Case presentation

A 41-year-old man with a medical history significant for Helicobacter pylori gastritis and hypertension initially presented in 2023 with progressive gynecomastia, ejaculatory dysfunction, and pelvic pain. These symptoms preceded the diagnosis of PMP and prompted endocrine and genitourinary evaluation. Initial evaluation included breast ultrasonography demonstrating possible breast masses, scrotal ultrasonography revealing bilateral epidermal cysts and a complex right hydrocele, and MRI of the abdomen and pelvis performed in January 2024, which was reported as unremarkable. The original MRI images were not available for review upon transfer; therefore, the reported findings could not be independently verified, and differences in imaging technique or interpretation cannot be excluded.

As the patient's symptoms progressed, contrast-enhanced CT of the abdomen and pelvis obtained in April 2024 demonstrated loculated ascites adjacent to the liver measuring 4.6 × 9.4 × 9.3 cm (Figure 1) and a soft tissue mass along the greater curvature of the stomach measuring 10.2 × 11.3 × 5.8 cm. By June 2024, he developed progressive abdominal distension secondary to ascites accompanied by unintentional weight loss.

Figure 1: Contrast-Enhanced CT Abdomen and Pelvis Demonstrating Loculated AscitesContrast-enhanced computed tomography (CT) of the abdomen and pelvis obtained in April 2024 demonstrating loculated ascites throughout the abdomen, including a large perihepatic fluid collection measuring 4.6 × 9.4 × 9.3 cm.

According to records obtained from the University Hospital of the West Indies, the patient underwent exploratory laparotomy in February 2025, during which the diagnosis of PMP was established. Intraoperative findings included extensive omental caking with tumor deposits involving the small bowel, peritoneum, and liver. Approximately 11 L of ascitic fluid were evacuated. Cytologic analysis of the ascitic fluid was positive for malignant cells, and an intraoperative biopsy demonstrated mucinous adenocarcinoma. However, the complete pathology report and original histologic slides from the outside institution were unavailable for review at the receiving institution.

Approximately five months after the initial diagnosis, the patient developed progressive respiratory symptoms. Three days before hospital day 1, CT angiography (CTA) of the chest demonstrated consolidation and collapse of the medial segment of the right middle lobe with small bilateral pleural effusions (Figure 2). Concurrent CT pulmonary angiography revealed mediastinal and hilar lymphadenopathy, bilateral loculated pleural effusions, and nodular soft tissue densities within the mediastinum and bilateral hilar. These imaging findings raised concern for thoracic extension of disease; however, subsequent pleural fluid cytology was negative for malignant cells, endobronchial ultrasound (EBUS) did not identify a suitable biopsy target, and pleural biopsy was not performed. Therefore, histologic confirmation of thoracic involvement was not obtained.

Figure 2: CT Angiogram of the Chest Demonstrating Right Middle Lobe Collapse and Bilateral Pleural EffusionsComputed tomography angiography (CTA) of the chest obtained three days before hospital day 1, demonstrating collapse and consolidation of the medial segment of the right middle lobe with small bilateral pleural effusions.

On hospital day 1, the patient re-presented to the University Hospital of the West Indies with worsening shortness of breath and a witnessed syncopal episode lasting approximately five minutes. He required emergent endotracheal intubation for airway protection in the setting of acute hypercapnic respiratory failure. At presentation, his Glasgow Coma Scale score was 3. Arterial blood gas analysis revealed a pH of 7.12, partial pressure of carbon dioxide (pCO₂) of 112.7 mmHg, and lactate level of 1.4 mmol/L. Respiratory cultures obtained on hospital day 2 grew Enterobacter bugandensis, which demonstrated susceptibility to gentamicin, piperacillin-tazobactam, and trimethoprim-sulfamethoxazole, and resistance to amoxicillin-clavulanate, ampicillin, and cefuroxime. The patient was treated with ceftriaxone and azithromycin.

Repeat CT imaging of the abdomen and pelvis obtained on hospital day 2 demonstrated persistent loculated ascites surrounding the liver measuring 5.4 × 9.3 × 10.8 cm, similar in appearance to prior imaging from April 2024; these imaging studies were not available upon transfer. Because of progressive disease and consideration for CRS-HIPEC, the patient was transferred to Arrowhead Regional Medical Center (ARMC) on hospital day 11 for further evaluation and management.

