Splenosis mimicking prostate cancer recurrence

A 62-year-old male patient with a history of radical retropubic prostatectomy for prostate adenocarcinoma 15 years prior was referred for radiologic evaluation of a palpable left-upper abdominal mass. Past medical history was significant for splenic rupture and splenectomy following a motor vehicle accident 46 years earlier.

An abdominal computed tomography (CT) scan without contrast demonstrated a ventral fat-containing hernia; however, incidentally on CT was a left-upper quadrant (LUQ) soft-tissue density and an irregular 5.7 x 2.3 x 3.3cm soft-tissue density in the rectovesical space (Fig. 1). Technetium-99m sulfur colloid scintigraphy showed radiotracer uptake in the LUQ and rectovesical space, suggesting a diagnosis of splenosis (Fig. 2).

In our patient with past prostate cancer status post-prostatectomy, the primary concern for a rectovesical mass was recurrence of malignancy. The LUQ mass was presumed to be an accessory spleen. Follow-up prostate-specific antigen levels were negligible. Positron emission tomography/CT did not demonstrate increased metabolic activity of the rectovesical mass. Given the history of splenic trauma, splenosis was considered and supported by the technetium-99m sulfur colloid scintigraphy. Rectovesical mass biopsy confirmed the presence of splenic tissue. The patient was reassured that the LUQ and rectovesical masses were benign and received no treatment to remove the splenic implants since the patient was asymptomatic.

Splenosis refers to the implantation of splenic tissue, most commonly by direct extension in the peritoneal cavity, following splenic trauma due to rupture or abdominal surgery. Splenosis of the peritoneal cavity following splenic trauma is estimated between 26% to 66%. [1,2] Patients are typically asymptomatic, and splenosis is usually incidentally found on imaging or during laparotomy. However, splenosis can also be a mimicker of malignancy on imaging and prompt an extensive work-up.

Technitium-99m sulfur colloid scintigraphy is a technique that identifies cells of the reticuloendothelial system (RES), including the bone marrow, liver, and spleen. This imaging modality was the first diagnostic tool utilised to diagnose splenosis. The radiolabeled colloid does not collect in the bladder; as such, the pelvic mass labeled with the lower arrow in Fig. 2 is of RES origin and does not represent the bladder. In the clinical context of our patient with a history of splenic trauma, this mass is a splenule. Technetium-99m heat-damaged erythrocyte scintigraphy is a more sensitive diagnostic tool for splenosis. [3] This imaging modality is the pre-operative diagnostic gold standard for diagnosing splenosis; however, it is less readily available than technitium-99m sulfur colloid scintigraphy.

Surgical management is not recommended in a patient with asymptomatic splenosis. Biopsy is rarely needed to diagnose splenosis once technetium-99m scintigraphy identifies the splenules. In the context of our patient who had a history of prostate cancer, a biopsy of the rectovesical mass was taken and confirmed the presence of splenic tissue. However, given the patient’s negligible PSA level, negative PET/CT, and positive technetium-99m sulfur colloid scan, it would have been reasonable to spare the patient from invasive diagnostic testing.

Written informed patient consent for publication has been obtained.