Giant focal nodular hyperplasia with atypical imaging due to absent central scar: A case report

Abstract

Focal nodular hyperplasia (FNH) is widely recognized as one of the leading benign hepatic neoplasms encountered in clinical practice, disproportionately affecting women during their third through fifth decades of life. Although generally asymptomatic, FNH may occasionally present with acute abdominal pain, as illustrated in our case of a young woman with symptomatic giant FNH. Ultrasound, computed tomography, and MRI constitute the main imaging modalities used in the diagnostic evaluation of FNH, each contributing complementary information; however, distinguishing it from malignant hepatic tumors may remain challenging, particularly in atypical presentations. Histopathological examination may therefore be required to establish a definitive diagnosis. Herein we describe the case of a young woman aged 24 years who was referred to our institution following an acute episode of abdominal pain, in whom imaging revealed a large left hepatic lobe FNH with atypical radiological features, notably the absence of a central scar. Histological analysis confirmed the diagnosis. Due to the extrinsic compression effect attributable to the lesion and associated signs of portal hypertension, liver transplantation was considered. This case highlights the importance of recognizing the variable clinical and radiological manifestations of FNH and discusses the diagnostic and therapeutic challenges associated with atypical giant lesions.

Introduction

Focal nodular hyperplasia (FNH) is the second most common benign liver tumor after hemangioma, with an estimated prevalence of 0.9% and a marked predilection for women in their third to fifth decades [1]. It represents a hyperplastic hepatocellular response rather than a true neoplasm and is usually asymptomatic, being increasingly detected incidentally on imaging, which allows confident noninvasive characterization in up to 80% of cases.

We describe an unusual case of giant, symptomatic FNH in a young woman. Its educational value lies not in the absence of a radiologically visible central scar alone, but in the combination of a giant symptomatic lesion, markedly atypical imaging features, histological confirmation despite this imaging discordance, and clinically significant compressive complications that prompted multidisciplinary consideration of liver transplantation.

Case report

We report the case of a 24-year-old female with no significant medical history and no identifiable risk factors, particularly no history of oral contraceptive use, who attended the emergency department complaining of acute abdominal pain alongside vomiting, persisting despite several courses of symptomatic treatment.

The abdominal pain was localized to the right hypochondrium without irradiation. Physical examination disclosed no fever, and the patient reported no constitutional symptoms.

On admission, all vital signs were stable. Physical assessment revealed tenderness in the right upper quadrant associated with hepatomegaly. Laboratory investigations, including a complete blood count with platelet count, liver function tests, coagulation profile, and tumor markers, were performed and are summarised in Table 1. Aside from a slight elevation in alkaline phosphatase at 112 U/L (normal range: 36-108 U/L), all parameters were within normal limits; in particular, the platelet count showed no evidence of thrombocytopenia despite the splenomegaly subsequently noted on imaging, and the coagulation profile and albumin level confirmed preserved hepatic synthetic function.

Table 1.

Summary of laboratory investigations.

Category	Test	Result	Reference range
Complete blood count	Hemoglobin	13	12-15.5 g/dL
	Platelet count	286 × 109 (no thrombocytopenia)	150-450 × 10⁹/L
Liver function tests	AST	21	10-40 U/L
	ALT	16	7-56 U/L
	Alkaline phosphatase	112 U/L (elevated)	36-108 U/L
	GGT	Normal	9-48 U/L
	Total bilirubin	Normal	0.3-1.2 mg/dL
Coagulation profile	PT/INR	Normal	INR 0.8-1.1
Synthetic function	Albumin	Normal	3.5-5.0 g/dL
Tumor markers	—	Normal	—

Abdominal ultrasound demonstrated a large homogeneous iso-echoic hepatic lesion without a visible central scar. Color Doppler ultrasound did not reveal significant intralesional vascular flow.

