A rare case of primary retroperitoneal mucinous cystadenocarcinoma presenting with recurrent infected psoas abscess

Abstract

Introduction and significance:

Retroperitoneal mucinous adenocarcinoma is a rare malignancy, typically presenting with nonspecific symptoms leading to delay in diagnosis and treatment.

Case presentation:

A 53-year-old man patient was seen with debilitating pain in the right thigh and reduced mobility, following 1 year of recurrent psoas abscesses. The physical exam revealed a mass in the right flank and a positive psoas sign. The laboratory work revealed elevated alkaline phosphatase and carcinoembryonic antigen (CEA), with decreased hemoglobin and creatine phosphokinase. Imaging revealed a large heterogeneous retroperitoneal mass (25.88 × 17.44 × 17.26 cm) compressing adjacent structures. Drainage was mucinous in nature; histopathology revealed well-differentiated mucinous adenocarcinoma with cytokeratin positivity. Escherichia coli infection proved secondary contamination from gastrointestinal sources. Antibiotics, analgesics, and interval drainage were administered to the patient. Chemotherapy was considered but later contraindicated with the onset of renal failure. The patient was placed on palliative care with symptomatic improvement.

Clinical discussion:

This case highlights the diagnostic difficulty of retroperitoneal mucinous adenocarcinoma, especially when occulted by infection and nonspecific presentation. The secondary infection and massive size of the tumor contribute to the difficulty in diagnosis and treatment.

Conclusion:

Early detection through thorough assessment is paramount. Multidisciplinary management is indicated, although such complications as renal failure may interfere with treatment and decrease prognosis.

Introduction

Primary retroperitoneal mucinous cystadenocarcinoma (PRMC) is an extremely rare tumor, the pathogenesis of which remains unclear and controversial. Because of the rarity of these tumors, it is hard to determine their exact origin and proper treatment. According to some authors, the tumor arises in heterotopic ovarian tissue^[1]. PRMC is exceptionally rare, with fewer than 30 cases published in the literature to date. This tumor originates in the retroperitoneal space, lacking any connection to the ovaries, pancreas, or other intra-abdominal organs, which makes its diagnosis and management particularly challenging. PRMC is believed to arise from ectopic ovarian tissue or pluripotent mesothelial cells that undergo mucinous differentiation, although its exact pathogenesis remains unclear^[2].

Clinically, PRMC may present with nonspecific symptoms such as abdominal pain, a palpable mass, or gastrointestinal disturbances, depending on its size and location^[3]. However, the presence of a recurrent infected psoas abscess as an initial manifestation is exceedingly uncommon. Psoas abscesses are typically secondary to direct extension of infection from nearby structures or hematogenous spread and are rarely associated with primary malignancies^[4]. The management of PRMC involves a combination of surgical resection and, in some cases, adjuvant chemotherapy or radiotherapy, depending on the stage and histological grade of the tumor. Due to the rarity of PRMC, there is limited consensus on optimal treatment protocols, and the prognosis can vary widely. Early diagnosis and complete surgical excision remain the most crucial factors in improving outcomes for affected patients^[5]. Patients with mucinous adenocarcinoma had a poorer survival rate, with a 3-year overall survival of 67.5%. This indicates that patients with mucinous adenocarcinoma had a lower chance of surviving for 3 years after treatment compared to those with non-mucinous adenocarcinoma. The difference in survival was statistically significant (P < 0.001)^[6]. In univariate analysis, several risk factors for invasive mucinous adenocarcinoma (IMA) were identified, including gender, age, TNM stage, smoking history, lymph node and pleural metastasis, spread through air spaces, tumor size, pathological grade, and specific computed tomography (CT) findings. Spiculated margin sign was found to be a protective factor. In multivariate analysis, key risk factors included smoking history, lymph node metastasis, pathological grade, tumor size, and pneumonia-type CT signs. There was no significant association between epidermal growth factor receptor mutations, anaplastic lymphoma kinase mutations, lobulated margin, or air bronchogram with IMA prognosis^[7].

