Presentation Patterns, Diagnostic Modalities, Management Strategies, and Clinical Outcomes in Patients with Hydatid Disease of the Pelvic Bone: A Comparative Review of 31 Cases

Hydatid disease is a parasitic zoonosis commonly caused by Echinococcus granulosus. It characteristically involves the liver and the lungs but rare occurrences in other organs have also been reported. Bone involvement is distinctly uncommon, which is predominantly a silent and slowly progressive disease with a long latent period. We conducted a systematic literature search of MEDLINE, Cochrane, Embase, and Scopus databases. After a comprehensive review of the search results, a total of 31 cases of hydatid disease of the pelvic bone fulfilled the inclusion criteria. The data on patient demographics, epidemiology, lesion site, management, clinical outcomes, and follow-up were collected and analyzed. This review illustrates that hydatid disease should be considered among the differential diagnoses of unusual cystic lesions of the pelvic bone. Prompt diagnosis and appropriate management are of paramount importance to prevent bone destruction and serious complications in these patients. Long-term follow-up should be performed for potential recurrence.


Introduction And Background
Human hydatid disease, also known as cystic echinococcosis, is most commonly caused by Echinococcus granulosus. The lesions of this infectious etiology can be encountered in myriad body locations. While it frequently involves the liver and the lungs, bone involvement is exceedingly rare [1,2]. Although the incidence of bone disease is remarkably low, its diagnosis and management can be challenging. The clinical presentation of patients with osseous hydatid disease is frequently nonspecific. Occasionally, pain and pathological fractures are the presenting symptoms [3,4]. In regard to the diagnosis, the findings of clinical history, laboratory studies, radiologic investigations, and histopathologic analysis play a key role [5,6]. Surgical resection of the cystic lesions with antihelminthic chemotherapy is the treatment of choice. Bone curettage, achieving the negative resection margins, is essentially important to avoid the recurrence of the disease [7]. The prognosis is usually favorable but early treatment may save the patients from inadvertent events as well as excessive surgical debridement requiring bone replacement [8]. The aim of this comparative review was to summarize the data on clinical presentations, diagnostic strategies, management options, and the clinical outcomes in patients with pelvic bone hydatidosis. This paper emphasizes that the clinicians should be vigilant for this disease, particularly in patients presenting with nonspecific skeletal symptoms.

Materials and methods
We conducted a systematic literature search to retrieve published data on pelvic bone hydatidosis using the MEDLINE, Cochrane, Embase, and Scopus databases. Several controlled vocabulary search terms (medical subject headings [MeSH] and Embase subject headings [Emtree]), terminologies like "hydatid disease," "bone," "pelvis," "pelvic involvement," and "management" were combined using the Boolean operators "AND" and "OR" with the terms "hydatidosis," "outcome," and "chemotherapy." The search was conducted without a defined time filter, with language limitation to English-only articles. Additionally, a manual search was also performed using the bibliography of all accessed publications through the abovementioned search strategy. We initially screened all retrieved titles and abstracts to determine their relevance to our topic. The same protocol was used to screen the selected articles for full texts to check their relevance.

Results
A total of 127 studies were initially obtained, consisting of but not limited to original articles, case series, and case reports. After excluding 49 duplicate articles, 78 papers were thoroughly studied. The articles available in any language other than the English were excluded from the review. Thirty-two papers were found relevant to the scope of our study but 15 studies were found accessible in order to retrieve pertinent data required for this review [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The total number of patients in this comparative review was 31 as some case studies consisted of more than one patients. The data on individual cases of pelvic bone hydatidosis on patient demographics, locations of the lesions, management, and clinical outcomes are summarized (  A comprehensive review of these cases indicated a slight female predominance (female, n = 17; male, n = 14). The mean age of patients was 47 years (range: 14-77 years). According to our analysis, ilium (n = 21) was the most frequent lesion site followed by acetabulum (n = 7), pubis (n = 6), ischium (n = 5) and sacrum (n = 5). In a few patients, concurrent involvement of the long bones like femur and/or soft-tissue structures of the pelvis was also noticed.

Epidemiology
According to one estimate, the incidence of bone involvement has been described to range from 0.5% to 4% of all cases of hydatidosis [24]. The bone disease predominantly involves the spine, which is encountered in approximately 50% to 60% of the cases, followed by the femur, tibia, humerus, skull, and ribs. With regard to geographical distribution, hydatid disease is globally distributed, especially in the north and northwestern China, parts of South America, East Africa, Australia, Central Asia, North Africa, Russia, Western Europe, and southern United States [24]. The highest prevalence is noted in rural areas where animals are slaughtered. In the recent past, several hydatid elimination programmes had been implemented, with varying degrees of success. Recently, hydatid vaccine has also been considered to combat this crippling infestation.

Pathogenesis
Although the bone is an uncommon location for hematogenous dissemination of hydatid disease, the presence of the lesions has frequently been reported. The progression of the disease takes place either due to the formation of diverticula or exogenous vesiculation. This disease ensues destructive pathological osseous sequels predominantly by three mechanisms: a) the cyst that increases in size gradually compresses the adjacent tissues, eventually causing compression-related bone atrophy, b) occasionally, the hydatid cyst may obstruct the vessels entering the bones through nutrient foramina causing ischemia, c) the cells like osteoclasts, proliferate around the infectious focus of hydatidosis. On the contrary, the extraosseous invasion culminates in the bone disruption that subsequently may lead to pathologic fracture of the involved portions of the bone [24].

