Imaging Features of Hepatic Small Vessel Neoplasm: Case Series

Potential conflict of interest: Nothing to report. Hepatic small vessel neoplasm (HSVN) is an entity described by Gill et al. in 2016 in a series of 17 cases collected over 5 years,(1) and has been recognized as a rare, benign, or low‐grade malignancy vascular neoplasm of the liver in the 2019 World Health Organization classification of tumors of the digestive system. No complete radiological description has ever been published. Our purpose was to describe the radiologic features of this entity. Case Series Four lesions were analyzed in 4 patients (3 male; mean age 70.8 ± 7.7 years; mean size lesion 21.3 ± 9.1 mm). All patients underwent contrast‐enhanced ultrasound (CEUS), CT, and MRI with extracellular contrast agent and histology. All lesions were nodular and well limited. In the arterial phase, the tumors always had a strong, early, continuous, thick but irregular rim enhancement (Figs. 1 and 2). On the two largest lesions (3.2 and 2.3 cm), we describe radial enhanced septa with a "flower petal shape." In the portal phase, lesions display a centripetal enhancement, leading in the delayed phase to a complete and homogenous enhancement (Fig. 1). Interestingly, in CEUS, in the delayed phase of the two largest lesions (3.2 and 2.3 cm), we found a persistent thick rim enhancement with a mild central washout (Fig. 1).FIG. 1: Case of an 80‐year‐old man having had ultrasound for renal insufficiency with hepatic nodule discovery. (A,C) Arterial phase CT (A) and CEUS (C) with a thick and nonuniform rim enhancement. (B) Delayed‐phase MRI with a centripetal enhancement and homogenization. (D) Delayed phase in CEUS with central mild wash‐out (arrow) and peripheral heterogeneity (arrow head).FIG. 2: Case 4 is a 63‐year‐old male with right upper pain. (A) T2 fat saturation showing a franc hypersignal. (B) Apparent diffusion coefficient showing no restriction. (C) T1 fat saturation without injection. (D) Second arterial phase after injection in multiphasic arterial displaying the rim enhancement and the "flower petal shape."In MRI, HSVN displayed a heterogeneous and homogeneous liquid hypersignal in T2‐weighted sequences with no apparent diffusion coefficient restriction (Fig. 2). Patients 2 and 4 both had a second smaller lesion with similar characteristics. For the first three cases, the radiologists suggested atypical hemangioma or rare vascular tumor; for the fourth they suggested the diagnosis of HSVN. Pathology is detailed in the Supporting Information. Discussion All HSVNs have the same enhancement pattern in arterial and portal phases in the three imaging modalities. The strong, early, continuous, irregularly thick rim arterial enhancement and the "flower petal shape" caused by early septa enhancement appear to be characteristic to HSVN. In pathology, HSVN is a vascular tumor of uncertain malignant potential that can mimic well‐differentiated angiosarcoma due to its ill‐defined borders and occasional moderate cytological atypia.(1) Distinguishing these two entities relies on morphological features and several immunochemical markers such as the proliferation index (Ki67) and p53.(1,2) Joseph et al. described frequent GNAQ and GNA14 mutations in HSNV, also found in various vascular malformations and benign neoplasm as congenital hemangiomas.(3) Gill et al. showed 1 patient with HSVN with a splenic mass and one case with an established activating hotspot mutation in PIK3CA, which is an oncogenic mutation in numerous cancers.(1) Thus, Gill et al. recommend complete resection and follow‐up of these patients. In imaging, hemangioma is the only serious differential diagnosis, as a result of its strong and homogeneous hyper‐T2 signal on MRI, and progressive centripetal enhancement. However the classic hemangioma has a peripheral globular discontinuous enhancement, whereas the HSNV has a thick continuous rim enhancement. This rim enhancement is early and can be missed if the arterial phase is not perfectly synchronized. This underlines the crucial interest of the multiphasic arterial MRI or CEUS. The differential diagnosis of angiosarcoma, which is the main differential diagnosis in pathology, is less problematic in imaging. Although the angiosarcoma may appear well circumscribed, its content and especially the classic marked T2 hyperintensity is usually heterogeneous. The "multiple nodules" type of angiosarcoma with small nodules remains a difficulty, however, because in the early stage the lesions may still be homogeneous. Lesions are usually small and solitary,(1) but a larger lesion (15.9 cm) was described.(4) In our series, 2 patients had a second hepatic lesion, suggesting that HSVN may be multiple in the liver. In conclusion, HSVN has a characteristic enhancement to suggest the diagnosis in imaging to guide the pathologist and must be recognized and differentiated from a hemangioma.