Computed tomography (CT) revealed a left hepatic lobe mass that was isodense relative to the adjacent liver parenchyma on unenhanced images. Following contrast administration, the lesion showed intense diffuse arterial hyperenhancement followed by isoattenuation to the surrounding liver parenchyma in the portal venous phase (Fig. 1). Splenomegaly was evident on the same examination, with a craniocaudal splenic diameter of 14 cm, without compression or narrowing of the main portal vein; a dedicated Doppler ultrasound assessment of the portal venous system was not performed.

Fig. 1.

CT scan demonstrating a left hepatic lobe mass that was isodense relative to the liver parenchyma before contrast administration (orange arrow) (A). Following contrast injection, the lesion showed intense homogeneous diffuse arterial phase hyperenhancement (yellow arrows) (B) followed by equalization of attenuation to the adjacent hepatic parenchyma on portal venous phase sequences (yellow arrow) (C).

MRI evaluation identified a well-delineated lesion occupying the left hepatic lobe and measuring 100 × 80 mm in its greatest dimensions, demonstrating T1 isointensity relative to the adjacent liver and subtle T2 hyperintensity.

Dynamic gadolinium-enhanced sequences demonstrated early homogeneous arterial enhancement lacking washout appearance on portal venous phase sequences. No central scar was visualized throughout the examination (Fig. 2). Hepatobiliary-phase imaging with a hepatocyte-specific contrast agent was not performed.

Fig. 2.

Magnetic resonance imaging demonstrating a solitary hepatic lesion (yellow star), demonstrating subtle T2 hyperintensity (A) with preserved isointensity on non-contrast T1-weighted acquisitions (B). Dynamic contrast-enhanced sequences demonstrated early homogeneous arterial enhancement (C), without portal venous washout or visualization of a central scar. Diffusion-weighted imaging (D) showed no evidence of restricted diffusion within the lesion.

Because of the atypical radiological appearance, notably the absence of a central scar, histopathological examination was performed and confirmed the diagnosis of focal nodular hyperplasia (Fig. 3).

Fig. 3.

Histological section stained with hematoxylin and eosin under low-power magnification demonstrates microscopic fibrous septa with scar-like features characteristic of focal nodular hyperplasia, containing malformed bile ductules and thick-walled aberrant vessels, and delineating hyperplastic hepatocytes devoid of cytologic atypia. These microscopic findings, while consistent with the fibrous architecture typically associated with the central scar of FNH, were too dispersed and architecturally subtle to produce a macroscopically visible central scar on any imaging modality.

The patient was discussed in a multidisciplinary tumor board, where surgical management options, including liver transplantation, were considered because of the lesion's size and compressive effects. Following this discussion, the patient was lost to follow-up before a definitive management decision could be implemented, and no follow-up imaging was subsequently available to assess lesion stability or evolution.

Discussion

Ranking second among benign hepatic tumors after hemangioma [2], FNH predominantly arises within the right hepatic lobe [3]—making the left-lobe location of our lesion a further atypical feature of this case.

The pathogenesis of FNH is not fully understood [4]. Although exogenous estrogen through oral contraception and intrinsic hormonal stimulation have historically been implicated in lesion pathogenesis, this association has not been definitively established [5]. Current evidence points toward a vascular anomaly triggering alterations in angiopoietin gene expression as the most likely underlying mechanism [4].

The vast majority of FNH cases are clinically silent and discovered incidentally [4]. When symptomatic, larger lesions may cause nonspecific abdominal discomfort, early satiety, or a palpable mass through extrinsic compression of adjacent structures [5]. FNH is typically well-demarcated and nonencapsulated, most commonly measuring 4-8 cm, although lesions up to 20 cm have been reported [6,7].

The hallmark macroscopic feature of FNH is a central stellate fibrovascular zone, which has been described in the literature under several designations, including “central scar,” “fibrous scar,” and “scar-like fibrosis” [8]. This structure is histologically characterized by a dense collagenous stroma traversed by numerous vascular channels. Among these, intermediate- and large-diameter arteries with thickened walls are especially conspicuous, often displaying fibromuscular proliferation, intimal smooth muscle cell overgrowth, and mucoid degenerative changes, with varying extents of luminal stenosis [8]. In our case, while these histological hallmarks were confirmed on pathological examination, no macroscopic central scar was identifiable on any imaging modality, illustrating that the absence of this feature on imaging does not preclude its microscopic existence and should not exclude the diagnosis of FNH.

