Multidetector CT and MRI findings in periportal space pathologies

2.1. Pathologies of portal vein 

Portal vein is the most prominent anatomic structure in the periportal space and portal vein pathologies are the most common cause of periportal pathologies. Periportal cavernomatous transformation is a consequence of chronic portal vein thrombosis [1]. CT and MR findings show absence of portal vein and presence of small tortuous collateral venous structures at the periportal region (Fig. 2). Most of the time cavernomatous transformation involves both intra- and extrahepatic periportal regions. Sometimes segmental cavernomatous transformation can be seen as a result of isolated right or left portal vein thrombosis. Portal vein thrombosis can develop due to invasion of tumors and inflammation, which can involve segmental branches or rarely all-portal venous structures (Fig. 3) [1], [2]. Hepatocellular carcinoma has a propensity to invade portal vein and can sometimes invade adjacent biliary system simultaneously (Fig. 4) [3].

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Fig. 2. (A and B) Forty-seven-year-old woman with periportal cavernomatous transformation due to chronic portal vein thrombosis. Axial CT images show absence of portal vein and collateral venous structures are seen in the periportal region. Biliary dilatation is seen which can be caused by compression of collateral veins. Note venous collaterals in gallbladder wall. (C and D) Forty-seven-year-old woman with intrahepatic periportal cavernomatous transformation due to intrahepatic portal vein thrombosis. Coronal MIP and axial CT images show patency of main portal vein and collateral veins in right (arrow) periportal space. Collaterals were absent in left periportal space.

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Fig. 3. Fifty-year-old man presented with jaundice and weight loss with a history of chronic hepatitis B virus infection. Axial CT images show diffuse thrombosis of portal vein and its branches. Biopsy revealed findings consistent with undifferentiated hepatocellular carcinoma.

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Fig. 4. Eighty-two-year-old woman with jaundice and weight loss. (A) Axial CT image shows tumoral infiltration of right portal vein (short arrow) and right hepatic biliary duct (long arrow) and biliary dilatation in left lobe. (B) Oblique coronal CT image shows extension of tumor into right portal vein (arrow) to better extent. (C and D) Arterial phase oblique coronal MIP images show infiltration of hypervascular tumor (asterisk) into choleduct (long arrow). Note hepatic artery (short arrow) in between portal vein and choleduct.

2.2. Pathologies of hepatic artery 

Most common hepatic artery pathologies are thrombosis and hepatic artery aneurysms. Hepatic arterial thrombosis is rare and can develop in patients who undergo liver transplantation and transarterial chemoembolization [4], [5]. Arterial aneurysms of intrahepatic branches of hepatic artery can be seen in patients with polyarteritis nodosa, vasculitis and sepsis (Fig. 5) [6], [7].

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Fig. 5. Eight-year-old boy with periarteritis nodosa with multiple hepatic artery aneurysms. (A and B) Multidetector CT angiography, coronal and axial MIP images show aneurysms of right and left hepatic arteries (arrows). Note faint opacification of portal venous system.

2.3. Pathologies of periportal lymphatics 

Lymphatics are also found in the periportal region which are not visible in normal patients. Lymphatics and lymph nodes can be involved by a variety of diffuse infiltrative processes. Lymphatic dissemination of primary liver tumors (hepatocellular and cholangiocellular carcinoma) or periportal involvement of lymphoma or langerhans histiocytosis can cause expansion of periportal area in the form of diffuse soft tissue density (Fig. 6) [8], [9]. In patients with lymphoma and langerhans histiocytosis lymph node enlargement can be visible by radiologic imaging.

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Fig. 6. Forty-year-old woman with lymphoma. (A and B) Axial CT images show diffuse involvement of periportal space by lymphoma extending to right (arrow) and left (arrowhead) periportal space. Note multiple parenchymal liver metastases. (C and D) Four-year-old boy with periportal lymphoma. Axial CT images show periportal involvement and rapid resolution at 1-month follow-up.