Case presentation

A 53-year-old man presented with severe right thigh pain and inability to walk for 10 days, with fever for 7 days. He had two prior surgeries for psoas abscess drainage in the past year. No history of trauma, radiculopathy, paresthesia, weakness, weight loss, abdominal pain, gastrointestinal or urinary symptoms, alcohol, or drug use. Examination showed the lower limb in flexion and external rotation, a tender 9 × 7 cm swelling in the right flank, and a positive psoas sign. Given his clinical history and presentation, differential diagnoses included psoas abscess secondary to septic arthritis of the hip, osteomyelitis of the spine, and retroperitoneal tumors. Tuberculosis (TB) was also considered, given its endemicity and frequent association with psoas abscesses. However, the absence of systemic TB symptoms (chronic cough, night sweats, and weight loss) and the presence of mucinous fluid in prior drainage procedures shifted the focus toward a neoplastic etiology. Other potential conditions such as renal abscess, iliopsoas bursitis, and pyelonephritis were also evaluated. Laboratory findings (Table 1) showed elevated alkaline phosphatase and carcinoembryonic antigen (CEA), with low levels of chloride, creatine phosphokinase, bilirubin, and hemoglobin. The abscess was drained through a posterior incision (Fig. 1). The drained material was mucinous in nature and was sent for microbiological and histopathological analysis. The patient was started on intravenous medications, including cefoperazone (1000 mg) and sulbactam (500 mg) injections, metronidazole (500 mg) injection, ketorolac tromethamine (30 mg) injection, and omeprazole (40 mg) injection. The culture report revealed Escherichia coli as the causative organism, suggesting that the infection might have originated in the gastrointestinal tract. A specimen of brownish, jelly-like material measuring 5 × 5 cm was sent for histopathological examination. Microsections revealed a nucleoplasm composed of sheets and nests of atypical cells with hyperchromatic nuclei, set against a background of abundant mucin. Immunohistochemistry showed positivity for cytokeratins, confirming the diagnosis of well-differentiated mucinous adenocarcinoma. The pathological differential included mucinous cystadenoma, metastatic mucinous carcinoma, and pseudomyxoma peritonei, which were ruled out based on histological and clinical findings.

HIGHLIGHTS

• Primary retroperitoneal mucinous cystadenocarcinoma (PRMC) is a very rare tumor, originating from the retroperitoneal space alone and not in relation to ovarian or other intra-abdominal organs.

• Clinical presentation is often overshadowed by nonspecific presentation of abdominal pain and palpable masses; however, presentation as a first recurrent infected psoas abscess is very unusual.

• Diagnosis is challenging due to rarity and nonspecific imaging features; histopathological examination and immunohistochemistry are essential to establish.

• Treatment is most often by surgical removal; however, adjuvant chemotherapy has an uncertain role due to limited data.

• Prognosis is unpredictable; early diagnosis and complete surgical resection are crucial to improve results.

Table 1.

Laboratory diagnosis

Test	Result	Reference range
Chloride	95.1	98–106 mmol/L
Creatine phosphokinase	23.2	60–190 U/L
Bilirubin	0.323	0.3–1.2 mg/dl
Alanine aminotransferase	11.2	4–42 U/L
Alkaline phosphatase	172	40–130 U/L
Urea	23.8	13–43 mg/dl
Creatinine	1.10	0.6–1.3 mg/dl
Sodium	138.3	136–146 mEq/L
Potassium	4.43	3.5–5.1 mEq/L
Calcium	9.23	8.4–10.2 mg/dl
Carcinoembryonic antigen	8868	<3 ng/ml
Hemoglobin	9	12–15 g/dl
Neutrophils	80	40%–60%

Figure 1.

Postoperative surgical site image showing abscess drainage performed via a posterior incision.

A CT scan revealed a heterogeneous attenuation area occupying the right hemiabdomen, with varying degrees of attenuation. A contrast-enhancing nodular area with soft tissue attenuation and multiple septations were also noted. This area measured approximately 25.88 × 17.44 × 17.26 cm (Fig. 2A). The upper margin extended to the lower renal pole, causing the right kidney to be pushed supero-anteriorly. The medial margin reached the midline and contained multiple small air loculi (Fig. 2B). A significant mass effect of the mucinous mass on adjacent abdominal viscera was observed. No metastases and lymphadenopathy were observed, and no identifiable primary origin of the tumor was found (Fig. 2C). Having an advanced stage of mucinous retroperitoneal adenocarcinoma with such an excessive size of more than 10 cm, he was told to undergo chemotherapy. Before initiating chemotherapy, renal function assessment was performed due to the high risk of nephrotoxicity associated with cytotoxic agents, particularly platinum-based drugs (e.g., oxaliplatin), which can cause cumulative renal damage. The 99mTc-DTPA renal scan revealed markedly reduced bilateral renal function, with the right kidney more severely affected. The scan showed patchy perfusion, diminished uptake, large cold areas, and minimal excretion in the right kidney, while the left kidney had slow excretion but homogeneous radiotracer uptake. The calculated glomerular filtration rate (GFR) was significantly reduced (16.25 ml/min for the left kidney and 18.76 ml/min for the right kidney), indicating substantial renal impairment.

Figure 2.

Radiological images of the abdomen and pelvis. (A) A large retroperitoneal mass involving the abdominal wall, characterized by necrotic tissue with solid and cystic areas, causes displacement of the bowel to the left side. (B) Extension of the retroperitoneal mass into the pelvis, abutting the iliac crest and lateral pelvic wall. (C) No hepatic metastases or involvement of other accessory structures.

