Hepatic peliosis

Hepatic peliosis is a rare benign vascular condition characterised by dilatation of sinusoidal blood-filled spaces within the liver. There may be involvement of other organs, most commonly the spleen and bone marrow. It can be seen in a variety of settings and is important as appearances may mimic malignancy. 

Epidemiology

As the causes of peliosis are varied, the demographics will reflect the underlying cause.

Clinical presentation

Patients are usually asymptomatic ⁶ and thus the condition is discovered incidentally on imaging or autopsy. In some instances, lesions may be complicated by haemorrhage presenting acutely or result in hepatomegaly or liver impairment.

Pathology

The pathogenesis remains uncertain, with possible aetiologies including the breakdown of the sinusoidal borders, hepatic outflow obstruction and dilatation of the central vein of the hepatic lobule.

Histologically, hepatic peliosis is characterised by multiple mottled blood-filled cyst-like spaces within the liver with associated sinusoidal dilatation ^1,2. These vary in size from <1 mm to several centimetres in diameter.

Macroscopically, the liver appears dark or even purple, and usually, the entire liver is involved to a greater or lesser degree. Focal lesions may demonstrate central areas of haemorrhage.

Aetiology

• idiopathic: 20-50% 

• toxins

  • arsenic

  • polyvinyl chloride (PVC)

  • thorium oxide

• drugs

  • anabolic steroids

  • azathioprine

  • corticosteroids

  • diethylstilboestrol (DES)

  • immunoglobulin therapy

  • methotrexate

  • oral contraceptives

  • tamoxifen

  • 6-thioguanine (6-TG)

  • 6-mercaptopurine (6-MP)

• chronic illness

  • malignancy, particularly hepatocellular carcinoma

  • tuberculosis

  • leprosy

  • coeliac sprue

  • diabetes mellitus

  • necrotising vasculitis

  • haematologic disorders: Hodgkin disease, multiple myeloma

• infection in AIDS

  • bacillary peliosis caused by Bartonella henselae, Bartonella quintana and Rochalimaea henselae

• other 

  • renal or cardiac transplantation

Radiographic features

Unfortunately, appearances are non-specific with variable enhancement patterns. Typically, there are multiple lesions, ranging from a few large lesions to innumerable small lesions.

Ultrasound

Sonographic appearances are non-specific, usually demonstrating an irregular hypoechoic region/mass ².

CT

Appearance on pre-contrast CT is variable, depending on liver density, but is usually of multiple hypoattenuating lesions of variable size. Central haemorrhage may lead to areas of hyperattenuation and even dystrophic calcification ¹.

Following contrast administration, there is usually globular centrifugal (more common) or centripetal arterial enhancement with no washout, the lesion remaining slightly hyperattenuating compared to surrounding liver on portal venous phase ¹. Enhancement may be uniform or peripheral or irregular, but in contrast to cavernous haemangioma, it is usually continuous. There is no mass effect on neighbouring hepatic vessels ⁶.

MRI

Signal characteristics may be altered due to the presence of haemorrhage; however, in general:

• T1: typically hypointense (unless complicated by recent haemorrhage)

• T2: hyperintense

• T1 C+ (Gd): enhancement is typical, and is usually centrifugal (from centre outward)

Angiography (DSA)

• hypervascular with multiple vascular nodules

Treatment and prognosis

It is important not to drain peliosis, having mistaken it for a hepatic abscess, as haemorrhage can be life threatening ⁷.

Treatment depends on the cause. When a causative drug/toxin is suspected, withdrawal of that agent may result in resolution. If seen in the setting of HIV/AIDS, antibiotic treatment may be effective in eradicating B. henselae. If focal and haemorrhagic, resection may also be beneficial ¹.

Complications 

• hepatic failure

• portal hypertension

• rupture and haemorrhage

History and etymology

From the Greek word pelios, meaning "dusky" or "purple" ¹.

Differential diagnosis

General imaging differential considerations include:

• cavernous haemangioma

  • globular discontinuous contrast enhancement tends to be centripetal (periphery first) rather than centrifugal (centre first)

• hepatocellular carcinoma (HCC)

  • usually bright arterial enhancement with early washout

• hepatic abscess

  • fluid component does not enhance

• focal nodular hyperplasia (FNH)

  • when typical, are easy to distinguish: central scar; homogeneous arterial enhancement (except for scar); delayed enhancement of the scar; isoattenuating on portal venous phase; strong enhancement on hepatobiliary phase

• hepatic adenoma

  • may contain fat

• hypervascular metastases

• hepatic sinusoidal dilation: usually the enhancement pattern is different on CT/MRI ⁵