An unusual cause of mass in the shoulder: A primary hydatid cyst.

A hydatid cyst is a zoonotic infection which may affect any organ and tissue, particularly the liver and the lung. Primary muscular hydatid cysts comprise less than 0.7-3% of the cases. The hydatid cysts must be kept in mind to avoid a diagnostic puncture in cystic lesions to avoid the spreading of the disease. In this case report, we present an exceptionally rare case with an unusual localization of a primary hydatid cyst in the left deltoid muscle.

INTRODUCTION

A hydatid cyst is a zoonotic infection caused by the larval forms of mostly the Echinococcus granulosus.[123] It is endemic in Middle East and Mediterranean countries and the main host is predominantly dogs.[4] The location and the size of the cyst and the complications such as rupture and immunological reactions are the main source of patient's symptoms.[5] A hydatid cysts may affect any organ and tissue but the most common affected organs are the liver (60-70%) and the lungs (25-30%).[3] Primary muscular hydatid cysts comprise less than 0.7-3% of the cases.[67] The hydatid cysts must be kept in mind to avoid a diagnostic puncture in cystic lesions.

In this case report, we present an exceptionally rare case with an unusual localization of a primary hydatid cyst in the left deltoid muscle.

CASE REPORT

A 64-year-old man working as a farmer in a rural area was admitted to our hospital with a painless growing mass in his left shoulder. He noted the mass on the shoulder about 6 months ago and it grows slowly. As a farmer he has contact with sheep, dogs and cows. There was no history of abdominal pain, chest pain, hemoptysis, cough, fever, weight loss, urticaria or trauma [Figure 1]. Physical examination revealed a firm, nontender, semimobile mass of 10 × 8 cm in diameter on the posterolateral aspect of the left shoulder. There was no fluctuation, restriction of motion, erythema, ecchymosis or lymphadenopathy. The constant score of the patient was 88. An X-ray of the left shoulder revealed a mass without bone involvement. Ultrasonographic examination of the mass showed a big anechoic cyst in the left shoulder with a slightly thick wall which was involving small cystic areas measuring 10 × 7 cm in diameter. Magnetic resonance imaging (MRI) demonstrated a 10 × 7 × 5 cm diameter well-defined, encapsulated, soft tissue cystic lesion in the deltoid muscle. In the posterior part of the deltoid, there were multiple small cystic lesions inside the main cyst [Figure 2a–c]. Abdomen and chest CT showed no evidence of hepatic or pulmonary involvement, and the diagnosis of a primary muscular hydatid disease was made. Laboratory results showed a normal erythrocyte sedimentation rate, C-reactive protein and the echinococcal indirect hemaglutination (IHA).

Figure 1

There was a firm, non-tender mass of 10 × 8 cm in diameter on the posterolateral aspect of the shoulder

Figure 2

MRI aspects of T1 weighted axial image (a) and sagittal image (b) with fat suppression of the cyst, also T2-weighted coronal image shows the daughter cysts well (c)

Surgically, the mass was excised under general anesthesia with wide surgical margin with a posterolateral approach. The deltoid muscle in the margin of the mass was excised. The rotator cuff muscles were not affected. The mass was consisted with cysts and excised completely followed by irrigation with 3% hypertonic saline. The cysts were defined as mother and daughter cysts macroscopically [Figure 3]. Histological examination of the specimen also revealed mother and daughter cysts and fragments of the lamellar membrane of the hydatid cyst. Adjunctive albendazole treatment (400 mg/day) was prescribed for 3 months. The patient was symptom free after 2 years [Figure 4] and the shoulder function remained undisturbed (constant score was 88). There was no inferior subluxation due to deltoid insufficiency.

Figure 3

The mother and daughter cysts of the hydatid cyst were seen extracted in the surgery

Figure 4

The cyst was completely disappeared after 2 years on an axial T1-weighted scan

DISCUSSION

Hydatid disease is a parasitic infection caused by mainly Echinococcus granulosus. Dogs are the main hosts and the disease was transmitted to humans by the expelled eggs in the feces of the dogs.[123] A hydatid cyst is most frequently found in the liver and lungs, but can also be seen anywhere.[67] Primary muscular hydatid cysts were uncommon and usually located in the peripheral muscles such as supraspinatus, biceps brachii, pectoralis major, gracilis, psoas, sartorius and quadriceps have been reported in the literature.[678910111213] A hydatid cyst in the deltoid muscle was reported in two cases in the literature.[1415]

The main symptom is palpable swelling in muscular hydatid disease.[9] Contact with animals must be questioned in the history. Ultrasonography can be used in the diagnosis, but magnetic resonance imaging (MRI) is very useful and gave more information in the diagnosis.[1416] The multicystic appearance with homogenous intensity and the daughter vesicles are typical signs of a hydatid cyst in MRI. If the appearance of the ‘scolices’ was seen in the surgery, the diagnosis was confirmed.[3] If there was any suspicion of a hydatid cyst in the muscle, a diagnostic biopsy or aspiration must be avoided to prevent the spreading of the daughter vesicles.[317] Serologic tests can be used in the diagnosis and are valuable when they are positive, but half of the primary muscular hydatid cases gave a false-negative result as in our case. The indirect hemagglutination test (IHA) sensitivity rate has been reported as 67%.[1819]

The proposed treatment method in case of a muscular hydatid cyst is total surgical excision.[39] If the cyst is very large or the surgical procedure is difficult to completely excise, the main purpose is to prevent the spreading of the daughter vesicles to the surrounding tissues. Percutaneous cyst drainage, total excision of the germinative membrane, irrigation of the cyst pouch with scolicidal solution can be applied in this situation.[3918]3% hypertonic sodium chloride can be used as scolicidal solution.[2021] We excised the hydatid cyst completely in our case and also irrigated with 3% hypertonic solution.

Medical treatment of a hydatid cyst is not recommended alone, but can be used to prevent recurrence and spread of the disease after surgery.[22] We used albendazol for 3 months after surgery and no recurrence was seen.

As a conclusion, the hydatid cyst must be kept in mind in the differential diagnosis of soft tissue mass in the extremities, especially in regions where this zoonosis is endemic. The diagnosis can be made with the imaging techniques easily without performing a biopsy because of the risk of the contamination of the daughter cysts.