Management of Discrepant Imaging Findings: Accessory Spleen on Ultrasound vs. Unremarkable CT
No intervention is required for this imaging discrepancy, as accessory spleens are benign congenital variants that do not require treatment unless associated with specific hematologic conditions like idiopathic thrombocytopenic purpura. 1, 2
Understanding the Discrepancy
The apparent contradiction between imaging modalities is likely explained by the following:
Accessory spleens are present in approximately 16% of patients on contrast-enhanced CT and represent normal anatomic variants resulting from incomplete fusion of splenic tissue during embryologic development 2, 3
CT is superior to ultrasound for detecting accessory spleens, with characteristic features including well-marginated, round masses typically <2 cm that enhance homogeneously and identically to the normal spleen in all contrast phases 2, 3
The most common location (22% of cases) is posteromedial to the spleen, anterolateral to the upper pole of the left kidney, and lateral/posterior/superior to the pancreatic tail 3
When accessory spleens are <1 cm, they may appear lower in attenuation than the main spleen on CT due to partial volume effects, potentially explaining why it was not specifically mentioned in the prior CT report 3
Recommended Management Approach
Observation only is appropriate - no further imaging or intervention is needed 1, 2
Key Management Points:
Accessory spleens do not require treatment in asymptomatic patients and should be left alone 2
The only clinical scenario requiring intervention is when accessory splenic tissue is identified in patients with idiopathic thrombocytopenic purpura who have failed splenectomy, where imaging techniques can identify residual splenic tissue in up to 12% of splenectomized patients 1
Periodic monitoring is unnecessary unless the patient develops symptoms or has underlying hematologic conditions 2
When to Reconsider the Diagnosis
Re-evaluation with dedicated imaging should be considered if:
The patient develops left upper quadrant pain, which could indicate torsion of the accessory spleen (rare complication) 4, 5
The lesion grows on follow-up imaging, which would be atypical for an accessory spleen and warrant consideration of alternative diagnoses 2
Contrast-enhanced ultrasound (CEUS) or MRI can confirm the diagnosis by demonstrating enhancement patterns identical to the normal spleen in all phases, with MRI showing high signal intensity on diffusion-weighted imaging comparable to normal splenic tissue 4, 2
Common Pitfalls to Avoid
Do not pursue biopsy - accessory spleens cannot be reliably distinguished from retroperitoneal tumors by percutaneous biopsy, and biopsy is unnecessary for this benign finding 6
Avoid unnecessary surgery - being aware of this common anatomic variant prevents unnecessary surgical exploration 2, 6
Do not assume the CT "missed" pathology - the radiologist likely saw the accessory spleen but did not specifically comment on it as it represents a normal variant without clinical significance 3