Large abdominal wall and intraperitoneal pseudocysts: a diagnosis of exclusion that still requires the scalpel

Cystic and cystic-appearing masses of the peritoneal cavity and abdominal wall remain among the more troublesome categories in abdominal diagnosis, precisely because their imaging appearances overlap so extensively. A unilocular collection with a thickened, enhancing wall can correspond to a mesenteric or omental cyst, an enteric duplication cyst, a lymphangioma, a mucinous neoplasm, or a postoperative fluid collection, and cross-sectional imaging frequently cannot separate these entities with confidence (1,2). The widely used de Perrot classification of mesenteric and omental cysts captures this heterogeneity by sorting such lesions into lymphatic, mesothelial, enteric, urogenital, mature cystic teratoma, and non-pancreatic pseudocyst categories, the last of which is explicitly the residual group that lacks any epithelial lining (3). Radiologic-pathologic reviews of abdominal and pelvic cystic lesions reach the same practical conclusion: imaging narrows the differential but rarely closes it, and final classification often depends on histology (4,5). Among these entities, the non-pancreatic pseudocyst occupies an awkward position: it is benign, it has no epithelial lining, and it is defined largely by what it is not. These lesions are genuinely rare—mesenteric and omental cysts of all types occur in the order of 1 per 100,000 to 250,000 hospital admissions, and pseudocysts are only a fraction of that group—so most clinicians will encounter very few over a career, and the published experience is correspondingly thin. The clinically relevant problem is that the features clinicians would normally rely on to triage an abdominal mass—size, vascularity, adherence to bowel, and aspiration cytology—are least informative in exactly these lesions. The result is a recurring scenario in which a large abdominal mass cannot be confidently characterized short of resection, while the literature guiding that decision consists almost entirely of isolated case reports.

In this issue of AME Case Reports, Jhaveri and colleagues report a 73-year-old man with obesity and prior abdominal surgery in whom a 21-cm left lower-quadrant mass was discovered incidentally during evaluation for a ureteral stone (6). The lesion was highly vascular and intimately adherent to both the abdominal wall and the colon. Two percutaneous sampling attempts yielded only hemorrhagic debris and nonspecific cytology, and imaging could not exclude a neoplasm. At operation, roughly 2 months after presentation, the cyst required painstaking dissection from bowel and fascia, evacuation of approximately 3 liters of fluid, and was complicated by two inadvertent enterotomies that were repaired primarily. Final pathology showed a chronic, fibrotic, non-epithelialized pseudocyst, with retained suture material identified at the fascial margin as a plausible nidus for chronic inflammation.

The novelty here is not the existence of a non-pancreatic pseudocyst, which has been described in the mesentery, omentum, and retroperitoneum (2,7,8), but rather the convergence of several features in a single lesion: an unusually large abdominal-wall-centered collection, marked hypervascularity arising from the rectus musculature, dense colonic adherence, and a documented foreign-body trigger. Most reported giant non-pancreatic pseudocysts are intraperitoneal or retroperitoneal; an abdominal-wall-centered lesion of this size is decidedly less common, although a multiloculated intraperitoneal pseudocyst has been reported in a man with prior inguinal hernia repair, and abdominal-wall pseudocysts have followed incisional hernia mesh repair (9,10). Earlier reports and institutional series have tended to emphasize either the diagnostic difficulty or the operative difficulty in isolation (7,11). This case is informative because it links the two: the same chronic inflammatory process that rendered aspiration uninformative also obliterated the tissue planes that made resection hazardous. In that sense, the report adds a coherent mechanistic thread linking nondiagnostic sampling to intraoperative morbidity, which is more useful to the practicing surgeon than either observation alone.

