Surgical management and recurrence analysis in primary extrahepatic-extrapulmonary hydatid cysts: A single-center experience of 20 cases

Abstract

BACKGROUND

Primary extrahepatic-extrapulmonary hydatid cysts are rare and may present significant diagnostic challenges due to their atypical localization and similarity to benign or malignant cystic lesions.

AIM

To evaluate the clinical characteristics, surgical management, and recurrence outcomes of patients with primary extrahepatic-extrapulmonary hydatid cysts.

METHODS

A retrospective analysis was conducted on a total of 179 cases of hydatid cysts operated on between January 2015 and January 2026. Twenty primary cases without liver and lung involvement and with pathological confirmation were included in the study. Demographic, clinical, laboratory, and radiological data, as well as surgical methods, complications, and recurrence rates, were evaluated. The relationship between surgical technique and recurrence was analyzed using Fisher’s exact test.

RESULTS

Twelve of the patients (60%) were women and eight (40%) were men. The median age was 39.5 (18-75). The most frequent localization was intramuscular areas (25%). Total cyst excision was performed in 50% of cases, organ resection + total excision in 35%, and partial excision in 15%. The median follow-up period was 36.5 months (6-60). Recurrence was observed in two patients (10%). The recurrence rate was significantly higher in patients who underwent partial excision (P = 0.016). No mortality was observed.

CONCLUSION

Primary extrahepatic-extrapulmonary hydatid cyst is a rare but clinically significant condition. It should be considered in the differential diagnosis in endemic regions. Whenever feasible, total excision should be preferred; in cases where partial excision is performed, the risk of recurrence should be considered.

Key Words: Hydatid cyst; Extrahepatic; Extrapulmonary; Surgery; Recurrence

Core Tip: Primary extrahepatic-extrapulmonary hydatid cysts are rare and may present significant diagnostic challenges because they can mimic benign or malignant cystic lesions. In this retrospective cohort study of 20 primary cases, we evaluated clinical characteristics and surgical outcomes. Our findings demonstrate that recurrence occurred only in patients who underwent partial cyst excision. These results highlight the importance of complete surgical excision whenever feasible to minimize recurrence risk. Surgeons should consider hydatid cyst in the differential diagnosis of atypical cystic lesions in endemic regions.

INTRODUCTION

Hydatid cyst is a zoonotic infection caused by the larval form of Echinococcus granulosus and is endemic particularly in the Mediterranean basin, the Middle East and Central Asia[1,2]. Due to the physiological filtration mechanism of the oncospheres participating in the portal circulation, the disease is most frequently observed in the liver (50%-75%) and lungs (10%-30%)[3]. Extrahepatic and extrapulmonary localizations are rare and have been reported at a rate of 7%-19% in the literature[4,5]. Primary extrahepatic-extrapulmonary involvement is quite rare, and its pathogenesis is not fully understood. Hematogenous and lymphatic spread theories and the hypothesis of secondary placement after involution of the primary focus are put forward[6-8]. These atypical localizations present diagnostic challenges as they can clinically mimic benign or malignant cystic lesions. In this study, the clinical and surgical outcomes of primary extrahepatic-extrapulmonary hydatid cyst cases operated on in a single center were evaluated considering the literature and reported in accordance with the STROBE guidelines. Most publications in the literature are at the case report level, and the number of large series systematically evaluating primary extrahepatic-extrapulmonary involvement is limited. This study aims to contribute to the literature with its series of 20 primary cases.

MATERIALS AND METHODS

A retrospective analysis was conducted on 179 cases of hydatid cysts operated on between January 2015 and January 2026. Twenty primary cases without liver and lung involvement were included in the study.

Inclusion criteria: Absence of hepatic and pulmonary involvement, no prior history of treatment for hydatid cyst disease, pathologically confirmed hydatid cyst.

Evaluated parameters: Age, sex, residence (rural/urban), animal contact, presenting complaints, localization and cyst size, diagnostic method, laboratory and serological tests, American Society of Anesthesiologists (ASA) score, surgical technique, length of hospital stay, complications, follow-up duration, recurrence. Eosinophilia was defined as > 500/µL. Total IgE levels > 100 IU/mL were considered elevated. Indirect hemagglutination (IHA) titers ≥ 1:320 were considered positive. All patients underwent ultrasonography. Computed tomography (CT) was preferred for solid organ involvement, while magnetic resonance imaging was preferred for soft tissue involvement. Pulmonary involvement was excluded based on chest radiography. In our institution, albendazole therapy was standardized for all patients with a preoperative diagnosis of hydatid cyst based on radiological findings and/or positive serological tests.

