Thoracic splenosis: a great mimic diagnosed by functional imaging

Abstract

Splenosis is defined as the heterotopic implantation of functional splenic tissue in extra-splenic compartments, usually secondary to traumatic or iatrogenic splenic rupture (1). Although it is most commonly found in the abdominal and pelvic cavities, implants have been reported in less common sites such as the thorax, liver, and subcutaneous tissue. Thoracic splenosis represents a diagnostic challenge, as it is usually an incidental finding, rarely symptomatic, and, from an imaging standpoint, can mimic malignant entities such as primary neoplasms or metastatic disease. We present two cases of splenosis diagnosed using nuclear medicine techniques, including the case of a 65-year-old woman with a history of gunshot wound, who required laparotomy, splenectomy, and left nephrectomy, in whom benign pleural and abdominal lesions were identified. Initial metabolic characterization using PET/CT and subsequent confirmation with 99mTc-HDRBC (Heat-Damaged Red Blood Cells) scintigraphy allowed us to establish the definitive diagnosis, avoiding unnecessary invasive procedures. Additionally, we describe a 58-year-old male with a history of blunt chest trauma and prostate cancer, in whom 18F-PSMA PET/CT suggested malignancy, but 99mTc-HDRBC scintigraphy confirmed multi-compartmental splenosis. This report highlights the importance of considering splenosis in the differential diagnosis of thoracic and abdominal nodular lesions in patients with a history of splenic trauma, as well as the value of functional imaging techniques in its accurate identification.

Key teaching points

• Thoracic splenosis should be suspected in patients with pleural nodules and prior splenic trauma.

• 99mTc-HDRBC (Heat-Damaged Red Blood Cells) scintigraphy is the gold standard for non-invasive diagnosis.

• Functional imaging prevents unnecessary invasive procedures.

Introduction

Splenosis is a benign acquired condition characterized by heterotopic autotransplantation of functional splenic tissue following splenic rupture, usually of traumatic or surgical origin. It manifests as single or multiple implants in various anatomical locations, predominantly in the abdominal and pelvic cavities. The mechanism involves the dissemination of splenic tissue fragments into the peritoneal cavity or, less frequently, into extra-abdominal locations such as the thorax, especially if there is concomitant diaphragmatic injury. The main causes are blunt abdominal trauma and splenectomy, which allow viable splenic tissue to be seeded in ectopic sites (Smoot et al. 2022).

Because in most cases it is asymptomatic and occurs incidentally, its true incidence is unknown; however, it has been estimated that up to 67% of patients with a history of splenic trauma may develop splenosis (Sánchez-Paniagua et al. 2016).

The diagnosis is based on clinical suspicion in cases of trauma or splenectomy and the identification of nodules with characteristics like those of the spleen in imaging studies. Historically, biopsy with histopathological confirmation has been considered the gold standard for diagnosis. However, as it is an invasive procedure with a potential risk of complications, its use is limited. In this context, scintigraphy with 99mTc-heat-damaged red blood cells (99mTc-HDRBC) has established itself as the diagnostic tool of choice, thanks to its high sensitivity and specificity, derived from the high uptake of heat-damaged erythrocytes by ectopic splenic tissue and minimal physiological hepatic uptake, compared to other nuclear imaging techniques (Sánchez-Paniagua et al. 2016). In complex cases, SPECT/CT may be necessary for better anatomical localization (Baldolli et al. 2017).

Thoracic splenosis is a rare form of this condition and usually presents as pleural or parenchymal nodules, posing a diagnostic challenge as it can mimic malignant processes. Similarly, intra-abdominal splenosis can be confused with liver neoplasms, gastrointestinal tract tumors, or mesothelioma (Vernuccio et al. 2020). Therefore, proper recognition of the patient’s traumatic and surgical history is essential to guide the diagnosis, allow for correct interpretation of imaging findings, and avoid unnecessary invasive studies or interventions.

