Teaching Case

A 62-year-old female presented to the GP with several weeks of fever, diarrhoea, vague right-upper-quadrant pain and raised inflammatory markers (CRP, WCC). Given the fairly non-specific symptoms, a CT was performed demonstrating a liver and osseous lesion that were deemed suspicious. This resulted in referral to a quaternary cancer centre.

CT showed a hypoenhancing 28mm segment 8 liver lesion with an ill-defined perilesional hyperenhancement on arterial phase. It was heterogeneously hypoenhancing on portal-venous phase and demonstrated mild hyperenhancement with central washout on delayed phase. L4 vertebral body contained a well-defined lytic lesion (Figure 1).  

Multidisciplinary meeting 2 weeks post CT deemed imaging findings indeterminate, prompting further MRI and laboratory work-up. Liver function tests and tumour markers were normal. MRI liver with hepato-specific contrast (Gd-EOB-DTPA) was performed 3 weeks after CT. The lesion was T1-hypointense with a T2-hyperintense rim, showed no diffusion-restriction, similar contrast enhancement pattern to CT, and no hepatobiliary contrast uptake (Figure 2). L4 lesion had typical benign features (Figure 3).

Additionally, subtle caecal wall thickening was noted on CT and MRI (not reported on prior CT) (Figure 4). Subsequent colonoscopy biopsy confirmed amoebic colitis (Figure 5) resulting in the liver lesion diagnosed as atypical amoebic liver abscess (ALA).

Amoebiasis is a faecal-orally transmitted parasitic E. Histolytica infection that commonly affects travellers from (sub)tropical regions and people subject to poor sanitation, malnutrition, and immunosuppression [1-3]. Developed East-Asian countries have also seen an emergence in coinfection with HIV-1 due to oral-anal sexual contact [4].

E. Histolytica infection most commonly causes amoebic colitis, which usually occurs within three weeks of exposure. Diagnosis is made by stool microscopy, antigen testing, or PCR [2]. Radiological findings show typical inflammatory colonic wall changes (e.g., thickening, ulcerative lesions) and most affected sites are the caecum and rectum with sparing of the ileum [5].

ALA is the most common extraintestinal manifestation of amoebiasis.  Usual symptoms are as described in our case; however, they commonly evolve within 20-weeks post-exposure [6]. On US, ALA may be seen as a rounded, well-defined hypoechoic mass. It can show thin peripheral calcification on US and CT. ALA CT findings demonstrate features similar to a bacterial liver abscess with a predominant hypoenhancing mass demonstrating mild extralesional rim enhancement, however, a mild peripheral intralesional hyperenhancement on delayed phase is less common in bacterial abscess. MRI shows similar enhancement pattern to CT with additional information of no restricted diffusion, and no Gd-EOB-DTPA contrast uptake on hepatobiliary phase [7].

In our case, ALA was not considered as differential diagnosis since symptoms were of extreme late onset 4-years post travel to India, and travel history not obtained until after final diagnosis was made. Initial CT report deemed the liver and L4 vertebral body lesion as suspicious. Multidisciplinary management including radiology sub-specialist reporting at our cancer centre lead to the diagnosis of amoebic colitis with ALA. The patient underwent successful antimicrobial therapy (metronidazole, paromomycin) with resolution of colonic findings [8]. Follow-up 6-week post-treatment US was unable to visualise the high subcapsular ALA. Therefore, serial MRIs were performed that showed minimal residual scarring at 18 and 24 months (Figure 6) after which the patient was discharged from further surveillance.

Any newly detected liver lesion requires careful evaluation of prior medical, clinical and travel history as well as laboratory and imaging findings to guide further management [9]. Complex cases should be reported by a sub-specialised radiologist and undergo multidisciplinary discussion to ensure optimal outcomes [10]. Liver tissue sampling may be required during diagnostic workup [11], however, a percutaneous biopsy of uncomplicated ALA (lesion <10cm) should be avoided due to higher risk of liver rupture, seeding, and peritonitis [12].