Rare benign liver tumors that require differentiation from hepatocellular carcinoma: focus on diagnosis and treatment

Recently, an increase in the number of asymptomatic rare benign liver tumors (BLTs) has been reported during health check-ups. It is difficult to determine the nature of partial rare BLTs and not easy to distinguish from malignant liver tumors. This study aimed to analysis clinical features, diagnosis and treatment of rare BLTs to reduce misdiagnosis and provide reference for clinical practice. From January 2012 to January 2021, we treated 112 rare BLTs by hepatectomy, including 54 focal nodular hyperplasias, 14 hepatocellular adenomas, 28 hepatic angiomyolipomas, 3 hepatic granulomas, 2 inflammatory pseudotumors of the liver, 2 nodular regenerative hyperplasia, 2 hepatic lipomas, 1 solitary fibrous tumor of the liver, 1 hepatic schwannoma and 1 hepatic myelolipoma. The majority of patients were middle-aged female and asymptomatic. Single tumors were dominant. The diagnostic accuracies of computed tomography (CT) and magnetic resonance imaging (MRI) were 32.5% and 44.2%, respectively. The majority of tumors were likely to be misdiagnosed as hepatocellular carcinoma (HCC) or difficult to distinguish from HCC. All patients underwent surgical treatment. Postoperative pathological and immunohistochemical examination can confirm the diagnosis. No patients without tumor recurrence or metastasis during follow-up period. Altogether, the clinical symptoms of rare BLTs lack specificity, and their preoperative diagnosis largely depends on imaging examination, with a low diagnostic accuracy rate and high chances of misdiagnosis as HCC. Diagnosis is confirmed by pathological and immunohistochemical examination. Surgical resection for rare BLT is safe and effective, regular postoperative follow-up is necessary.


Introduction
With the development of medical imaging technology and increased health awareness of residents, an increasing number of asymptomatic benign liver tumors (BLTs) are being discovered incidentally. BLTs are diversified lesions involving different cell origins; these can be divided into regenerative lesions and neoplastic lesions (Zimmermann 2001). The most common regenerative lesions are hepatic hemangioma and focal nodular hyperplasia (FNH), whereas neoplastic lesions include hepatocellular adenomas (HCA) and hepatic angiomyolipomas (HAML) (Belghiti et al. 2014). Regenerative lesions generally do not require treatment because their volume rarely changes significantly over time (Chiche and Adam 2013). Although true neoplastic lesions are associated Laihui Luo, Tao Wang and Mengting Cheng contributed equally to this study. with complications (malignant transformation or bleeding), a better understanding of the growth process and radiological and pathological features has reduced the number of cases diagnosed by invasive methods and resection (Cho 2016;Nault et al. 2013;Thevathasan et al. 2021). However, it is difficult to determine the nature of rare benign liver tumors, especially to distinguish them from malignant liver tumors. Therefore, timely clinical intervention is required (European Association for the Study of the 2016; Marrero et al. 2014).
At present, therapeutic indications of rare BLTs have remained controversial (Margonis et al. 2015;Perrakis et al. 2017). In contrast, improper overtreatment increases the economic burden, and can even endanger the health and life of patients. For BLTs associated with the risk of malignant transformation, blind conservative observation could delay the optimal treatment time, resulting in serious consequences.
Here, we report a series of 112 rare BLT patients. We investigated the clinical characteristics, imaging, and pathological features of different types of rare BLTs, which can deepen the understanding of rare BLTs and improve the level of diagnosis and treatment.
Excised tumoral specimens were fixed in formalin and embedded in paraffin. Next, the specimens were stained with hematoxylin-eosin and histologically examined, and immunohistochemical examination was performed on other sections.

General information
The characteristics of 112 patients are shown in Table 1. The study participants include more number of women (66/112). The mean age of patients was 40.4 years (range: 18-74 years). Three women had a history of oral contraceptives. Seven patients had a chronic disease, 1 HAML patient with renal AML, and 1 NRH patient with portal hypertension. Forty-one patients showed clinical symptoms, the most common of which were abdominal pain and distension (34/41). The tumor volume increased significantly in two patients during follow-up, abdominal distension accompanied by nausea and vomiting in two patients, abdominal distension accompanied by decreased appetite in 1 patient, and mental tension in 1 patient. The longest duration of symptoms was more than 5 years.
We did not observe abnormality in routine blood tests and coagulation functions in all patients. Liver function was classified as Child-Pugh A for 110 cases, and Child-Pugh B for two patients. There were 14 patients with abnormal tumor markers, including eight patients with abnormal AFP elevation (range: 7.53-15.09 ng/mL, normal: 0-7 ng/mL) and six patients with abnormal CA 19-9 elevation (range: 27.21-76.03 U/mL, normal: 0-27 U/mL), all of which were slightly elevated. Seventeen patients were positive for HBsAg.