During surgery, the operative field around the cyst was isolated with gauze pads soaked in hypertonic saline. Hypertonic saline was used as the scolicidal agent. Depending on the localization, total cyst excision, partial excision with drainage, or organ resection was performed. In our institution, albendazole therapy was standardized for all patients with a preoperative diagnosis of hydatid cyst based on radiological findings and/or positive serological tests. Patients with a preoperative diagnosis received albendazole (10 mg/kg/day) for two months before surgery and for at least two months postoperatively. However, patients in whom the diagnosis was established intraoperatively did not receive preoperative albendazole therapy.

Statistical analysis

Statistical analysis of the data was performed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk, NY, United States). The distribution of continuous variables was assessed using the Shapiro-Wilk test. Non-normally distributed data were presented as median (minimum-maximum) or median (IQR), and categorical variables were presented as n (%). The relationship between continuous variables was evaluated using Spearman correlation analysis. The association between surgical technique and recurrence was analyzed using Fisher’s exact test. A P value < 0.05 was considered statistically significant.

This study was approved by the Research Application Review and Evaluation Commission of the Mersin Provincial Health Directorate, Republic of Türkiye Ministry of Health (decision No. 6; date: 02.04.2021). The study was conducted in accordance with the principles of the Declaration of Helsinki.

RESULTS

Twelve patients (60%) were female and eight (40%) were male. The median age was 39.5 years (18-75). Sixty-five percent of the patients lived in rural areas, and 45% had animal contact. The median duration of symptoms (time to hospital presentation) was 2 months (IQR: 1-3; 1-12). No significant relationship was found between duration of symptoms and cyst diameter (spearman ρ = -0.06, P = 0.80). This finding indicates that time to presentation is not a significant parameter in predicting cyst size. Demographic and clinical characteristics are summarized in Table 1.

Table 1 Demographic and clinical characteristics, n (%).

Variable	Value
Age (median, min-max)	39.5 (18-75)
Female	12 (60)
Male	8 (40)
Rural residence	13 (65)
Animal contact	9 (45)
Symptom-to-presentation time (months), median (IQR; min-max)	2 (1-3; 1-12)
Length of hospital stay (days), median (IQR; min-max)	3 (2-5.25; 1-17)
Eosinophilia	5 (25)
Elevated IgE	5 (25)
Positive IHA	10 (50)
ASA I/II/III	8 (40)/10 (50)/2 (10)
Symptoms
Abdominal pain	10 (50)
Pelvic pain	4 (20)
Palpable mass (including thigh/hip)	4 (20)
Nausea-vomiting	1 (5)
Back pain	1 (5)

IHA: Indirect hemagglutination; ASA: American Society of Anesthesiologists; IQR: Interquartile range.

Sixty-five percent of the patients lived in rural areas. The most common presenting complaint was localized pain. Pelvic pain was the predominant symptom in pelvic localizations, whereas swelling and pain were more prominent in intramuscular localizations. No ruptured cysts were detected in any of the patients. The most frequent localization was intramuscular areas (25%). Other localizations included the spleen, pancreas, omentum, and retroperitoneal region. The average cyst diameter was 8.3 cm (3-17 cm), and all patients had a single cyst. The localization distribution is shown in Table 2. Example radiological images of atypical localizations are presented in Figure 1. No significant differences were found in serological positivity, complication rate, and length of hospital stay when comparing gastrointestinal localizations (pancreas, mesentery, omentum, gallbladder) with other localizations (P > 0.05). The comparison between gastrointestinal-related localizations (pancreas, mesentery, omentum, gallbladder) and other localizations was performed as an exploratory post-hoc analysis and should be interpreted with caution due to the small sample size.

