SANT is a solitary entity distinguishing from other splenic vascular tumors and firstly defined by Martel et al because of its unique pathology [1]. The incidence of SANT remains unknown due to its rarity. In previous literatures, SANT mainly occurs in middle-aged population with a slightly female inclination and the mean age at onset was 50 years, which is also supported in our case [5]. However, occurrence of SANT shows a young age trends in recent report [6, 7]. Youngest SANT patient was a 7-month-old infant with splenomegaly [8]. Most cases are found incidentally since most patients are asymptomatic. Majority symptomatic patients attended to clinic with main complaints of abdominal discomfort, others were nonspecific such as flank pain, weight loss, fatigue, night sweat, and mild fever (9).
With increasing cases reported, radiologist and physicians tried to conclude imaging characters of SANT in order to get preoperative diagnoses. On non-enhanced plain CT scan, SANT presented as hypodense mass predominantly, some as equal-density, and partial cases have small central calcification [10]. Further enhanced CT presented solitary well- circumscribed hypodensity lesion comparing to background spleen in artery phased. The contrast between lesion with parenchyma of the spleen was significant in rapid enhanced phased and diminished progressively in portal-venous phased and delayed phased [11]. Karaosmanoglu et al firstly report imaging on MRI, which presented as central hyperintense area simulating hemorrhage on T1-weighted MRI. What’s more, they described the enhancement of SANT as progressively centripetal infiltration and the specific pattern was vividly named as “spoke-and-wheel” [12]. In Jianbing Ma’s literature, “spoke-and-wheel” pattern in CT or MRI examination can be the key for SANT diagnoses with 58% occurrence rate in total 12 patients [13]. However, only 4 of 12 cases were diagnosed as SANT preoperatively indeed probably due to its rarity. Profound research on correlation between pathological and radiological characters demonstrated that spoke-and-wheel imaging is referenced to a stellate collagen stroma core surrounded by angiomatoid nodules that are separated with proliferative fibrous septa [10]. As is shown in Table1, there is few preoperative diagnoses cases reported and we were the one of several cases. In presented case, SANT was nearly iso-density in both non-enhanced CT and pre-contrast T1、T2 weighted on MRI, and T2 weighted could observed satellite hypodensity septa in center. The multiple phase imaging of CT was consistent with previous report, which was enhanced progressively but remain hypodensity to background. Although spoke-and-wheel was not presented, central satellite hypodensity septa existed lasting the whole enhancement of T1 weighted on MRI. By summarized previous literature, we repute that there are two typical types of enhanced imaging characters on CT and MRI:1) enhancement started from peripheral part in progressively way presenting as spoke-and-wheel pattern; 2) enhancement evaluated progressively in entity way with or without hypo-intensity septa in center. Our case belongs to the later one. Similar to spoke-and wheel pattern, we suppose that satellite hypo-intensity septa are also corresponded to the colloid scar in center of gross. Another features we learned is that the CT value of SANT remain lower to the background of spleen during multiple phase. We believe that these features are helpful in preoperative diagnosis when spoke-and-wheel sign was absent.
Gray-scale ultrasonography usually shows a heterogeneously hypoechoic or isoechoic mass with hypoechoic rim compared to the surrounding splenic parenchyma. The lesion appeared “spoke-and-wheel” enhancement pattern as well on contrast sonography [14, 15]. Our case presented as heterogeneously majority isoechoic mass with hypoechoic radio-like linear area in center, which is similar to T2-weighted on MRI (Fig. 3 and Fig. 2A).
Positronemission tomographyCT(PET-CT) is a powerful examination mainly applying in malignant tumor follow-up. SANT presented slight FDG accumulation, similar to tumor metastasis. John et. concluded that SANT can be a differential diagnosis in the patient with malignant tumor history [16, 17].
Needle biopsy possesses excellent accuracy in preoperative diagnose despite accompanying with the risks of bleeding and needle path metastasis. Literature shows that bleeding risk of spleen needle biopsy can be retained in very low level under the ultrasonic guidance [16, 18].
Laparoscopic splenectomy is a prevalent therapy approach for variety spleen benign lesions, in which SANT accounted for 1.7%[4]. In our case, laparoscopic splenectomy was implemented in consideration that SANT is a benign mass and laparoscopic surgery has been surgery mature as well as regular in our department. In a series study with 37 cases, laparoscopic partial splenectomy demonstrated a great advantage in the sequent complication of surgery compare to total splenectomy [19].
Pathology is gold standard for SANT diagnosis. The gross appearance of resected spleen is coincided with spoke-wheel pattern in CT and MRI imaging, which presented as a wellcircumscribed mass with a stellate white stroma at the center [10]. Under microscope, classic pathological characters are as follow:i) multiple angiomatoid nodules are overspread in the horizon separated by dense collagen fibrosis and fibroid rims. ii)Individual nodule is composed of slit-shaped, round, or irregularly shaped lumens lined by swollen endothelial cells. iii)numerous red blood cells with scattered inflammatory cells are crowded in the inflammatory cells. iv)Three typical types blood vessels are presented with immunohistochemical staining cord capillary-like type with CD34、CD31 co-expression and absence of CD8-, sinusoids-like type (CD34-/CD8+/CD31+), and small veins-like type (CD34-/CD8-/CD31+) [1, 20]. Those features mentioned above can be found in our case. Additionally, some researchers detected plenty IgG4-positive plasma cells that and proposed SANT as an IgG4 related disease [21, 22]. But the hypothesis was not approved by advanced studies, in which cheng et al revealed that SANT is a reactive lesion originated polyclonally rather than a neoplasm [23]. What’s more, no cases associated with IgG4 disease has been reported up to date.
In summary, SANT is potential to be diagnosed preoperatively when imaging features are profoundly comprehended. Laparoscopic splenectomy is a reliable and effective therapy option for SANT treatment or diagnosis.