Abstract
Foci of splenic tissue separated from the spleen can occur as a congenital anomaly. Isolated nodules of splenic tissue are called accessory spleens or spleniculli. However, nodules of splenic tissue can merge with other organs during embryonic development, in which case we speak of spleno-visceral fusions: most often, they merge with the tail of the pancreas (thus forming spleno-pancreatic fusion or an intrapancreatic accessory spleen), with the reproductive gland (i.e., spleno-gonadal fusion), or with the kidney (i.e., spleno-renal fusion). Our case report describes the fusion of heterotopic splenic tissue with the right adrenal gland, which was misinterpreted as a metastasis of a renal cell carcinoma. To the best of our knowledge, this is the first reported case of spleno-adrenal fusion. Spleno-visceral fusions usually represent asymptomatic conditions; their main clinical significance lies in the confusion they cause and its misinterpretation as tumors of other organs. We believe that the cause of retroperitoneal spleno-visceral fusions is the anomalous migration of splenic cells along the dorsal mesentery to the urogenital ridge, together with primitive germ cells, at the end of the fifth week and during the sixth week of embryonic age. This theory explains the possible origin of spleno-visceral fusions, their different frequency of occurrence, and the predominance of findings on the left side.
Highlights
Congenital heterotopia of splenic tissue can occur in the form of isolated accessory spleens, which are relatively common, or in the form of spleno-visceral fusions, i.e., the association of splenic tissue with another abdominal organ
In similar conditions that are more common in clinical practice, such as splenosis or accessory spleens mimicking a neoplastic lesion, the suspicion may be confirmed by 99m Technetium heat-damaged red blood cell scintigraphy combined with single-photon emission computed tomography (CT)
There is a theory according to which continuous spleno-gonadal fusion, with its associated high incidence of limb and jaw defects, is probably caused by a teratogenic insult between the fifth and eighth weeks of embryonic age, whereas discontinuous spleno-gonadal fusion represents a rare variant of an accessory spleen [29]
Summary
Congenital heterotopia of splenic tissue can occur in the form of isolated accessory spleens, which are relatively common, or in the form of spleno-visceral fusions, i.e., the association of splenic tissue with another abdominal organ. These are asymptomatic conditions; their main clinical significance lies in the confusion they cause and its misinterpretation as tumors of other organs. Cases or even smaller groups of patients with splenopancreatic, spleno-gonadal, and spleno-renal fusion have been published. Our article presents a case report of fusion of heterotopic splenic tissue and the right adrenal gland. We present a possible embryological basis for this anomaly, and for other spleno-visceral fusions in the retroperitoneum
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