Imaging examinations
Computed tomography (CT) and/or magnetic resonance imaging (MRI) examinations were performed in all patients. There were 103 cases of a single tumor, 8 cases with two tumors, and 1 case with three tumors. The distribution of tumor was as follows: left lobe (n = 41), right lobe (n = 59), caudate lobe (n = 6), left and right lobes (n = 6). The tumor diameter ranged from 1.3 to 21.3 cm, with an average of 5.3 ± 3.7 cm. Among the 112 patients, 77 patients underwent CT examination, 77 patients underwent MRI examination (including 26 Gd-EOB-DTPA MRI), and 32 patients underwent two imaging examinations.
We analyzed the CT and MRI features of 58 FNHs and 28 HAMLs (Tables 3 and 4). Although certain tumors had characteristic imaging findings (central scar shadow in FNH, intra-tumoral dysmorphic vascular, and early venous drainage in HAML), most tumors displayed a wide spectrum of imaging findings, especially in the arterial enhancement phase and portal vein phase. The diversity of imaging findings undoubtedly made the diagnosis difficult.

Histopathological and immunohistochemical characteristics
All 112 surgical specimens underwent pathological examination, 91 of whom underwent immunohistochemical examination (Table 5 shows the antibody expression of FNH, HCA, and HAML).
Most tumor types showed typical pathological and immunohistochemical features. For example, certain tumors with fat components included HAML, hepatic lipoma, and myelolipoma; these tumors were hypo-vascular. HAML ( Fig. 1) was composed of abnormal blood vessels, smooth muscles, and mature fat cells in different proportions, accompanied by a few inflammatory cells. Hepatic lipoma was composed entirely of mature adipose tissue. Hepatic myelolipoma consisted of mature adipose tissue and hematopoietic elements, containing erythroid cells and myeloid cells (Fig. 2).
Microscopically, SFTL was composed of spindle cells and interspersed collagen, high cellular proliferation of spindle cells arranged in a storiform pattern, with the immunohistochemical staining profile of CD34 ( +), vimentin (3+), Bcl-2 (+), and SMA (−). The hepatic schwannoma ( Fig. 3) was composed of Antoni A and Antoni B areas. The Antoni A area was a hypercellular area, containing numerous closely staggered bundles of fusiform Schwann cells. The Antoni B area was a loose myxoid structure composed of colloidal microcapsules with a few sparse cells. Immunohistochemistry showed that hepatic schwannoma was positive for S-100 and CD56.
The expression of immunohistochemical stains with related antibodies could be well identified as FNH, HCA, and HAML (Table 5). HAMLs showed 100% positive expression of an anti-HMB-45 antibody, whereas the expression of Melan-A, Vimentin, and SMA was over 80%. Unlike HCA, CK19 and CK7 were highly expressed in proliferous small bile ducts in FNHs. Although hepatocytes, CD34, and GS were highly expressed in HCA and FNH, different staining patterns could distinguish the two types of tumors.

Follow-up
Postoperative follow-up included returning outpatient and telephone follow-up. The follow-up period was 3 to 102 months, and 17 patients were lost to follow-up. During the follow-up, two patients died of natural causes. The other patients were all alive without tumor recurrence or metastasis.