It is worth dwelling on why the preoperative imaging was so unhelpful, because the pattern is instructive beyond this single patient. On cross-sectional imaging, a non-pancreatic pseudocyst typically appears as a unilocular collection with a thick, enhancing wall, an appearance it shares with a long list of benign and malignant entities; the de Perrot scheme and radiologic-pathologic reviews both stress that wall thickness, septation, and enhancement do not map cleanly onto histology (3-5). Two features in this case actively pulled the differential toward something more sinister: the lesion’s prominent vascular supply from the rectus musculature and its dense adherence to colon. In a lesion this large, those findings could plausibly indicate a sarcoma, a gastrointestinal stromal tumor, or a mucinous neoplasm with peritoneal involvement, and they cannot be dismissed on imaging alone. The location added a further trap. A predominantly abdominal-wall mass invites consideration of a desmoid tumor, an organizing hematoma, or a chronic seroma after hernia repair, yet at operation the lesion proved more intimately related to the colon than the radiographs had suggested—a reminder that the apparent compartment of origin on imaging is itself unreliable in these chronic, plane-effacing lesions (9,10). The practical message is not that imaging is useless but that, for this class of lesion, it should be read as defining operative anatomy and resectability rather than as conferring a tissue diagnosis.

The proposed pathogenesis is biologically coherent. A pseudocyst lacks an epithelial lining and is, by definition, an organized collection walled off by fibrous and granulation tissue (1). In a patient with prior small-bowel resection and hernia repair, retained suture material can sustain a low-grade foreign-body reaction; non-absorbable suture is well documented to provoke chronic granulomatous inflammation, and retained surgical material has produced inflammatory pseudotumors years after the index operation (12,13). Repeated micro-hemorrhage into a confined space, followed by incomplete resorption and progressive fibrosis, provides a credible route from a small collection to a giant encapsulated mass, a sequence also invoked to explain the abdominal pseudocysts that arise around ventriculoperitoneal shunt catheters (14,15). This also explains the two findings that might otherwise seem contradictory—a benign lesion that is nonetheless densely vascular and adherent. Hypervascularity reflects the chronic reparative response rather than neoplastic angiogenesis: organizing granulation tissue is richly vascular by nature, and a wall that has remodeled over months to years can recruit a vigorous blood supply from neighboring muscle, which is exactly what was seen arising from the rectus here. This is why vascularity on imaging cannot be taken as evidence of malignancy, and why histology, rather than imaging, is required to settle the question (2).

The report has clear strengths. It documents the full diagnostic pathway, including two failed aspirations, and is candid about the intraoperative complications rather than presenting an idealized course—candor that is consistent with the transparency the CARE framework was designed to encourage (16). The limitations are equally worth stating plainly. As a single case, it cannot establish how often abdominal-wall pseudocysts behave this way, and the existing evidence base—dominated by individual reports and small institutional series—does not permit reliable estimates of incidence, recurrence, or complication rates (11). Cyst-fluid biochemistry and tumor markers were not obtained, and histopathologic images were unavailable, so the characterization rests on the descriptive pathology report. Consent could not be obtained from the patient. None of these undermines the central message, but they do limit how far the case can be generalized, and they highlight measurements—particularly cyst-fluid analysis—that future reports should capture prospectively.

For the clinician, two practical points follow. First, the limited value of fine-needle aspiration in this setting is predictable rather than incidental. Because a pseudocyst has no epithelium to sample, aspirates yield blood, fibrin, and macrophages that resemble an organizing hematoma and cannot exclude a mucinous neoplasm; the same diagnostic ceiling has been documented even for pancreatic cystic lesions, where cytology and cyst-fluid markers are more standardized (17,18). A nondiagnostic aspirate should therefore not be falsely reassuring. In pancreatic cystic disease, carcinoembryonic antigen, amylase, and increasingly molecular testing for KRAS and GNAS mutations have given cyst-fluid analysis some discriminatory power; no comparable validated panel exists for non-pancreatic abdominal pseudocysts, which is one reason resection rather than sampling remains the route to diagnosis (17,18). Second, the operative lesson is that a benign histology does not predict a benign operation. Decompression of a giant cyst to improve exposure is a reasonable maneuver, but dense adherence to bowel means enterotomy is a foreseeable risk for which the surgical team should be prepared. These are observations to weigh in planning, not rules to apply mechanically.