Upon arrival at ARMC, the patient was intubated, cachectic, and critically ill. Physical examination revealed a markedly distended abdomen, bilateral loculated pleural effusions, loculated ascites, and 1+ bilateral lower-extremity pitting edema. Laboratory evaluation demonstrated leukocytosis of 23.7 × 10⁹/L ( Figure 3). The patient was unable to tolerate spontaneous breathing trials because of persistently elevated peak inspiratory pressures.

Figure 3: Non-contrast CT Chest and Abdomen Demonstrating Bilateral Loculated Pleural EffusionsComputed tomography imaging demonstrating worsening bilateral loculated pleural effusions with largest component in the left pleural space, in the setting of advanced pseudomyxoma peritonei.

His hospital course was complicated by ventilator-associated pneumonia and persistent loculated pleural effusions. Initial blood cultures obtained on hospital day 11 demonstrated no growth. Subsequent respiratory cultures grew Enterobacter cloacae complex, while blood cultures obtained on hospital day 20 were positive for Serratia marcescens. Antimicrobial therapy included sequential treatment with cefepime and vancomycin, followed by piperacillin-tazobactam and meropenem. Clinical improvement was ultimately observed following completion of a one-week course of levofloxacin.

On hospital day 18, interventional radiology performed a left-sided thoracentesis and placed a pigtail drainage catheter within the right upper quadrant abdominal collection. Although fluid samples were successfully obtained, no solid tissue specimen could be collected. Cytologic analysis of the pleural and abdominal fluid collections was negative for malignant cells and therefore did not provide confirmatory tissue at the receiving institution despite the previously established diagnosis at the outside hospital. Repeat contrast-enhanced CT of the abdomen and pelvis obtained on hospital day 20 demonstrated the pigtail catheter within the right upper quadrant fluid collection and multiple perihepatic fluid collections without a suitable solid tissue target for biopsy (Figure 4).

Figure 4: CT of the Abdomen and Pelvis Demonstrating Loculated Ascites and Peritoneal Drain Placement(A) Axial contrast-enhanced CT of the abdomen and pelvis demonstrating a large perihepatic loculated ascitic collection. (B) Coronal contrast-enhanced CT of the abdomen and pelvis showing multiple loculated intra-abdominal fluid collections, with a pigtail drainage catheter in the right upper quadrant demonstrating minimal output.

EBUS performed on hospital day 23 failed to identify significant lymph node disease or suitable tissue targets for biopsy. Consultation with cardiothoracic surgery on hospital day 25 determined that pleural biopsy would carry substantial procedural risk with limited anticipated diagnostic benefit.

Because the complete outside pathology report and original histologic slides were unavailable for review following transfer, additional tissue sampling was pursued to confirm the diagnosis and further characterize the tumor. Thoracentesis, abdominal fluid drainage, and EBUS-guided sampling were nondiagnostic. Diagnostic laparoscopy was therefore performed on hospital day 30, demonstrating extensive peritoneal deposits and dense intra-abdominal adhesions, and the disease was considered surgically unresectable. Histopathologic evaluation demonstrated high-grade mucinous adenocarcinoma with signet-ring cells. Immunohistochemical staining demonstrated positivity for CK7, CK20, CDX2, and SATB2, supporting lower gastrointestinal differentiation (Figures 5-6). Esophagogastroduodenoscopy and colonoscopy performed in November 2024 did not identify a primary gastrointestinal malignancy. Although the immunophenotype supported lower gastrointestinal differentiation, a definitive primary tumor site could not be established based on the available clinical, operative, and pathologic findings.

Figure 5: Immunohistochemical Staining of the Peritoneal Lesion(A) Positive CDX2 staining and (B) positive SATB2 staining in the peritoneal lesion. The expression of CDX2 and SATB2 supports lower gastrointestinal differentiation of the high-grade mucinous adenocarcinoma.

Figure 6: Histopathologic Features of Pseudomyxoma Peritonei(A) Low-power (10×) and (B) high-power (20×) microscopic views showing abundant extracellular mucin pools characteristic of high-grade mucinous adenocarcinoma of the peritoneum.

Following multidisciplinary discussion regarding prognosis and treatment options, the patient elected to proceed with palliative systemic chemotherapy. He received one cycle of FOLFOXIRI (5-fluorouracil, leucovorin, oxaliplatin, and irinotecan) from hospital days 37-39. Bevacizumab was withheld because of concern for bowel perforation in the setting of extensive intra-abdominal disease. Although an additional cycle was considered, no further chemotherapy was administered because the patient remained ventilator-dependent, developed Enterobacterales and Serratia marcescens bacteremia requiring vasopressor support, and continued to experience progressive clinical deterioration.