Figure 1 Axial contrast-enhanced computed tomography images demonstrating rare extrahepatic and extrapulmonary hydatid cyst localizations. A: A well-defined hypodense cystic lesion located within the right adrenal gland (arrow), without evidence of adjacent organ invasion; B: A round, homogeneous cystic mass in the presacral/retrovesical pelvic compartment (arrow), producing mild mass effect on surrounding structures; C: A well-circumscribed unilocular cystic lesion adjacent to the right iliopsoas muscle (arrow), without calcification or daughter cyst formation.

Table 2 Distribution of extrahepatic-extrapulmonary hydatid cyst localizations.

Localization	n (%)
Intramuscular	5 (25)
Spleen	2 (10)
Pancreas	2 (10)
Omentum	2 (10)
Retroperitoneum	2 (10)
Ovary	2 (10)
Mesentery	1 (5)
Adrenal	1 (5)
Gallbladder	1 (5)
Pelvis	1 (5)
Thigh	1 (5)

In laboratory evaluation, eosinophilia was detected in 25% of patients, elevated IgE in 25%, and positive IHA in 50%. As surgical treatment, organ resection plus total excision was performed in 7 patients (35%), total cyst excision in 10 patients (50%), and partial excision with drainage in 3 patients (15%) (Table 3). Although the median length of hospital stay was longer in patients who underwent partial excision, the difference was not statistically significant (P > 0.05).

Table 3 Surgical procedures and postoperative outcomes.

Surgical procedure	n (%)
Total cyst excision	10 (50)
Organ resection + total cyst excision	7 (35)
Partial excision + drainage	3 (15)

In the postoperative period, 2 patients developed wound infection, 1 patient had femoral nerve damage, and 1 patient had bleeding. One patient with a large intramuscular hydatid cyst located in the proximal thigh developed temporary femoral nerve injury related to surgical dissection. The neurological deficit improved during follow-up without permanent sequelae. No mortality was observed. Although cyst diameter was higher in patients who developed complications, no statistically significant relationship was found (P > 0.05). The median follow-up period was 36.5 months (IQR: 31.25-45.25). Recurrence occurred in two patients (10%). Both patients initially underwent partial excision. The relationship between partial excision and recurrence was found to be statistically significant (P = 0.016) (Table 4). No significant association was found between ASA groups (ASA III vs ASA I-II) and the development of complications (Fisher’s exact test, P = 1.00).

Table 4 Surgical technique vs recurrence.

Surgical technique	Recurrence (+)	Recurrence (-)
Partial excision	2	1
Others	0	17

Fisher’s exact test: P = 0.016.

DISCUSSION

Hydatid cyst is among the zoonotic infections neglected by the World Health Organization and is a significant public health problem, especially in endemic regions[1,2] and continues to be seen endemically[9]. The disease develops in intermediate hosts (sheep, goats, cattle, horses, deer and mice) that feed on food contaminated with parasite eggs released into the external environment through the feces of definitive hosts (dogs, wolves and foxes) and is transmitted to humans through the digestive or respiratory route via these intermediate hosts[10]. Due to physiological filtration of oncospheres entering the portal circulation, the liver (50%-75%) and lungs (10%-30%) are the most involved organs[3]. Therefore, localizations outside the liver and lungs are considered rare. In the literature, the rate of rare localization has been reported to be between 7%-19%[4,5]. In our study, the primary extrahepatic-extrapulmonary ratio was 11.2%, which is consistent with the literature. Furthermore, the unique aspect of our study is that all cases were primary and hepatic and pulmonary involvement was excluded by systemic imaging. This study demonstrates that primary extrahepatic-extrapulmonary hydatid cyst is a rare but clinically significant condition.

Since Davis first reported renal hydatid cyst in 1702 and Bertelot first reported splenic hydatid cyst in 1790, it has been known that the disease can affect a wide variety of places in the body besides the liver and lungs[11]. Extrahepatic-extrapulmonary hydatid cysts either develop secondarily because of spontaneous or traumatic perforation of a hydatid cyst located in another organ, or they develop primarily without any focus in other organs. Primary extrahepatic-extrapulmonary hydatid cyst is quite rare and is found incidentally[7]. According to the hematogenous dissemination theory, scolicices entering the systemic venous circulation from the gastrointestinal tract and passing through the hepatic and pulmonary filters rarely reach the arterial circulation; therefore, involvement of other sites is uncommon. The lymphatic dissemination theory, on the other hand, suggests passage through the thoracic duct via the intestinal lymphatic system. In Deve’s classical theory, secondary localization occurs following involution of an overlooked primary focus[6-8]. In our series, all patients underwent detailed radiological scanning, and no concurrent hepatic or pulmonary focus was detected. This supports a primary localization.

