Hepatic Superscan on [¹⁸F]-FDG Positron Emission Tomography/Computed Tomography

Abstract

Sarcoidosis is an idiopathic granulomatous disease most commonly involving the lungs; however, isolated extrapulmonary manifestations such as hepatic sarcoidosis are rare and diagnostically challenging. We describe a case of hepatic sarcoidosis in a 24-year-old man who presented with a three-month history of low-grade fever and unintentional weight loss. Clinical examination was unremarkable, and initial blood investigations revealed elevated alkaline phosphatase, lactate dehydrogenase, inflammatory markers, and serum ACE levels, with a negative work-up for tuberculosis and autoimmune diseases. Chest imaging was normal. [¹⁸F]-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) revealed diffuse hypermetabolic liver (hot liver) with reduced physiological uptake in the myocardium and kidneys, consistent with a hepatic superscan pattern. No significant pulmonary nodules or mediastinal/hilar nodal involvement was detected. In view of the hepatic superscan, a liver biopsy was suggested, which revealed hepatic sarcoidosis. The patient was diagnosed with ‘Hepatic sarcoidosis’ and responded well to corticosteroid therapy. This case highlights the importance of [¹⁸F] FDG PET/CT in guiding diagnosis in cases of unexplained systemic symptoms. The hepatic superscan appearance, typically associated with malignancy, can also be observed in rare granulomatous diseases such as sarcoidosis, reinforcing the need for histopathological confirmation. [¹⁸F] FDG PET/CT is also beneficial for a whole-body survey in detecting occult diseases and guiding further investigations, such as targeted biopsies.

 

MissingLinkText

Keywords

[¹⁸F]-FDG PET/CT - hepatic sarcoidosis - hepatic superscan - histopathology - infective etiology - infiltrative disorders

Introduction

Sarcoidosis is an idiopathic granulomatous disease that can affect any organ, most commonly the lungs. Extrapulmonary organ involvement occurs in up to 50% of patients, but only 5 to 9% of patients have extrapulmonary disease without pulmonary involvement: nonpulmonary sarcoidosis.[1] The hallmark of sarcoidosis is the formation of epithelioid granulomas that are typically noncaseating, and the pathogenesis of sarcoidosis is still not completely understood.[2] These cases often prove to be diagnostic dilemmas, requiring biochemical, imaging, and invasive testing to confirm the diagnosis of sarcoidosis.

 

MissingLinkText

Case Presentation

A 24-year-old gentleman presented with complaints of continuous low grade fever and unintentional weight loss for 3 months. He had no history of jaundice, no skin rashes, and no palpable lymphadenopathy. His abdomen was soft and nontender, with no organomegaly. Differential diagnosis considered were disseminated tuberculosis (TB), lymphoma, and autoimmune or infiltrative disorders.

Initial blood tests indicated normal liver function but showed elevated levels of alkaline phosphatase: 274 IU/L (normal range: 40–129 IU/L), lactate dehydrogenase: 596 IU/L (normal range: 135–214 IU/L), and inflammatory markers, including erythrocyte sedimentation rate: 43 mm/h (normal range: 1–13 mm/h), C-reactive protein: 146 mg/L (normal range: <5 mg/L), and angiotensin-converting enzyme (ACE): 131 IU/L (normal range: 20–70 IU/L). Comprehensive autoimmune work-up, including antinuclear antibody testing, was negative. Complement levels were within normal limits, with C3 of 115 mg/dL and C4 of 14.7 mg/dL, effectively ruling out active autoimmune or connective tissue disease. To rule out malignancy, serum α-fetoprotein and serum calcium tests were performed, with results falling within normal limits. Chest X-ray did not reveal any abnormalities. The work-up for TB, such as XPERT TB PCR and Mycobacterium culture, was also negative.

Considering the inconclusive laboratory findings, a whole body [¹⁸F]-FDG PET/CT was performed. [¹⁸F]-FDG PET/CT revealed diffusely increased hepatic uptake with a SUV_max of 15.38 ([Fig. 1A]), in the setting of borderline hepatomegaly. However, the corresponding CT images showed no discrete focal hepatic lesions ([Fig. 1B]). Additionally, subcentimetric hypermetabolic lymph nodes were seen in the highest mediastinal (SUV_max 8.43), right paratracheal (3.91), subcarinal (SUV_max 4.45), and bilateral hilar (SUV_max 3.61) regions. These nodes were considered insignificant due to their size and low FDG avidity. There was also decreased physiological activity of [¹⁸F]FDG observed in the myocardium and kidneys ([Fig. 2]). In view of the diffuse hepatic FDG uptake on PET/CT, a liver biopsy was performed. Histopathological analysis revealed features consistent with Sarcoidosis, favoring a granulomatous etiology over an infectious one ([Fig. 3A, B]).

Fig. 1 (A) [¹⁸F]-FDG PET/CT image showing diffusely increased FDG uptake in the liver (SUVmax 15.38). (B) Computed tomography image showing boderline hepatomegaly with no focal liver lesions.

Fig. 2 Maximum intensity projection (MIP) images of [¹⁸F]-FDG PET/CT showing diffusely increased liver uptake with decreased physiological uptake in myocardium and kidneys - HEPATIC SUPER SCAN.

Fig. 3 (A and B) Histopathological slides of liver biopsy showing granuloma formations (black arrows), consistent with sarcoidosis and indicative of a non-caseating granulomatous etiology.