Case presentation

A 65-year-old woman with a history of gunshot wound requiring exploration by laparotomy, splenectomy, and left nephrectomy. She presented with infectious symptoms, including cough, fever, and desaturation, and underwent a chest CT scan, which diagnosed pneumonia but also revealed nodular thickening of the left basal pleura and solid nodules in the peritoneum and lower left rib cage. Given the suspicion of neoplastic involvement, an 18F-FDG PET/CT scan was performed (Fig. 1), revealing pleural lesions with very low metabolism, suggesting a benign process. Due to the patient’s history of trauma, a possible diagnosis of splenosis was considered, which was confirmed by 99mTc-HDRBC scintigraphy (Fig. 2), with findings of high-intensity hyperactive foci in the left hemithorax and other smaller foci with uptake in the left hypochondrium, flanks, and iliac fossae; these scintigraphy signs were consistent with foci of splenosis.

Fig. 1.

65-year-old woman with post-traumatic thoracic splenosis. 18F-FDG PET/CT images. (A) Maximum intensity projection showing a focus with a slight increase in metabolism in the left chest wall (arrow). (B, C) Axial section in soft tissue fusion and simple window, at the level of the ninth left intercostal space, showing a nodular lesion of the wall involving the pleura and adjacent soft tissues with moderate metabolism (circle). (D, E) Coronal images in soft tissue fusion and simple window, showing nodularity in the lateral wall of the left chest wall with low to moderate metabolic activity (circle) corresponding to a focus of suspected thoracic splenosis

Fig. 2.

65-year-old woman with post-traumatic thoracic splenosis. Images from 99mTc-HDRBC scintigraphy. (A) Static image showing high intensity hyperactive foci at the base of the left hemithorax (circle) and other smaller foci with lower uptake in the left hypochondrium (orange arrow) and left iliac fossae (green arrow). (B-E) SPECT-CT images confirm focal hyperactive lesions in the left chest wall involving the pleura and soft tissues in the ninth intercostal space (thin arrows) (B, C) and others in the perihepatic (thick arrow) and supraumbilical (arrowhead) locations (D, E). The scintigraphic signs were consistent with thoracoabdominal splenosis

A 58-year-old man with a history of blunt chest trauma at age 25 that required splenectomy. During prostate cancer staging, an 18 F-PSMA PET/CT scan was performed (Fig. 3), documenting a primary lesion in the right peripheral zone of the prostate associated with lymph node metastases in the right external iliac chain and multiple blast lesions in the costal arches and pubic symphysis related to secondary involvement. However, multiple foci with abnormal increase in radiotracer uptake were documented in the peritoneum, periumbilical region, epigastrium, left renal fossa, and right parietocolic gutter, with lower SUVMax compared to secondary lesions, which, associated with the traumatic history, were considered possible foci of splenosis. A 99mTc-HDRBC scan (Fig. 4) was performed, showing multiple soft tissue density lesions distributed throughout the abdomen, with radiopharmaceutical uptake, confirming the presence of splenosis.

Fig. 3.

58-year-old man with post-traumatic splenosis. 99mTc-HDRBC scintigraphy images. (A, B) Static images showing high-intensity hyperactive focus with radiotracer uptake in the splenic bed (blue circle) (A) and in the mesogastrium (thin blue arrow) (B). (C-F) SPECT-CT images confirm focal hyperactive lesions with soft tissue density and radiopharmaceutical uptake in the splenic bed (thin white arrows) (C-D) and another lesion further down, immediately posterior to the paraumbilical abdominal wall (thick white arrow) with a smaller adjacent lesion further lateral (orange arrow) (E-F). The scintigraphy signs were consistent with thoracoabdominal splenosis

Fig. 4.

58-year-old man with post-traumatic splenosis. 99mTc-HDRBC scintigraphy images. (A, B) Static images showing high-intensity hyperactive foci with radiotracer uptake in the splenic bed (blue circle) (A) and in the mesogastrium (thin blue arrow) (B). (C-F) SPECT-CT images confirm hyperactive foci with soft tissue density and radiopharmaceutical uptake in the splenic bed (thin white arrows) (C-D) and another lesion further down, immediately posterior to the paraumbilical abdominal wall (thick white arrow) with a smaller adjacent lesion further lateral (orange arrow) (E-F). The scintigraphy signs were consistent with thoracoabdominal splenosis

Discussion

Splenosis is a relatively common complication after splenic rupture, usually secondary to trauma, which may go unnoticed in the acute phase and manifest years or even decades later. Its late presentation, together with atypical imaging findings, makes this entity a diagnostic challenge, especially when it is not considered in the differential diagnosis and can be confused with malignant or infectious pathologies.