Discussion
The development and progression of imageology have greatly reduced the incidence of puncture biopsy and surgical resection. In addition, conservative treatment is being used for a better understanding of the natural history, biological, radiology and pathological characteristics of rare BLTs. However, clinical symptoms of certain patients were evident, the nature of the tumor was unclear and difficult to distinguish from the malignant tumor or there was a risk  of complications. Therefore, timely clinical intervention is highly necessary (Mezhir et al. 2013). Diagnosis plays an important role in rare BLTs because it is related to the choice of follow-up treatment (Oldhafer et al. 2020). The diagnosis of rare BLTs is based on detailed medical history, physical examination, imaging and pathological examinations (Marrero et al. 2014). The diagnostic process is based on differentiating from various malignant tumors.
The background of underlying liver disease (cirrhosis and steatosis) will make the diagnosis of the lesion difficult (Costa et al. 2018). In this group, eight patients showed mildly abnormal elevation of AFP, three of them were positive for hepatitis B and misdiagnosed as HCC on imaging. These factors would lead to misdiagnosis. Female take of oral contraceptives could be an important reference for the diagnosis of HCC (Giannitrapani et al. 2006). Most patients with rare BLTs are asymptomatic, and a small number of patients have non-specific gastrointestinal symptoms, such as abdominal pain, distention, loss of appetite and nausea. Jaundice, intra-tumoral infection, spontaneous or traumatic rupture bleeding are rare.
Radiology examination plays an essential role in the evaluation of rare BLTs. Ultrasound is the most commonly used screening procedure. Enhanced CT or MRI examination is a significant diagnostic and classifying method for rare BLTs, which can comprehensively understand the lesions and clarify the nature of lesions.
In this group of cases, the accuracy of imaging diagnosis was low, several patients were misdiagnosed as HCC or difficult to distinguish from well-differentiated HCC. Reasons for the above problems included (1) most rare BLTs lacked characteristic imaging findings, (2) rare BLTs exhibited a wide spectrum of imaging findings, benign and malignant  lesions were even intersected, (3) radiographic diagnosis was not combined with the background of underlying liver disease and laboratory examinations, with the possibility that diagnosis could be misled by medical history, (4) the rarity of the tumor makes it poor to understand and difficult for radiologists to accurately diagnose it, and (5) inherent pitfalls in liver imaging. Related studies have reported that Gadoxetic acid MRI is helpful in the diagnosis and differential diagnosis of liver tumors (Motosugi et al. 2010;Suh et al. 2015). This research also showed the advantages of Gadoxetic acid MRI. In our study, 26 cases underwent Gadoxetic acid MRI examination with a diagnostic accuracy of 76.9%. Compared with conventional screening, Gadoxetic acidenhanced hepatocyte-phase MR imaging can better define the nature of the lesion. The literature reports that hepatobiliary MR contrast agents can be used to highlight the hepatocellular origin of lesions, the sensitivity and specificity to differentiate FNH from HCA with GD-BOPTA or gadoxetic acid MRI ranges from 92 to 96.9% and 91 to 100%, respectively (Grazioli et al. 2012;McInnes et al. 2015). When imaging studies are inconclusive, a biopsy is used to confirm the diagnosis. However, liver biopsy is an invasive method and associated with complications including pain and bleeding; therefore, a liver biopsy may not be appropriate in certain cases.
The correct diagnosis depends on pathology and immunohistochemistry. Immunohistochemistry showed characteristic antibodies that could better identify the tumors and confirm the histological diagnosis. Our pathological examination was consistent with the features reported in the literature. For example, the positive expression of HMB-45, Melan-A, and SMA are the primary immunomarkers and reliable diagnostic evidence for HAMLs . Two distinct cellular regions (Antoni A and Antoni B areas) of the hepatic schwannoma and antibody S-100 positivity, CD34 and CD117 negativity (Picchia et al. 2019;Wan et al. 2016). Hematopoietic components of hepatic myelolipomas, like erythroid, megakaryocytes and myeloid colonies. (Radhi 2010). Microscopically, IPT (Fig. 4) is characterized by fibroblastic proliferation and chronic inflammatory cell infiltration (Yang et al. 2015). Immunohistochemical stains with antibodies to CD34, CK7, CK19 and GS can differentiate between FNH and HCA (Bioulac-Sage et al. 2007). In this group of tumors, the low expression of malignant tumor immunohistochemical biomarkers such as GPC3, GS and HSP70 can enable us to distinguish HCC (Nguyen et al. 2016). These characteristic histological findings and immunohistochemical staining are of great significance for the diagnosis and differential diagnosis of lesions.