Clinical presentation
The clinical presentation of bone hydatidosis is frequently varied. It is notable that the bone involvement is largely a silent disorder that has the propensity to remain dormant for decades. Pain, swelling, walking abnormalities, sinus tract formation, ambiguous abdominal pain, or compressive manifestations are among the symptoms and signs of this disease. In patients with hydatidosis of pelvis involving the lumbosacral neural plexus, sciatica becomes the first clinical symptom. Similarly, a vast majority of patients initially present with late complications of this disease like a pathologic fracture, neurological deficits, infected cyst or fistula formation [24]. The physical examination is mostly inconclusive for abnormalities. However, in rare instances, changes in the limb symmetry, abscess or fistula formation or vertebral deformation can be deciphered. Individuals like sheepherders, veterinarians, or butchers are particularly prone to this infection. Therefore, this disease warrants awareness and updated knowledge on part of clinicians, especially in endemic areas when patients present with generalized musculoskeletal complaints.

Diagnosis
The diagnosis of pelvic bone hydatidosis frequently poses a challenge as pelvic localization by radiological modalities may be difficult and clinical features are mostly nonspecific. Although serological testing has gained importance recently, their sensitivity and specificity is not 100% [25]. Computed tomography is an excellent modality to detect osseous hydatidosis. The radiologic investigations often demonstrate multiple expanding lesions with no defined margins. The lesions may assume a classic waffle appearance due to extensive osteolysis [26]. The unique pathogenetic changes encountered in this disease lead to weakening of the cortical bone, without any periosteal reaction. Magnetic resonance imaging has also been used to investigate the regional disease extent, especially soft-tissue involvement. The hydatid lesions appear as a hyposignal in T1-weighted images and a hypersignal in T2-weighted images [27]. In these patients, a whole-body scan is performed in order to assess the concurrent involvement of other organ systems. As the diagnostic dilemma is frequently noted, tuberculosis, malignancy, aneurysms, and metastatic lesions should be excluded based on the standard set of investigations [27]. A definitive diagnosis is established on the basis of histopathologic examination of the biopsy and/or resected specimen.

Management
In terms of management, hydatid disease of the pelvic bone is particularly a serious clinicopathologic entity as the cyst in this location may invade pelvic joints, which can potentially make complete recovery difficult. Although the definitive treatment of bony hydatidosis is surgery, a number of studies have highlighted the combination of antihelminthic chemotherapy and surgery as a feasible choice [28]. In the published medical literature, several surgical methods, including simple drainage or debridement, complete excision, total hip arthroplasty, bone grafting, femoropubic arthrodesis, megaprosthetic replacement, massive arthroplasty, osteosynthesis, and hemipelvectomy have been reported thus far [29].
The procedure of simple drainage or debridement is commonly employed; however, early recurrence and inadvertent disease dissemination may occur due to incomplete removal. In this technique, the lesion is exposed while adjoining normal structures are protected with the use of 20% NaCl solution. The burnishing of the inner walls of the lesion cavity is also important to avoid recurrence of the disease. This method is mostly used in patients where cystic echinococcosis cannot be excluded preoperatively [29]. Furthermore, bone cement filling is a reliable option to avoid the relapse of the cystic lesions due to its ability to kill the daughter cysts due to necrotizing effects of increased temperature in the polymerizing cement [30]. Several surgical methods are used for reconstruction of osseous portions affected by the hydatidosis. A pedicle screw-rod system is an effective reconstructive option with no need for extensive preoperative feasibility assessment but it may present a dilemma while treating joint involvement. Partial excision of the cystic lesions followed by joint arthroplasty is a good method in this regard [18]. Similarly, megaprosthetic replacement may also help to restore acceptable limb functionality [10]. The major goal of these procedures is to restore the limb function rather than complete eradication of the infectious etiology due to echinococcosis. The use of liquid nitrogen carries several benefits; however, its role in disinfection of bony Echinococcus cysts has rarely been documented. However, Liang et al. supported the notion that bony cystic lesions due to E. granulosus maybe enervated by utilizing liquid nitrogen for a time period of 20 minutes [20].
The therapeutic strategy for hydatid disease with bone involvement resembles oncologic therapy compared to the surgical treatment of visceral hydatidosis [24]. In these patients, a combination of preoperative antihelminthic chemotherapy, surgery, and postoperative antihelminthic chemotherapy demonstrates promising outcomes. Before surgical intervention, medical therapy, mostly consisting of albendazole, targets the cyst size reduction and limits the infectious process. In the post-operative setting, it is primarily used for the treatment of potentially undetectable cysts, ultimately avoiding the recurrence. Similarly, irradiation can be used in patients who cannot tolerate the chemotherapy and/or in inoperable disease [31].

Prognosis
The prognosis of hydatid disease of the pelvic bone largely depends on its bony extensions. In cases with a widespread disease demonstrating an involvement of the pelvic joints and long bones, the prognosis is generally poor. These patients are particularly prone to life-threatening sepsis. Furthermore, if the disease involves several muscle groups or muscle layers, the prognosis is not good and it poses a significant therapeutic challenge due to the presence of sinus and/or fistula formation [32]. In the light of these observations, early diagnosis of pelvic bone hydatidosis is critically important as a late detection makes it a difficult-to-treat disease [33].

Conclusions
Although pelvic bone hydatidosis is rare, a high index of clinical suspicion should be maintained for this disease, especially in endemic areas. These patients may pose a diagnostic challenge due to nonspecific clinical presentation. The radiological characteristics of the hydatid cyst often suggest the pathology but a definitive diagnosis can only be made by histopathologic examination. Early diagnosis is of paramount importance for the bone salvage and to avoid complications. The treatment of choice is a combination of chemotherapy and surgical debridement. Meticulous technical preparation is necessary as surgery of the pelvis is relatively difficult and incomplete resection of the cyst may culminate in recurrence. The present paper highlights the importance of early detection of the pelvic bone hydatidosis followed by efficient management for a good clinical outcome.