**3. Pathology**

#### **3.1. Cyst structure**

Morphologically, hydatid cyst consists of three layers and hydatid fluid. The first is the avascular outer pericystic layer or adventitia which is the host tissue formed by the lung as a reaction to the foreign body (parasite) (Fig 2). The other two layers, the laminated mem‐ brane (external layer of the cyst) or the ectocyst laminated membrane is an acellular laminar mucopolysaccaride layer and the germinative layer (inner layer of the cyst), or endocyst lay‐ er that gives rise to larval scolices (Fig 3).

The cyst fluid resembles water in appearance which may contain daughter vesicles. The cysts exist in different forms: intact or ruptured, single or multiple, unilateral or bilateral, solely located in the lung or concomitantly in other organ lodgements (especially in the liver).

Thoracic Hydatid Cyst: Clinical Presentation, Radiological Features and Surgical Treatment http://dx.doi.org/10.5772/53533 197

**Figure 2.** operative specimen: adventitia which is the host tissue formed by the lung as a reaction to the foreign body (white arrow) and de germinative membrane ( black arrow); E Boeykens, A. M. Vints University Hospital of Antwerp (with permission)

**Figure 3.** Operative view: endocyst layer that gives rise to larval scolices (arrow)

#### **3.2. Cyst classification [4]**

**Figure 1.** Life cycle (dog-sheep cycle) of *E granulosus.* Diagram shows the most prevalent life cycle of *E granulosus,* in which a dog and sheep serve as the definitive and intermediate hosts, respectively. Radiographics 2000; 20:795–817

Morphologically, hydatid cyst consists of three layers and hydatid fluid. The first is the avascular outer pericystic layer or adventitia which is the host tissue formed by the lung as a reaction to the foreign body (parasite) (Fig 2). The other two layers, the laminated mem‐ brane (external layer of the cyst) or the ectocyst laminated membrane is an acellular laminar mucopolysaccaride layer and the germinative layer (inner layer of the cyst), or endocyst lay‐

The cyst fluid resembles water in appearance which may contain daughter vesicles. The cysts exist in different forms: intact or ruptured, single or multiple, unilateral or bilateral, solely located in the lung or concomitantly in other organ lodgements (especially in the

(With permission)

196 Principles and Practice of Cardiothoracic Surgery

**3. Pathology**

liver).

**3.1. Cyst structure**

er that gives rise to larval scolices (Fig 3).

Based on morphology the cyst can be classified into 4 different types:

	- **type IIa**: round daughter cysts at periphery
	- **◦ type IIb**: larger, irregularly shaped daughter cysts occupying almost the entire volume of the mother cyst

**◦ type IIc**: oval masses with scattered calcifications and occasional daughter cysts

suspected unacceptable because of the possibility Echinococcus cyst rupture, risk of falling hydatid fluid in the pleura with the development of severe anaphylactoid reactions and col‐

Thoracic Hydatid Cyst: Clinical Presentation, Radiological Features and Surgical Treatment

http://dx.doi.org/10.5772/53533

199

(a) (b)

**Figure 4.** (a) Chest radiograph demonstrates multiple peripheral round areas of soft-tissue opacity.(b) CT scan shows a clearly defined capsule with a relatively hypo attenuating center, a finding that reflects the cystic nature of the lesions.

Bronchoscopy is unnecessary in patients with a typical clinical and radiological picture but it can be performed for differential diagnosis in cases of atypical radiological appearance [5, 6]. When bronchoscopy was performed in thoracic hydatidosis, pathologic findings were re‐ vealed in 70%. Bronchoscopy detected a whitish endobronchial lesion imitating endobron‐

**Figure 5.** Flexible bronchoscopic image in a 42-year-old man with hemoptysis showing a white gelatinous membrane-

When a cyst becomes infected or ruptures, the clinical and radiological profile can mimic diseases such as nonresolving pneumonia, tuberculosis, and abscess or tumor of the lungs. Direct bronchoscopic visualization with biopsy allowed to quickly clarifying the diagnosis,

like structure protruding from the medial basal segment of the right lower lobe; CMAJ (with permission)

onization by the parasite. (Fig 4a, Fig 4 b)

chial tuberculosis with a caseous lesion. (Fig 5)