Sonographic characterization of FNH has limited sensitivity [6,9]; the lesion typically appears as a sharply marginated, homogeneous, isoechoic mass, occasionally with a hypoechoic peripheral halo or a central echogenic focus [10]. Color Doppler may reveal a central feeding artery with a radial “spoke-wheel” pattern of branching vessels within the fibrous septa [11,12].

On unenhanced CT, the lesion classically exhibits a scalloped border [10] with hypo- or isoattenuation compared to the background liver parenchyma, the central stellate scar being visualized in nearly one-third of cases [5]. Following contrast administration, it demonstrates intense arterial enhancement and becomes isoattenuating during the portal venous phase [13].

Among available imaging techniques, MRI stands as the preferred modality for the characterization of FNH and its distinction from hepatocellular adenoma [14]. On MRI, FNH characteristically demonstrates iso- or hypo-intensity on T1-weighted sequences and iso- or mild hyperintensity on T2-weighted sequences. The near-isointensity observed on pre-injection sequences reflects the existence of structurally preserved hepatocytes and constitutes a key discriminating feature from other focal hepatic lesions [10].

The differential diagnosis of a hypervascular hepatic mass lacking a definite central scar should include hepatocellular adenoma, conventional and fibrolamellar hepatocellular carcinoma (HCC), and hypervascular metastases, as summarised in Table 3. Hepatocellular adenoma typically occurs in young women, often with a history of oral contraceptive use, and shows homogeneous arterial enhancement similar to FNH; however, unlike FNH, most adenomas fail to retain hepatobiliary-specific contrast agents and appear hypointense relative to liver on the hepatobiliary phase—a distinction that could not be applied in our case owing to the absence of this sequence [15,16]. Conventional HCC, particularly in a cirrhotic liver, typically shows arterial hyperenhancement with washout on the portal venous or delayed phase, a pattern not observed in our patient, although atypical HCCs may occasionally mimic FNH on the hepatobiliary phase [15]. Fibrolamellar HCC characteristically arises in young patients without underlying liver disease and may also contain a central scar; however, this scar is typically hypointense on both T1- and T2-weighted sequences, in contrast to the T2-hyperintense scar of FNH, and calcification—rare in FNH—is common [17]. Hypervascular metastases usually show washout on delayed-phase imaging and occur in the context of a known primary malignancy, which was absent in our patient.

Table 3.

Key imaging features differentiating FNH from its principal hypervascular mimics.

Feature	FNH (our case)	Hepatocellular adenoma	Conventional HCC	Fibrolamellar HCC	Hypervascular metastases
Typical patient	Young–middle-aged women	Young women, oral contraceptive use	Older patients, cirrhosis/chronic liver disease	Young patients, no underlying liver disease	Known primary malignancy
Arterial phase	Homogeneous hyperenhancement	Homogeneous hyperenhancement	Hyperenhancement (may be heterogeneous)	Heterogeneous hyperenhancement	Hyperenhancement
Portal venous/delayed phase	Isoattenuating, no washout	May show washout	Washout (LI-RADS pattern)	Iso- to hypo-attenuating	Washout
Central scar	Present in up to one-third; T2-hyperintense	Usually absent	Absent	Present; hypointense on T1 and T2	Absent
Hepatobiliary phase	Iso-/hyperintense (retained)	Typically hypointense (most subtypes)	Typically hypointense	Hypointense	Hypointense
Calcification	Rare	Rare (except lipid-rich subtype)	Occasional	Common	Variable

