging from parenchymal collapse, to nodular elastosis, to nodular fibrosis. Recognizing the various morphologies will aid in proper diagnosis. Key Words: elastosis, liver, pseudotumor (Am J Surg Pathol 2011;35:364–371) B enign pseudotumors of the liver can present clinically and radiographically as neoplasms and can at times be diagnostically challenging. Segmental atrophy of the liver can lead to the formation of a pseudotumor that can present as a mass lesion and can have a variety of morphologic appearances. The morphologic variation can lead to diagnostic challenges for this rare psueudo- tumor, challenges further compounded by the incomplete description of this lesion in the literature. In this study, we examined the clinicopathologic spectrum of this rare pseudotumor. MATERIALS AND METHODS Cases Eighteen cases were collected from the surgical pathology files of 3 different institutions. All surgical pathology slides including special stains were reviewed and assessed for the extent of elastosis, associated vasculature changes, biliary cysts, bile ductular prolifera- tion, residual hepatocytes and portal tracts, and amount of inflammation. Demographic and clinical information were collected. Special Stains and Immunohistochemistry In most cases, histochemical stains were available from when the specimen was originally examined for diagnostic purposes. These stains included Verhoeff-van Gieson, Miller elastic, reticulin, Masson trichrome, and Movat pentachrome stains. Stains were performed on 4 to 5 m sections from formalin-fixed, paraffin-embedded tissue samples. Immunohistochemical staining for vimentin was also performed on a representative case from the nodular elastosis stage using 5 m sections from formalin-fixed, paraffin-embedded tissue sections. The slides were depar- affinized and subjected to antigen retrieval using 10 mM citrate buffer (921C for 30 min). The tissue sections were incubated with a mouse monoclonal antibody against vimentin (Ventana Medical Systems) at a 1:100 dilution. Immunostaining was visualized using the Ventana XT autostainer using a 1-view secondary detection kit (Ventana Medical Systems). Copyright r 2011 by Lippincott Williams & Wilkins From the *Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD; wDepartment of Gastrointest- inal and Hepatic Pathology, Armed Forces Institute of Pathology, Washington, DC; zDepartment of Pathology, Inova Fairfax Hospital, Falls Church, VA; and yDepartment of Pathology, Institute of Pathology, University Hospital Cologne, Cologne, Germany. Correspondence: Michael Torbenson, MD, The Johns Hopkins Uni- versity School of Medicine, 1503 E. Jefferson, Rm. B314, Baltimore, MD 21231 (e-mail: mtorben@jhmi.edu). ORIGINAL ARTICLE 364 | www.ajsp.com Am J Surg Pathol  Volume 35, Number 3, March 2011