Accessory spleen-like masses in oncology patients: Are they always benign?

To assess retrospectively the significance of accessory spleen-like mass (ASLM) in oncology patients undergoing positron emission tomography/computed tomography (PET/CT).

The results of PET/CT of 913 patients (278 lymphoma; 635 solid tumors) were reviewed. The number, size, location and attenuation of all ASLMs, and spleen attenuation, were recorded. ASLM fluorodeoxyglucose uptake was graded as normal (less than or equal to that in the liver) or representative of malignancy (more than in the liver). Follow-up PET/CT in patients with ASLM was reviewed when available. ASLM size and attenuation for spleen and ASLM were compared by unpaired Student's t test. The χ(2) and Fisher's exact tests were used to compare ASLM frequency and uptake for lymphomatous and solid tumors, respectively.

ASLM frequency was 14.8%, with 152 ASLMs found in 135 patients. Mean attenuation was lower in ASLM compared with spleen by enhanced and non-enhanced CT (80.7 ± 20.4 HU vs 92.0 ± 14.4 HU, P < 0.0011 and 42.3 ± 9.0 HU vs 51.5 ± 6.3 HU, P < 0.0001, respectively). ASLM incidence was higher in lymphoma patients (56/278, 20.1%) than in those with solid tumors (56/278, 20.1% vs 79/635, 12.4%, P = 0.0036). Pathological uptake was found in four (7.1%) lymphoma patients but not in any patients with a solid tumor (P = 0.028) and it upstaged one patient with lymphoma. Follow-up PET/CT within 3-16 mo was available in 54% of patients with ASLM. Lesion regression was noted in all four pathological ASLMs on follow-up PET/CT after chemotherapy.

In patients with lymphoma, ASLM can represent malignancy, and thus further characterization with PET/CT might be warranted. Patients with neoplasia other than ASLM can be confidently diagnosed with accessory spleen.