The operative narrative repays a closer reading, because the two inadvertent enterotomies were not simply bad luck. In a densely fibrotic lesion that has effaced the plane between cyst wall and bowel, the surgeon is often dissecting through scar in which the colonic wall and the pseudocyst capsule are indistinguishable by inspection or palpation. The literature on giant non-pancreatic and mesenteric pseudocysts repeatedly describes the same difficulty, and reported series have required en-bloc bowel resection or have settled for marsupialization when the posterior wall could not be safely freed from the mesenteric root or great vessels (7,11,19). Decompression helps by reducing tension and improving exposure, but it does not recreate the lost plane and may, by collapsing the cyst, make the residual wall harder to distinguish from adjacent viscera. Several practical implications follow that the report illustrates rather than prescribes: counseling the patient preoperatively about the genuine possibility of bowel resection; ensuring colonic preparation and a surgeon comfortable with primary repair or anastomosis; considering ureteric identification when the lesion abuts the retroperitoneum; and maintaining a low threshold to convert from a minimally invasive to an open approach when planes cannot be developed safely. Where the lesion is more favorably situated and less adherent, laparoscopic enucleation has been performed with low morbidity, but that option narrows as adherence and vascularity increase (19-21). The candor of this report in documenting both injuries is therefore useful precisely because it sets a realistic expectation for what resection of such a lesion entails.

Stepping back, the broader value of a report like this lies in how it reframes a familiar clinical reflex. The instinct when faced with an indeterminate cystic mass is to sample it, and when sampling fails, to sample again; this case shows why that instinct can mislead, since a second nondiagnostic aspirate consumed time and offered nothing that altered management. For an abdominal-wall or intraperitoneal collection with a thick wall and no convincing benign explanation, the decision that matters is whether the lesion needs to come out, and for most large or symptomatic lesions in which malignancy cannot be excluded the answer is yes—complete excision is endorsed across the non-pancreatic pseudocyst literature both to obtain a diagnosis and to forestall complications such as rebleeding, infection, rupture, obstruction, and fistulization (7,8,22). Framing the operation this way, as a resection planned from the outset rather than as an escalation reached only after diagnostics fail, also changes the consent conversation and the operative preparation in ways this case makes concrete. The patient recovered well despite the two enterotomies, which is reassuring, but the better-prepared operation is the one that anticipates them. That is the most transferable lesson here: in a giant, chronically inflamed pseudocyst, the diagnostic and operative difficulties are two faces of the same pathology, and recognizing that early lets the team plan for the resection the lesion was always going to require.

Several questions merit attention going forward. Whether decompression-first or en-bloc resection minimizes injury when bowel is encased is unresolved and unlikely to be answered by single cases; a pooled analysis of reported non-pancreatic pseudocysts, with standardized reporting of size, vascularity, adherence, and complications, would be more instructive than further isolated reports (7,11). Where anatomy permits, a laparoscopic approach has been used to define tissue planes, enucleate the lesion, and limit collateral injury, and its role relative to open excision in large, adherent lesions deserves systematic comparison (19-21). Routine collection of cyst-fluid biochemistry and, where feasible, molecular markers would help clarify how reliably these lesions can be distinguished preoperatively from mucinous neoplasms, and image-guided drainage alone is recognized to be inadequate when the wall cannot be excised and malignancy has not been excluded (22). Until such data accumulate, the pseudocyst will remain a diagnosis of exclusion, and complete surgical excision will remain both the definitive diagnostic step and the curative one—a position this report supports without overstating it.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, AME Case Reports. The article did not undergo external peer review.

Funding: None.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0189/coif). K.T. receives an annual research grant from Godo Shigen Co., Ltd.; this company is engaged in iodine production and has no financial interest in the subject matter or materials discussed in this manuscript. The author has no other conflicts of interest to declare.

Ethical Statement: The author is accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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