Thoracic splenosis was first described in 1896 during an autopsy and represents a rare form of splenosis, with an approximate prevalence of 18% among patients with splenic rupture associated with diaphragmatic injury (Niu et al. 2018). Its pathogenesis is related to the spread of viable splenic tissue to the left hemithorax through diaphragmatic defects, where it most often implants in the parietal or visceral pleura, developing vascular supply from adjacent tissues and slowly evolving into mature functional splenic tissue (Lake et al. 2012; Vernuccio et al. 2020).

Clinically, thoracic splenosis is usually asymptomatic. In a review of 38 reported cases, only four patients presented respiratory symptoms, such as recurrent hemoptysis, productive cough, or pleuritic chest pain; all of them shared a history of thoracoabdominal trauma with splenectomy and exclusive involvement of the left hemithorax (Vernuccio et al. 2020). The average interval between trauma and diagnosis has been estimated at approximately 21 years, with a wide range between 3 and 45 years, with incidental findings being the most frequent scenario (Lake et al. 2012).

From an imaging perspective, thoracic splenosis can present as a solitary pulmonary nodule with pleural involvement in approximately 25% of cases, while the remaining 75% show multiple pulmonary or pleural nodules (Niu et al. 2018). These findings may mimic primary tumors, metastatic disease, or infectious processes, particularly when a detailed medical history is not available or the abdominal region is not evaluated to confirm the absence of the spleen (Lake et al. 2012).

When there is a high clinical suspicion, especially in patients with a history of splenic trauma and nodular findings in the left hemithorax, radionuclide imaging techniques play a key role in non-invasive diagnosis. In the cases presented, PET/CT with 18 F-FDG and 18 F-PSMA allowed for initial metabolic characterization of the lesions, revealing uptake patterns atypical for malignant disease. Subsequently, scintigraphy with 99mTc-HDRBC definitively confirmed the splenic nature of the implants, establishing itself as the diagnostic gold standard due to its high specificity and minimal physiological hepatic uptake compared to other nuclear medicine studies (Vernuccio et al. 2020; Malik et al. 2010; Romero Otero et al. 2018). Proper recognition of splenosis has important clinical implications, as it avoids unnecessary invasive procedures, such as biopsies or surgical resections, and prevents erroneous treatments targeting lesions suspected of malignancy. In most cases, management is conservative, given the benign nature of the entity and its possible partial contribution to splenic immune function. Surgical resection is reserved exclusively for symptomatic patients or those with complications, limited to the implants responsible for the clinical presentation (Smoot et al. 2022; Fremont and Rice 2007; Ferrer Marrero et al. 2017).

Conclusion

Thoracic splenosis is a rare benign entity that poses a significant diagnostic challenge due to its ability to mimic malignant processes on imaging studies. Its identification requires a high index of clinical suspicion, especially in patients with a history of splenic trauma and splenectomy.

Functional imaging techniques, particularly scintigraphy with 99mTc-HDRBC, allow a definitive diagnosis to be established noninvasively, avoiding unnecessary diagnostic and therapeutic procedures. Knowledge of this entity and its appropriate clinical and imaging correlation are essential for correct interpretation of the findings and appropriate management of the patient. Awareness of this entity is essential to avoid misdiagnosis and inappropriate oncologic management.

Author contribution

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Tatiana López Sandoval, Sebastián Peláez, Juan Carlos Ramirez and Carlos Caicedo Zamudio. The first draft of the manuscript was written by Tatiana López Sandoval, Juan Carlos Ramirez and Tatiana Cadavid, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

No funding was received for this study.

Data availability

This study is based on a narrative review of the literature and two illustrative clinical cases. No datasets were generated or analyzed during the current study. All relevant data are presented within the article.

Declarations

Informed consent

Informed consent was obtained from all individual participants included in the study.

Consent for publication

Written informed consent for publication of anonymized clinical information and imaging findings was obtained from the patients described in this study.

Conflict of interest

The authors declare that they have no conflict of interest.