As illustrated in Table 2, our case shares several features with previously reported cases of giant or atypical FNH, while retaining a number of distinctive characteristics. From an imaging standpoint, the complete absence of a central scar across all 3 modalities—ultrasound, CT, and MRI—represents the most defining and challenging aspect of our observation. This feature has been previously reported in the series described by Matsushita et al. [18] and Singh et al. [2], both involving lesions of comparable size in segment 4 of the left lobe [2,18]; however, in those reports, the absence extended to histopathological examination as well [2,18]. Our case differs in that microscopic fibrous septa with typical FNH composition remained identifiable on histology despite the absence of any macroscopic imaging correlate, supporting the hypothesis that in giant FNH, the central scar may be too architecturally dispersed to be resolved by conventional imaging. Several mechanisms may explain this radiologic-pathologic discordance. In giant lesions, the fibrovascular network typical of the central scar may be distributed across multiple smaller septa rather than concentrated within a single dominant zone, falling below the spatial and contrast resolution achievable with conventional cross-sectional imaging even when clearly identifiable microscopically. Atypical vascular remodelling within the scar itself, such as a predominance of dilated, low-flow vessels rather than the classic thick-walled feeding arteries, has also been reported to produce an atypical enhancement pattern that can render an otherwise histologically evident scar inconspicuous on dynamic imaging [19,20]. Finally, as a considerable proportion of FNH lesions fail to demonstrate a visible scar even at conventional size [5], this inherent limitation of ultrasound, CT, and MRI alike would be expected to be compounded, rather than mitigated, by the disproportionate growth of a giant lesion. The case of Yoon et al. [21] represents the closest parallel in this regard, with histological confirmation of FNH in the absence of a visible central scar on MRI, although in considerably smaller lesions [21]. Beyond the imaging atypicality, the compressive mass effect and associated splenomegaly—without portal vein compression—prompted multidisciplinary discussion of liver transplantation—a management consideration that, to our knowledge, remains exceptionally rare in the setting of FNH without an underlying vascular disorder.

Table 2.

Comparison of our case with selected published cases of giant and/or atypical FNH without central scar on imaging.

Study	Age/sex	Size	Symptoms	Central scar (imaging)	Central scar (histology)	Management
Our case	24 F	100 × 80 mm	RUQ pain, nausea, and hepatomegaly	Absent (US, CT, and MRI)	Present (fibrous septa, aberrant vessels, and bile ductules)	MDT; surgery/transplantation discussed
Matsushita et al. [18]	31 M	100 mm (segment 4)	Hepatic mass evaluation	Absent (no scar and no spoke-wheel pattern)	Absent (no stellate scar on 1-cm sections)	Extended left lobectomy
Singh et al. [2]	48 F	110 mm (segment 4)	Upper abdominal pain (1 y)	Absent (US and CT)	Absent (gross specimen)	Left lobectomy
Yoon et al. [21]	Not specified (2 cases)	Not specified	Not specified	Absent on MRI (mimicking HCC)	FNH confirmed histologically	Histological diagnosis; no resection
Eris et al. [22]	23 F	Large (compressive)	Nausea, vomiting, abdominal pain; gastric outlet obstruction	Not specified	FNH confirmed histopathologically	Surgical resection; complete symptom resolution

Values in bold indicate the characteristics of the present case.

Given the benign nature of FNH and the risks associated with invasive procedures, conservative management is generally favoured; periodic imaging follow-up, typically at 3- to 6-month intervals initially, has been suggested for indeterminate or growing lesions, although the optimal interval has not been formally established [10]. However, biopsy or surgical management may be indicated in symptomatic patients, in cases of diagnostic uncertainty, or when progressive lesion enlargement is observed. Surgical resection remains the definitive treatment for symptomatic lesions.

Conclusion

Giant FNH remains an uncommon presentation of a common benign liver lesion. In the absence of typical imaging findings, particularly a central scar, and without hepatobiliary-phase characterization, differentiation from malignant hepatic tumors may be challenging and histopathological confirmation may be required. This case also illustrates that exceptionally large lesions may produce clinically significant compressive complications, requiring multidisciplinary evaluation and individualized management strategies.

Ethical approval

No ethical approval was required for this article.

Patient consent

Written informed consent was obtained from the patient for the anonymized information to be published in this article.