SNN of the liver is a rare benign lesion; to date fewer than 60 cases have been reported in the literature. Koea et al. reported one case taken from 500 referrals with liver masses presenting over a 2-year period [2
], Berry [3
] reported 2 lesions in 1,000 post mortems and Tsui et al. [4
] documented 7 lesions in 4,000 patients. Most of the reported cases have been in males and the majority have been seen in the seventh and eighth decades of life. However, a number of cases have been found in patients in their thirties and forties [5
], whereas Tsui et al. reported a case of a patient as young as 27 years old [4
]. SNN, despite its name, may also be multiple [8
Over three-quarters of these rare benign lesions occurred in the right lobe of the liver. In the initial description by Shepherd and Lee [1
], all SNNs were reported on the surface of the liver and most of them were located on the right side, probably because the right lobe of the liver is easy to examine, but also because of the possibility that trauma may be involved in the pathogenesis of these lesions. Only four of the reported SNNs were found in the left lobe [1
]. In a review of 21 cases performed by Imura et al., it was noted that in fifteen cases the tumor was ≤2.0 cm in diameter and that all the lesions were <5.0 cm; only in one case did the authors find a mass 8.5 cm in diameter [9
]. In the literature, there is a reported association with tumor pathology in >50% of cases [10
This kind of lesion is normally accidentally diagnosed during a workup for other pathologies or is an occasional finding during abdominal surgery or autopsy. In the majority of cases, this condition is clinically silent, and often the patients complain of nonspecific and unclear symptoms. SNNs are usually first detected at US examination. Some features, such as lobular shape, well-delineated margin, and close proximity to the hepatic inflow structures, are suggestive of SNN, but are nondiagnostic [2
]. Since conventional color/power Doppler imaging is insensitive to the slow flow of deep-seated blood vessels, the lack of blood flow signal cannot confirm a total absence of blood perfusion within the lesion. SNN usually appears as a well-defined lesion with no enhancement on contrast CT or MRI [11
] or US [12
], while some SNNs may have subtle peripheral enhancement on contrast MRI [13
Often the radiological findings of SNN of the liver are similar to those of hepatic metastasis or other liver masses, such as pseudotumor, lymphoma, regenerative and dysplastic nodules, or some infectious processes [14
]. Due to these similar radiological findings, making a correct differential diagnosis is often very difficult or impossible [13
]. The intraoperative US findings of the lesion also simulate hepatic metastasis, even though lesion multiplicity had been elucidated [13
]. Furthermore, the cytological evaluation of specimens obtained by needle biopsy is not useful to correctly distinguish between these nodules and hepatic metastasis, because it often reveals only the presence of necrotic tissue. Due to these difficulties, performing a liver biopsy in order to clarify the diagnosis may be mandatory.
From a pathological point of view, SNN appears well-delineated by a dense fibrohyalinized fibrotic capsule with a principally necrotic core containing an eosinophil granular matter combined with calcifications, cholesterol, foam cells, and some inflammatory cells. Characteristically Ziehl-Neelsen, Gram and PAS stains do not reveal bacteria or fungi, and the pathogenesis of these cases remains uncertain. The histological findings of our case were in keeping with the above-mentioned features.
The etiology of these rare benign lesions is still uncertain; at least three different hypotheses have been suggested as to their origin. Some authors argue that these nodules have a traumatic etiology or that they are the result of previous parasitic infestation [1
]. Others suggest that because of the finding of a ‘feeding vessel’ and the absence of a cystic space or other signs of parasitic infestation, the lesions could be the result of the sclerotic evolution of small hemangiomas [2
]. Finally, the possibility that a SNN of the liver may develop by two or more different mechanisms cannot be denied [11
]. We agree with this last hypothesis that at least two different pathogenetic mechanisms could be involved. To support this claim, we would like to show the histological differences between the case we report in this work and a previously observed case of ours (unpublished). In the latter, large feeding vessels were evident at the periphery of the lesion (fig. ). Furthermore, the central core was more fibrous than necrotic and Shikata's orcein staining, evidencing several circular-running elastic fibers, suggested the presence of sclerotic vessels (fig. ) with lumina occluded or reduced to a thin fissure, evidenced only by performing anti-CD31, anti-CD34 and anti-factor VIII immunostaining to highlight the presence of the endothelial cells (fig. ). Finally, Gomori's silver staining did not show the collapse of the reticular network, but evidenced some reticular fibers around the vascular lumina (fig. ). Consequently, we think that careful observation and special staining could be useful to highlight morphological differences in SNN, which suggest the hypothesis of a different histogenetic origin.
Fig. 2 a Large feeding vessels at the periphery of the lesion. The central core was more fibrous than necrotic. HE staining, overall magnification 50×. b Circularly running elastic fibers suggesting the presence of sclerotic vessels. Shikata's orcein (more ...)
To our knowledge, the natural history of SNN is still unclear. De Luca et al. in their report observed a reduction in size of SNN during follow-up [10
], whereas Imura et al. reported a case with rapid enlargement in diameter from 3 cm to >8 cm in the space of seven months [9
In conclusion, although the benign behavior of this lesion and the absence of symptomatology suggest that surgical resection is unnecessary, the radiological suspicion of SNN demands to perform a liver biopsy, and in case of failure, given the high association of SNN with malignant lesions, confirms resection as the treatment of choice in the management of this disease.