Abdominal and pelvic splenosis: atypical findings, pitfalls, and mimics

The Peritoneum: Anatomy, Pathologic Findings, and Patterns of Disease Spread

Disease spread in the abdomen and pelvis generally occurs in a predictable pattern in relation to anatomic landmarks and fascial planes. Anatomically, the abdominopelvic cavity is subdivided into several smaller spaces or compartments by key ligaments and fascial planes. The abdominal cavity has been traditionally divided into peritoneal, retroperitoneal, and pelvic extraperitoneal spaces. Recently, more clinically relevant classifications have evolved. Many pathologic conditions affect the abdominal cavity, including traumatic, inflammatory, infectious, and neoplastic processes. These abnormalities can extend beyond their sites of origin through various pathways. Identifying the origin of a disease process is the first step in formulating a differential diagnosis and ultimately reaching a final diagnosis. Pathologic conditions differ in terms of pathways of disease spread. For example, simple fluid tracks along fascial planes, respecting anatomic boundaries, while fluid from acute necrotizing pancreatitis can destroy fascial planes, resulting in transfascial spread without regard for anatomic landmarks. Furthermore, neoplastic processes can spread through multiple pathways, with a propensity for spread to noncontiguous sites. When the origin of a disease process is not readily apparent, recognizing the spread pattern can allow the radiologist to work backward and ultimately arrive at the site or source of pathogenesis. As such, a cohesive understanding of the peritoneal anatomy, the typical organ or site of origin for a disease process, and the corresponding pattern of disease spread is critical not only for initial diagnosis but also for establishing a road map for staging, anticipating further disease spread, guiding search patterns and report checklists, determining prognosis, and tailoring appropriate follow-up imaging studies. ©RSNA, 2024 Supplemental material is available for this article.

Spleen regeneration after subcutaneous heterotopic autotransplantation in a mouse model

BACKGROUND

Splenectomy may lead to severe postoperative complications, including sepsis and cancers. A possible solution to this problem is heterotopic autotransplantation of the spleen. Splenic autografts rapidly restore the regular splenic microanatomy in model animals. However, the functional competence of such regenerated autografts in terms of lympho- and hematopoietic capacity remains uncertain. Therefore, this study aimed to monitor the dynamics of B and T lymphocyte populations, the monocyte-macrophage system, and megakaryocytopoiesis in murine splenic autografts.

METHODS

The model of subcutaneous splenic engraftment was implemented in C57Bl male mice. Cell sources of functional recovery were studied using heterotopic transplantations from B10-GFP donors to C57Bl recipients. The cellular composition dynamics were studied by immunohistochemistry and flow cytometry. Expression of regulatory genes at mRNA and protein levels was assessed by real-time PCR and Western blot, respectively.

RESULTS

Characteristic splenic architecture is restored within 30 days post-transplantation, consistent with other studies. The monocyte-macrophage system, megakaryocytes, and B lymphocytes show the highest rates, whereas the functional recovery of T cells takes longer. Cross-strain splenic engraftments using B10-GFP donors indicate the recipient-derived cell sources of the recovery. Transplantations of scaffolds populated with splenic stromal cells or without them afforded no restoration of the characteristic splenic architecture.

CONCLUSIONS

Allogeneic subcutaneous transplantation of splenic fragments in a mouse model leads to their structural recovery within 30 days, with full reconstitution of the monocyte-macrophage, megakaryocyte and B lymphocyte populations. The circulating hematopoietic cells provide the likely source for the cell composition recovery.

The Role of the Spleen in Portal Hypertension

As liver disease progresses, intrahepatic vascular resistance increases (backward flow theory of portal hypertension) and collateral veins develop. Adequate portal hypertension is required to maintain portal flow into the liver through an increase in blood flow into the portal venous system (forward flow theory of portal hypertension). The splenic artery resistance index is significantly and selectively elevated in cirrhotic patients. In portal hypertension, a local hyperdynamic state occurs around the spleen. Splenomegaly is associated with a poor prognosis in cirrhosis and is caused by spleen congestion and by enlargement and hyperactivation of splenic lymphoid tissue. Hypersplenism can lead to thrombocytopenia caused by increased sequestering and breakdown of platelets in the spleen. The close relationship between the spleen and liver is reflected in the concept of the hepatosplenic axis. The spleen is a regulatory organ that maintains portal flow into the liver and is the key organ in the forward flow theory of portal hypertension. This review summarizes the literature on the role of the spleen in portal hypertension.

Primary splenic lymphoma on top of intrahepatic splenosis: A unique case report

Solid organ splenosis is a challenging diagnosis with many atypical imaging features that can overlap with neoplastic masses of the affected organ. We present a sporadic case of intrahepatic splenosis in a 68-year-old woman with transformation into a low-grade B cell lymphoma. Initial cross-sectional imaging suggested focal nodular hyperplasia (FNH) ruled out on contrast-enhanced Magnetic Resonance Imaging (MRI) using a hepatobiliary-specific contrast agent. A Tc-99m sulfur colloid scan was negative. The final diagnosis was confirmed by a needle-guided biopsy revealing intrahepatic splenosis with transformation into a low-grade B cell lymphoma.

Spleen: Reparative Regeneration and Influence on Liver

This review considers experimental findings on splenic repair, obtained in two types of small animal (mouse, rat, and rabbit) models: splenic resections and autologous transplantations of splenic tissue. Resection experiments indicate that the spleen is able to regenerate, though not necessarily to the initial volume. The recovery lasts one month and preserves the architecture, albeit with an increase in the relative volume of lymphoid follicles. The renovated tissues, however, exhibit skewed functional profiles; notably, the decreased production of antibodies and the low cytotoxic activity of T cells, consistent with the decline of T-dependent zones and prolonged reduction in T cell numbers. Species-specific differences are evident as well, with the post-repair organ mass deficiency most pronounced in rabbit models. Autotransplantations of splenic material are of particular clinical interest, as the procedure can possibly mitigate the development of post-splenectomy syndrome. Under these conditions, regeneration lasts 1-2 months, depending on the species. The transplants effectively destroy senescent erythrocytes, assist in microbial clearance, and produce antibodies, thus averting sepsis and bacterial pneumonia. Meanwhile, cellular sources of splenic recovery in such models remain obscure, as well as the time required for T and B cell number reconstitution.