Consequently, systemic chemotherapy was withheld, and the patient was shifted to palliative management focusing on symptomatic relief, nutritional support, and periodic tumor drainage to manage mass effect symptoms. Regular follow-up was planned to reassess renal function and determine future treatment feasibility. Thereafter, an arrangement for regular follow-up will be made so as to keep track of treatment response and address complications if any arise in the future. Despite supportive care and palliative management, the patient’s condition deteriorated due to progressive disease and renal failure. Unfortunately, he succumbed to his illness.

Discussion

To diagnose a primary retroperitoneal mucinous cystadenocarcinoma is rare and difficult; usually for an individual to present with signs that are attributed to more common diseases, such as infections or trauma. However, there was this 53-year-old male with severe pain in his right thigh and a background history of multiple psoas abscesses, which is not typical of tumors located in the retroperitoneum. In cases like the one presented here, despite the fact that most psoas abscesses are linked with tuberculosis or septic arthritis, they may also result from advanced cancers, including sarcomas found in the spongy tissue of kidneys; these tumors include the mucinous adenocarcinomas^[8,9].

The remarkable levels of CEA in this patient were noteworthy because the CEA is an infamous tumor marker that is often increased across a number of malignant diseases, such as mucinous adenocarcinomas^[10]. However, although it is not specific to a single malignancy, its elevation can help with the diagnosis and monitoring of treatment responses^[11]. CT scans showing large retroperitoneal mass with mixed densities and containing several septa are consistent with mucinous cystadenocarcinomas, which have complicated imaging features and may also cause the displacement of adjacent organs^[12,13]. In view of the size and extent of tumor growth, a thorough management plan involving chemotherapy needed to be instituted.

A well-differentiated mucinous adenocarcinoma, confirmed by positive cytokeratin staining, exhibits histopathological findings that are in line with the imaging and clinical presentation. Mucinous cystadenocarcinomas possess abundant mucinous stroma and atypical cells such that sometimes they can be confused with other tumor types^[14,15].

Chemotherapy for PRMC is not well established due to its rarity. However, regimens used for mucinous tumors of the gastrointestinal or ovarian origin are often applied. Oxaliplatin with 5-Fluorouracil (5-FU) is commonly used, while paclitaxel-based regimens (such as 5-FU + paclitaxel or carboplatin + paclitaxel) have shown some efficacy in reported cases^[16]. Previously reported cases of PRMC involved complete surgical resection without rupture. In one case, a 32-year-old woman underwent tumor excision and adjuvant chemotherapy, remaining recurrence-free for 42 months. Another case, the first reported in English literature involving a male patient, described a 64-year-old man with a 24 × 20 × 16 cm³ cystic tumor, which was resected intact and showed strong immunohistochemical staining patterns similar to ovarian mucinous tumors^[2,17].

In contrast, our case differed significantly, as only abscess drainage was performed rather than complete tumor resection. This presents a diagnostic challenge, as the drained abscess may be a manifestation of an underlying mucinous adenocarcinoma. The lack of tumor resection limits comprehensive histopathological assessment, emphasizing the need for heightened clinical suspicion.

Conclusion

In this extremely rare case of PRMC presenting as recurrent psoas abscesses, management required a collaborative treatment strategy, including surgical drainage, chemotherapy considerations, and radiological interventions. Although the prognosis was poor due to the advanced stage of the tumor, the treatment strategy was aimed at controlling disease progression and improving quality of life. However, renal impairment posed a significant challenge, ultimately limiting systemic chemotherapy options. This case underscores the importance of considering PRMC in the differential diagnosis of recurrent psoas abscesses, especially in patients with atypical presentations. Clinicians should maintain a high index of suspicion and employ a thorough diagnostic workup, including imaging and histopathology, to avoid delays in diagnosis. A coordinated medical approach involving oncologists, radiologists, and surgeons is essential to optimize patient outcomes. Early identification of treatment-limiting factors, such as renal dysfunction, is crucial for tailoring appropriate management strategies. Future studies on PRMC could help establish standardized treatment guidelines and improve patient outcomes.

Ethical approval

Ethical approval was not required.

Consent

Written consent has been obtained from the patient for the use of images and his personal details for the purpose of this publication and can be made available to the Editor-in-chief if required.

Sources of funding

None.

Author contributions

H.M.H.: conceptualization, supervision, data curation, methodology, writing – original draft, writing – review & editing. N.U.K.: conceptualization, data curation, methodology, writing – original draft, writing – review & editing. M.D.T.: data curation, investigation, writing – original draft, writing – review & editing. M.M.M.: conceptualization, investigation, data curation, writing – original draft. A.A.A.: conceptualization, supervision, writing – original draft, writing – review & editing. U.S.: conceptualization, supervision, writing – original draft, writing – review & editing.

Conflicts of interest disclosure

The authors report no conflict of interest.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Hafiz Muhammad Hamza.

Provenance and peer review

None.

Data availability statement

Not applicable.

Assistance with the study

None.