Primary extrahepatic echinococcosis of the right lower abdomen

Introduction: Primary, intraperitoneal hydatidosis without involvement of the liver is a rare occurrence. Due to vague symptoms, echinococcosis is often neglected as a differential diagnosis. Case Report: We present a case of a primary extrahepatic echinoccocal cyst, located in the peritoneal cavity and in immediate contact to the right psoas muscle. After initial medical treatment, the cyst was surgically removed via laparotomy. Parts of the psoas muscle had to be removed due to muscle invasion and as the impairment of vena caval blood flow seemed imminent. Apart from a minor ventral thigh paraesthesia, the patient recovered well after surgery. Conclusion: Imaging and serologic tests are described as standard tools for diagnosing echinococcosis. Nevertheless, in uncertain cases, PCR analysis has proven to be useful. Conservative therapy of large intraabdominal echinococcal cysts has recently gained more interest. However, if the cyst is located in uncommon areas, surgery is the treatment of choice. Despite advanced imaging techniques, diagnosing intraabdominal extrahepatic echinococcosis to be quite challenging and should be included in the differential diagnosis of abdominal pathologies.


INTRODUCTION
The predominat forms of echinococcosis in humans are cystic echinococcosis (CE) and alveolar echinococcosis (AE). Primary infection of extrahepatic organs or structures is rare, so far only a few cases have been reported. The most common route of transmission for EC is oral transmission and requires two mammalian hosts. After ingestion of eggs and egg containing segments by a definitive host like dogs or an aberrant host like humans, the cystic metacestode develops in internal organs, preferentially in the liver [1,2].
Intraperitoneal hydatidosis is often difficult to diagnose, symptoms are vague and are seldom more specific like an anaphylactic reaction. However, in intraperitoneal hydatidosis severe complications are exceptional [3].
We present a case of intraabdominal CE without initial hepatic involvement in a 33yearold gardener.

CASE REPORT
We like to report a case of a 33yearold male with an indolent palpable mass of the right lower abdomen, initially suspected to be a teratoma. The patient did not recall any other irregularities, medical history did not disclose any serious illness.
Aside from a slight tenderness around the mass, physical examination did not reveal any abnormalities, Fever was absent and laboratory tests were normal.
Computed tomography and a previously performed ultrasound, both affirmed a single septate lesion, partly cystic, partly solid, without wall calcifications or daughter cysts. It measured approximately 20x12x11 cm. The inactive part was classified as WHO stage IV, the active part WHO stage II. The cyst was located in immediate contact to the psoas muscle. Other crucial structures seemingly were not affected ( Figure 1). There was no evidence of hydatidosis of the liver or the lung. Subsequently, a serologic test showed antibodies against EC, with a highly positive titre of 1:1684.
In cooperation with the department of infectiology, University Hospital Ulm, a therapy with escazole was started.
Unfortunately, medical treatment did not have any significant impact on the size of the mass. A six month follow up ultrasound and MRI only showed signs of regression. As the imaging results arose suspicion of involvement of vital structures within the lesion and the fact that the patient refused to take eskazole on a long term basis, it was decided to remove the cyst via laparotomy.
Intraoperatively, the tumor was extending up to the psoas muscle and the right kidney, already compromising the inferior vena cava. The distal part of the cyst was located within the muscle. Because of psoas muscle involvement small parts of the muscle had to be removed ( Figure 2). Histopathological examination confirmed an echinococcus granulosus cyst that has been fully extirpated without any scolices (Figure 3).
During the postoperative course the patient recovered well, neurologic examination did not reveal any loss of motor function. He reported ventral thigh paraesthesia which was compatible with affection of the lateral femoral cutaneous nerve due to bulky adhesions and muscle invasion in that area.
To present the risk of reinfection the patient was recommended to continue eskazole therapy for four weeks after the surgery.

DISCUSSION
Primary intraabdominal hydatidosis generally causes nonspecific symptoms like dull pain or a palpable mass with a variety of differential diagnoses [3,4]. In this case, the patient gave a short history of abdominal swelling without any obvious organ dysfunction. Although major complications are rare, rupture of an   intraperitoneal cyst due to trauma or increased pressure can be fatal, necessitating emergency surgery [5].
Despite advanced imaging techniques the cyst formation can be easily mistaken for other pathologies like abcesses or malignancies, especially when occurring at uncomon sites. Single cystic lesions are often difficult to distinguish from other peritoneal cysts like mesenteric cysts. Once diagnosed, ultrasonography seems to be a useful tool for follow up [6].
In our case radiologic imaging suggested an expanded teratoma. The CT scan showed a single heterogenous cyst with intracystic membranes. Typical attributes like wall attenuation, calcification or daughter cysts, were absent [7]. Since the patient did not show any signs of infection an abcess was ruled out. Due to the patient being a gardener by profession, a serological test was performed immediately to arrive at a quick diagnosis. However, the sensitivity of serology for ED varies, false negative results seem to occur more likely in cases with unusual locations. Under these circumstances PCR analysis has proved to be a useful dignostic method [8,9].
Although surgery is still the treatment of choice, percutaneous procedures have gained increasing interest and have been used successfully [10]. For EC at uncommon locations, however, surgery with complete cyst extraction accompanied by medical treatment is the preferred method [4,10].

CONCLUSION
In this case the positive serology lead quickly to a final diagnosis. Several authors reported the difficulties of relating the diverse clinical features to primary extrahepatic CE. In endemic areas or in patients with risk factors (farmers, gardeners) the possibilty of CE should be regarded as a differential diagnosis of abdominal pain and swelling. *********

Author Contributions
Ingeborg Bohlmann -Conception and design, Acquisition of data, Analysis and interpretation of data, Critical revision of the article, Final approval of the version to be published Johannes Zitt -Analysis and interpretation of dat, Critical revision of the article, Final approval of the version to be published Bertram Wagner -Analysis and interpretation of dat, Critical revision of the article, Final approval of the version to be published

Guarantor
The corresponding author is the guarantor of submission.