The treatment of rare BLTs depends on the presence or absence of symptoms and the possibility of malignancy, as well as the presence or absence of complications. Regular imaging follow-up is feasible for the majority of rare BLTs with a definite diagnosis and no risk of malignant transformation.
Unlike FNH, HCA has the potential risk of bleeding and malignant transformation (Bioulac-Sage et al. 2009). The size of HCA (5 cm) is associated with the risk of complications, and β-HCA has the highest risk of transition to HCC and has a male predominance. In addition, tumor rupture, hemorrhage, and malignant transformation of HAMLs have been reported (Garoufalia et al. 2018;Klompenhouwer et al. 2020). Although the majority of patients with SFTL have benign tumors, some may have malignant features, including recurrence and metastatic (Chen and Slater 2017). Fortunately, pathological examination revealed no malignant areas, and long-term follow-up showed no recurrence or metastasis in this group. Although surgical indications for rare BLTs are still controversial, they can be summarized as follows based on the guidelines and clinical practice (Hoffmann et al. 2015): (1) the presence of clinical symptoms associated with tumor, seriously affecting the quality of life, such as NRH present portal hypertension, jaundice from tumor compression, and dislodging other organs, cholestasis, compression of vessels; (2) the diagnosis is unclear, difficult to differentiate with malignant tumor; (3) tumors have the tendency of malignant transformation or certain special biological and histopathological features; (4) during the follow-up period, the tumor increased rapidly (> 2 cm per year) with risk of rupture and bleeding, or the tumor location was such that its growth could not be controlled. Fig. 1 (Hepatic angiomyolipoma). A 44-year-old female presented with a 6.9 × 3.9 cm mass in the right lobe of the liver with clear margin. The lesion showed homogeneous signals with slightly hypointense signal on T1WI and hyper-intense signal on T2WI (a, b). During the arterial and portal phase, showed progressive enhancement (c, d). H&E staining images (e magnification × 100; f magnification × 200) demonstrated that the hepatic angiomyolipoma mainly consisted of three components: dilated thick-walled vessels; epithelioid cells and mature lipid tissue. Immunohistochemistry demonstrated the cells were positive for HMB-45 (g magnification × 100), Melan A (h magnification × 100) In this study, the majority of patients underwent surgical treatment because of an unclear diagnosis or misdiagnosis as HCC. A few patients had their tumors resected because the clinical symptoms affected their daily life. Considering the risk of malignant transformation, we adopted an aggressive treatment strategy for HCA and HAML. During the operation, a rapid frozen pathological examination can be conducted first to determine benign and malignant lesions. For benign lesions, the scope of liver resection can be correspondingly reduced, whereas partial liver resection is dominant, and normal liver tissue should be preserved as far as possible. In the experienced liver surgery centers, laparoscopic hepatectomy is recommended to reduce surgical trauma and shorten hospital stays. Surgical resection is safe and effective to treat rare BLTs. Considering the risk of recurrence and metastasis of certain tumors, regular followup is necessary. Fig. 2 (Hepatic myelolipoma). An oval mass size of approximately 9.9 × 9.1 cm was observed in the right lobe of the liver of a 20-years-old female. MRI plain scan showed a mixed signal on the T1-weighted fat compression sequence and T2WI, necrotic tissue shadows could be seen in the tumor (a, b). DWI showed hyper-intense (c). During the arterial phase, heterogeneous enhancement and internal septa were observed (d). The degree of enhancement of lesion was decreased in portal stage and delayed stage (e, f). H&E staining images (g magnification × 100; h magnification × 200) demonstrated that hepatic myelolipoma had a clear boundary with normal liver tissue. The tumor was composed of mature adipocytes and hematopoietic tissue

Conclusion
To summarize, rare BLTs are diversified lesions involving different cell origins. Clinical symptoms of tumors lack specificity, and preoperative diagnosis mostly depends on imaging examination, with a low diagnostic accuracy rate and most easily misdiagnosed as HCC. The pathological and immunohistochemical examination can confirm the diagnosis. Individual treatment choices should be made according to patients specific conditions. Surgical resection for rare BLT is safe and effective, and regular postoperative follow-up is necessary. Availability of data and materials Original data are available per request.

Conflict of interest
The authors declare that they have no competing interest.
Ethics approval and consent to participate This retrospective study was conducted in accordance with the Declaration of Helsinki, and approved by the Institutional Review Board of the First Affiliated Hospital of Nanchang University, and the requirement for informed consent was waived.
Consent for publication Not applicable.