After discussing with the Multidisciplinary Tumor Board, it was determined that there were no lymphatic or perilymphatic pulmonary nodules indicating lung involvement. Ultimately, a diagnosis of “hepatic sarcoidosis” was made, and the patient was prescribed oral steroids at a dosage of 30 mg, which was tapered over a 6-month period. During the follow-up, there was a significant improvement in the patient's clinical condition.

 

MissingLinkText

Discussion

Sarcoidosis, a multisystem disease, is characterized by the presence of noncaseating granulomas. The lungs are the most common site of disease involvement. However, hepatic involvement occurs in up to 70% of patients.

Most patients with liver involvement are asymptomatic, while some may present with nonspecific findings. It is important to differentiate hepatic sarcoidosis from other autoimmune and granulomatous liver diseases.[2] Our patient also presented with nonspecific symptoms with no positive findings in the general and systemic examination.

Laboratory investigations were inconclusive for a definitive etiology, except for an isolated elevation in serum alkaline phosphatase. While elevated alkaline phosphatase is the most frequently observed liver function abnormality in hepatic sarcoidosis, it is reported in only approximately 15% of patients with histologically confirmed disease.[3] Elevated levels of ACE have been observed, which is also a characteristic associated with sarcoidosis.[4]

Multimodality imaging plays a major role in the case of isolated hepatic sarcoidosis. [¹⁸F]-FDG PET/CT played a crucial role in guiding the biopsy site in this case, as conventional CT imaging did not demonstrate any focal hepatic lesions. Hepatomegaly, the most common liver abnormality detected on CT in hepatic sarcoidosis, was observed in our patient.[3] Other common CT findings in sarcoidosis with hepatic involvement include multiple small focal hepatic lesions, which typically have an average diameter of approximately 1.0 cm. These lesions are rare and occur in less than 5% of patients. The hepatic lesions are only visible during the venous phase, occurring 1 minute after the administration of the contrast medium. This contrasts with metastases, which are typically visible in both the baseline and contrast phases.[3] [4] The diagnosis of “hepatic sarcoidosis” was confirmed definitively on histopathology, in the form of predominantly portal-based granulomatous inflammation with focal necrosis. The hallmark of sarcoidosis is generally the formation of epithelioid granulomas that are typically noncaseating.[2]

The term “superscan” is usually used in skeletal scintigraphy. Similarly, superscan patterns have also been described in [¹⁸F]-FDG PET CT scanning. Usage of the term “superscan” implies sequestration of radiopharmaceutical in an organ or organ system with loss or reduction in the amount of activity detected in those organs normally associated with significant physiologic uptake of [¹⁸F]-FDG, such as the kidneys, brain, or myocardium.[4] Hepatic superscan ([Fig. 2]) is characterized by intense uptake in the liver with suppression of the background physiological activity.[5] Superscan appearance in the liver in [¹⁸F]-FDG PET is usually associated with malignancy, like massive liver metastases (commonly from a breast primary), primary hepatic lymphoma, diffuse angiosarcoma of the liver, secondary lymphomatous or leukemic involvement of the liver, and infective etiology like TB.[5] Rarely, even infiltrative disorders like sarcoidosis can cause a superscan appearance as noted in our patient.

Steroids have been the mainstay of treatment for systemic and pulmonary sarcoidosis.[6] Case reports describe beneficial effects of Prednisone and the augmentation of cytotoxic and anti-tumor necrosis factor-α therapy.[7] In our study, the patient had significant clinical improvement on steroids.

This case underscores the vital role played by functional imaging modalities such as [¹⁸F]-FDG PET in the early diagnosis and timely management of patients presenting with obscure symptoms.

 

MissingLinkText

Learning Points

• Sarcoidosis is a multisystem disease, and the association between pulmonary and hepatic sarcoidosis is reported in only 13% of cases, and isolated extrapulmonary involvement is rare.

• In case of diagnostic dilemmas, [¹⁸F]-FDG PET/CT plays a major role.

• In cases of diffuse hepatic uptake of [¹⁸F]-FDG, liver biopsy, when performed under ultrasound guidance, gives a good yield for diagnosis.

• Hepatic superscan or hot liver should not be misinterpreted as hepatic metastasis alone, as a similar appearance may be noted in infective and infiltrative conditions.

 

MissingLinkText

 

MissingLinkText

Conflict of Interest

None declared.

• References

• 1 James WE, Koutroumpakis E, Saha B. et al. Clinical features of extrapulmonary sarcoidosis without lung involvement. Chest 2018; 154 (02) 349-356
• 2 Tadros M, Forouhar F, Wu GY. Hepatic sarcoidosis. J Clin Transl Hepatol 2013; 1 (02) 87-93
• 3 Ufuk F, Herek D. CT of hepatic sarcoidosis: small nodular lesions simulating metastatic disease. Pol J Radiol 2015; 80: 945-954
• 4 Farina R, Clemenza M, Borzì SR, Basile A. Hepatic sarcoidosis: lesson based on a case report. J Med Ultrasound 2022; 31 (04) 318-322
• 5 Manov JJ, Roth PJ, Kuker R. Clinical pearls: etiologies of superscan appearance on fluorine-18-fludeoxyglucose positron emission tomography-computed tomography. Indian J Nucl Med 2017; 32 (04) 259-265
• 6 B V, C R, v M B, Muralee M, Raj J. Hot liver on 18F-FDG PET/CT imaging-a quandary for oncoradiologists in South Asia. BJR Case Rep 2020; 6 (02) 20190097
• 7 Shah N, Mitra A. Gastrointestinal and hepatic sarcoidosis: a review article. Clin Liver Dis (Hoboken) 2021; 17 (04) 301-307

Publication History

Article published online:
15 July 2025