sclerosing angiomatoid nodular transformation of the spleen
Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a recently recognized, rare, non-neoplastic vascular splenic lesion of uncertain etiology.
Terminology
The term SANT first appeared in the literature in a 2004 paper by Martel et al. which examined a series of 25 cases . This relatively uncommon splenic lesion had however been recognized earlier by other authors under different names such as splenic hamartoma, cord capillary hemangioma, and multinodular hemangioma .
Epidemiology
According to older studies, it is most commonly encountered in middle-aged adults, with a mean age of presentation ~50 years with a female-to-male ratio of 2:1 .
A more recent review (n= 97), however, showed that 44.3% of the reported cases were male. As more cases are reported it is expected that this apparent gender bias will disappear .
Clinical presentation
The majority of cases are incidentalomas. When presenting with symptoms, abdominal pain predominates . Clinically, it may manifest with splenomegaly and pancytopenia.
Pathology
On microscopy, it is typically a well-circumscribed mass of red-brown nodules, alternating with band-like stromal tissue, often forming a central fibrous stellate scar.
Histology shows numerous nodular erythrocytes, stromal components collagenous bands containing myofibroblasts, hemosiderin-laden macrophages, lymphocytes and plasma cells.
Immunohistochemically, there are three distinct types:
Radiographic features
Ultrasound
Usually characterized as a well-circumscribed hypoechogenic mass .
CT
Common presenting as a solitary and well-circumscribed splenic mass with smooth or lobular borders, variable in size.
- NECT: homogeneous, iso- to mild hypodensity compared to surrounding spleen
- post-contrast phases: comparatively hypovascular center with an enhancing rim and radiating vascularized tissue penetrating from the periphery toward the center of the lesion . Progressive central enhancement with delayed imaging thought to be the result of contrast penetrating the center of the lesion from the vascular rim - "spoke wheel" pattern
MRI
- T1: most commonly heterogeneous but low to an intermediate signal intensity
- T2: typically low signal (in contrast to most of the differential diagnoses stated below)
- T1 C+ (Gd): usually peripheral and septal enhancement in above mentioned “spoke wheel” pattern with a central hypoenhancing stellate scar
Nuclear medicine
FDG-PET
Few cases, slightly hypermetabolic with increased SUV measurements - compared to hepatic and surrounding normal splenic uptake. Abundance of cells, including hemosiderin-laden macrophages, myofibroblasts, lymphocytes, and plasma cells as aforementioned, may account for splenic SANT’s FDG avidity . However, other authors have reported SANT cases without FDG-PET activity .
SPECT-CT
Scintigraphically cold, however, this fairly non-specific sign will not aid in diagnosis. The absence of reticuloendothelial cells within the SANT lesion may account for this lack of uptake of Tc-sulfur colloid .
Treatment and prognosis
The lesion is benign without risk of malignant transformation. Treatment with splenectomy allows for histopathological characterization, which is the gold standard .
Although core biopsy is a sensitive and specific way to diagnose both hematologic and non-hematologic splenic lesions, the risk of intraperitoneal seeding (if the lesion is biopsied and proves to be malignant e.g. angiosarcoma) should be kept in mind .
Differential diagnosis
For a differential of benign, indeterminate, and malignant splenic lesions. See the list of splenic lesions and anomalies.
Most of these demonstrate different signal intensities and/or more numerous lesions, potentially enabling differentiation from SANT.
Siehe auch:
Assoziationen und Differentialdiagnosen zu sklerosierende angiomatöse noduläre Transformation der Milz:
