Elliot K. Fishman M.D.
Johns Hopkins Hospital

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“The initial “white paper” from the American College of Radiology (ACR) incidental findings committee recommends further evaluation and/or follow-up imaging for all incidental splenic masses greater than 1 cm that do not have clearly benign features at imaging at the time of detection. The majority of such solid splenic nodules and masses are benign, with hemangioma being the most frequent diagnosis. However, CT imaging characteristics of benign and malignant splenic masses often overlap, making definitive differentiation difficult.”
The Incidental Splenic Mass at CT: Does It Need Further Work-up? An Observational Study 
Siewert B et al.
Radiology 2018; 287:156–166

Purpose: To evaluate whether an incidentally noted splenic mass at abdominal computed tomography (CT) requires further imaging work-up. 
Conclusion: In an incidental splenic mass, the likelihood of malignancy is very low (1.0%). Therefore, follow-up of incidental splenic masses may not be indicated. 
The Incidental Splenic Mass at CT: Does It Need Further Work-up? An Observational Study 
Siewert B et al.
Radiology 2018; 287:156–166

“Such incidental findings include masses in the spleen, which have been reported as incidental findings in greater than 14% of autopsies, and most commonly represent hemangiomas, cysts, hamartomas, lymphangiomas, or granulomas.”
The Incidental Splenic Mass at CT: Does It Need Further Work-up? An Observational Study 
Siewert B et al.
Radiology 2018; 287:156–166

“Follow-up of splenic masses incidentally detected at CT (i.e., in patients with no evidence of previous or newly diagnosed malignancy and no systemic symptoms or localized pain) does not appear to be indicated.”
The Incidental Splenic Mass at CT: Does It Need Further Work-up? An Observational Study 
Siewert B et al.
Radiology 2018; 287:156–166

Accessory spleens are common

• failure of fusion, usually near hilum
• usually < 3 cm, round, enhance like spleen
• don’t mistake accessory spleens for nodes

Lobulations are very common

• clefts cause lobulations
• don’t mistake clefts for lacerations or infarcts

Variable circulatory routes through the spleen

• white pulp (lymphatic follicles and RE cells)
• red pulp ( interspersed vascular lakes)

Routine scanning

• Single phase acquisition
• 60-70 second delay

Suspected splenic artery aneurysm or bleed

• Dual phase acquisition
• 25 and 60-70 second delay

Patterns of Enhancement

• serpentine, cord-like enhancement most common
  • more pronounced with fast injection rates
  • exaggerated in certain patients
    • decreased cardiac output or heart failure
    • splenic vein occlusion
    • portal hypertension
  • becomes uniform on delayed scans

Accessory spleen

• Found in 10-20% of individuals.
• Within the tail of the pancreas is the second common site of the accessory spleen, and can mimic hypervascular pancreatic tumor (e.g. neuroendocrine tumor)
• Accessory spleen can be a site of relapse of hypersplenism after splenectomy in patients with a hematologic disorder with hypersplenism.

Splenosis

• Ectopic splenic tissue caused by autotransplantation of splenic cells resulting from traumatic disruption of the splenic capsule via trauma or surgery.
• More numerous and widespread than accessory spleens.

Wandering spleen

• The spleen migrate from its normal position due to congenital or acquired laxity of the splenic suspensory ligament.
• At risk of vascular pedicle torsion and splenic infarct.

Polysplenia

• A rare complex syndrome, consists of situs ambiguous with features of left isomerism (bilateral left-sidedness)
• Multiple spleen in right or left upper quadrant, single, lobulated spleen, or a normal spleen
• Anomalous position of abdominal viscera, short pancreas, abnormal bowel rotation, cardiovascular anomalies

Asplenia

• Absent spleen, situs ambiguous, multiple anomalies including cardiovascular anomalies (typically more complex than those with polysplenia), bowel malrotation, genitourinary tract anomalies.

“Splenosis is an acquired form of ectopic splenic tissue that typically arises after trauma or splenectomy. It is often an incidental image finding in an otherwise asymptomatic patient, but the spectrum of symptoms varies based on the site of implantation. Radiologists should be familiar with the imaging features of splenosis to avoid mistaking it for malignancy. Splenosis has identical imaging features to that of the native spleen on US, CT, MRI, and nuclear medicine examinations. Therefore, when the radiologic findings support the diagnosis of splenosis, the patient can be spared invasive procedures for tissue sampling.” 
Abdominal and pelvic splenosis: atypical findings, pitfalls, and mimics 
Travis Smoot et al.
Abdom Radiol (NY) 2022 Mar;47(3):923-947

“Ectopic splenic tissue can be found in the body in three forms: Splenosis, accessory spleen, or wandering spleen. Splenosis is the acquired form of ectopic splenic tissue that arises after traumatic splenic rupture or splenectomy. When the capsule of the spleen is disrupted, splenic autoimplantation can occur throughout the body by direct seeding or hematogenous spread. Splenosis is often an incidental finding, as most patients are asymptomatic, so the true incidence is unknown. However, studies suggest that up to 67% of patients with a compromised splenic capsule develop splenosis.”
Abdominal and pelvic splenosis: atypical findings, pitfalls, and mimics 
Travis Smoot et al.
Abdom Radiol (NY) 2022 Mar;47(3):923-947

“ If the diagnosis of splenosis remains uncertain on CT or MRI, a Tc99m-labeled Sulfur colloid (Tc-99 m-SC) or heat-dam- aged RBC (Tc-99 m-HDRBC) scan may be helpful given their high sensitivity and specificity for detection of ectopic splenic tissue. Using these radiologic methods, radiologists can distinguish splenosis from other lesions in a timely manner without excessive or undue invasive procedures.”
Abdominal and pelvic splenosis: atypical findings, pitfalls, and mimics 
Travis Smoot et al.
Abdom Radiol (NY) 2022 Mar;47(3):923-947

An accessory spleen, also called a supernumerary spleen, a splenule, or a splenunculus, is a benign and asymptomatic condition in which splenic tissue is found outside the normal spleen. Accessory spleens are a relatively common phenomenon with an estimated 10% to 30% of the population having one.