The fact that 65% of our patients live in rural areas and 45% have contact with animals is consistent with epidemiological studies reported in endemic regions. The HERACLES study revealed a higher prevalence in rural areas. These findings show that the disease is a problem that has not only a surgical aspect but also a public health aspect[12].

In our series, the most common localization was intramuscular involvement (25%). Although muscle tissue is considered unfavorable for the parasite due to its contractility and lactic acid environment, primary localization can occur, albeit rarely[13]. Pancreatic, adrenal, gallbladder, and retroperitoneal localizations are mostly reported in the literature at the case report level. Therefore, this series of 20 cases makes a significant contribution to the literature.

The sensitivity of serological tests decreases in extrahepatic localizations[14]. In our series, IHA positivity was 50%, which is consistent with the literature. Therefore, radiological methods play a decisive role in diagnosis. While ultrasonography is the first step, CT and magnetic resonance imaging are more valuable for deeply located lesions. The fact that the diagnosis was only made peroperatively in two patients illustrates the diagnostic difficulties of atypical localizations. In the differential diagnosis, primary and secondary benign and malignant cystic, semisolid, and solid pathologies, pseudocysts, metastatic masses, and abscesses should be considered[15].

Extrahepatic-extrapulmonary hydatid cyst cases can mimic malignant cystic or solid tumors depending on their localization. In cystic lesions, particularly those located in the pancreas, ovaries, retroperitoneal space, and adrenal glands, cystic neoplasms, metastatic masses, and primary malignant tumors are primarily considered in the differential diagnosis. This may lead to inappropriate treatment and unnecessary surgical interventions in the preoperative period. In cystic lesions, particularly those located in the pancreatic or ovarian regions, unnecessary and extensive resections may be performed due to suspicion of malignancy, which can increase morbidity. In endemic regions, considering the possibility of hydatid cyst in the evaluation of atypical cystic lesions is important both for appropriate surgery and for preventing the risk of intraoperative rupture and anaphylaxis[16,17].

The goal in the treatment of extrahepatic-extrapulmonary hydatid cysts should be to prevent infection, rupture to adjacent organs, and anaphylaxis. Treatment options include medical therapy, percutaneous drainage, and surgery[18]. Surgery is the mainstay of treatment for extrahepatic-extrapulmonary hydatid cyst disease[18]. The goal is to achieve total excision while preserving the integrity of the cyst. In our series, total excision was performed in 50% of cases, organ resection in 35%, and partial excision in 15%. The significantly higher recurrence rate in patients who underwent partial excision (P = 0.016) indicates that total excision should be preferred whenever possible. In the three patients who underwent partial excision, complete cyst removal was not feasible due to the close relationship with critical anatomical structures or dense adhesions to surrounding tissues. In one case, intraoperative diagnostic uncertainty also contributed to the surgical decision. Recurrence rates reported in the literature range from 3%-26%[19]. Our rate of 10% is within an acceptable range. Our complication rate was low, and no mortality was observed. Especially in retroperitoneal and intramuscular localizations, the technical challenges of surgery should be considered. This complication was observed in a case with proximity to the femoral neurovascular structures, highlighting the technical challenges of surgery in atypical anatomical locations.

The limitations of this study include its retrospective design, single-center experience, and limited sample size. Despite these limitations, a series of 20 primary cases is remarkably large in the literature. The subgroup analysis between gastrointestinal and non-gastrointestinal localizations did not reveal significant differences in outcomes, although these findings should be interpreted cautiously due to the limited sample size.

CONCLUSION

Primary extrahepatic-extrapulmonary hydatid cyst, although rare, should always be considered in the differential diagnosis in endemic regions. Atypical localizations require careful clinical and radiological evaluation as they can mimic benign or malignant cystic lesions. Serological tests may have limited sensitivity; therefore, imaging methods are crucial for diagnosis. Surgery is the primary treatment approach, and total cyst excision should be preferred whenever possible. It should be considered that the risk of recurrence may increase in cases where partial excision is performed.