2.4. Pathologies of periportal nerves 

Periportal nerves are normally not visible by radiologic imaging. Pathologic involvement of neural structures in the periportal region is rare and can be seen in patients with plexiform neurofibromatosis [10]. Periportal involvement can be diffuse or lobar in distribution and appears hypodense on CT and hyperintense on T2-weighted MR images similar to neurofibromatosis elsewhere in the body (Fig. 7). Extension of periportal involvement to mesenteric root can be seen and may allow differentiation from other infiltrative pathologies.

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Fig. 7. Four-year-old boy with neurofibromatosis type I. (A) Axial CT image shows hypodense appearance around main and right portal vein consistent with plexiform neurofibromatosis. (B and C) Axial T2-weighted MR images show hyperintense periportal pathology consistent with neurofibromatosis. Note absence of involvement around left portal vein (arrow) indicating lobar intrahepatic involvement. (D and E) Coronal T2-weighted MR images show main and right periportal involvement extending to mesenteric root (arrow). (F and G) Three-year-old boy with neurofibromatosis. Axial MR images show diffuse involvement around main, right (short arrow) and left (long arrow) portal veins.

2.5. Pathologies of biliary system 

Biliary system can be dilated in Caroli's disease diffusely with characteristic radiologic findings (Fig. 8) [11], [12]. Dot sign on gadolinium-enhanced MRI appears as a tiny dot or an internal septum showing strong contrast enhancement which represents a portal radicle surrounded by a dilated bile duct [12]. Also, similar but less prominent dilatation can be seen in patients with congenital hepatic fibrosis, Rendu–Osler–Weber disease, primary sclerosing cholangitis [13], [14]. Segmental biliary dilatation can be caused by sclerosing cholangitis, tumors (cholangiocarcinoma and metastases) and iatrogenic causes [15].

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Fig. 8. Two patients with Caroli's disease. (A) Axial postcontrast T1-weighted MR image shows dilatation of biliary system around portal vein branches. (B) Axial CT image shows same findings.

2.6. Pathologies of periportal space (periportal halo) 

Periportal space is a potential space encircling above mentioned periportal structures. This space can be expanded by inflammation, tumor infiltration, bile duct proliferation, hemorrhage and edema causing hypodense appearance on CT and hyperintense appearance on T2-weighted MR images which is known as periportal halo or tracking (Fig. 9). Periportal halo can mimic biliary dilatation. Presence of hypodense appearance on both sides of main portal vein can allow differentiation from biliary dilatation. A variety of diseases and conditions can cause periportal halo [16], [17]. Periportal halos due to blood or elevated venous pressure are commonly seen in patients with blunt liver trauma. Periportal edema may cause this sign in patients with congestive heart failure and secondary liver congesion, hepatitis, or enlarged lymph nodes and tumors in the porta hepatis which obstruct lymphatic drainage. This sign can also be seen in liver transplants and in recipients of bone marrow transplants.

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Fig. 9. Periportal halo. (A) Forty-one-year-old man admitted after motor vehicle accident. Axial CT image shows diffuse linear hypodensity around portal vein branches consistent with periportal edema or hemorrhage due to blunt liver trauma. (B) Forty-three-year-old woman with autoimmune hepatitis. Fat saturated axial T2-weighted MR image shows diffuse hyperintense signal around portal vein consistent with periportal inflammation. (C) Sixty-six-year-old man who underwent gastrectomy. Axial CT image shows hypodense appearance around left portal vein (short arrow) consistent with lobar distribution of periportal halo. Note absence of a similar appearance around right portal vein (long arrow).

Also, recently CT and MR findings of diffuse periportal fatty infiltration have been described as a distinct pathology [18]. This pathology has been reported in alcoholic patients and can be seen alone or in combination with fatty infiltration around hepatic veins. Periportal fat infiltration can also be segmental (Fig. 10) [19]. Sometimes periportal fat tissue can be seen around left portal vein as a normal finding (Fig. 11).

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Fig. 10. Segmental periportal fatty infiltration. (A and B) Axial CT images show hypodense appearance around umbilical segment of left portal vein (arrow) and segment 3 branch (arrow) in periportal space. Biopsy confirmed presence of fatty infiltration and excluded a lesion.

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Fig. 11. Axial CT image shows normal fat tissue around umbilical segment of left portal vein which is a frequently seen normal appearance. Presence of fat probably indicates extrahepatic course of left portal vein.