The liver is the most common location of hydatid cyst (Jerraya et al. 2015). During the evolution of the liver hydatid cyst, endogenous and exogenous formations called daughter cysts may appear (Lee et al. 2000). Daughter cyst sign is one of the most characteristic imaging findings of liver hydatid cysts. It is essentially reported in CE 2 and 3 of WHO-IWGE ultrasound images classifications (Group WIW 2003). It is schematically divided into two types according to the daughter cyst localization in regard to the hydatid cyst wall. The first represents a small cyst that protrudes into the lumen of the cystic mass and the second lies along the outer wall of the cyst (Lee et al. 2000). The exogenous daughter cysts are enclosed in the laminated layer then gradually pushed outwards (Fig. 1a), giving the hydatid a bumpy appearance that distorts the classic circular radiological image (Klotz et al. 2000). Endogenous daughter cysts are not enclosed in the laminated layer, they float in the mother cyst and have a reproductive role (Fig. 1b). Daughter cysts can be easily identified with an abdominal ultrasound. It reveals a hypoechoic to anechoic cysts in the lumen of the mother cysts or enclosed in the mother cyst wall (Fig. 1a) (Klotz et al. 2000). In CT-scan, it is seen as peripherally arranged cystic lesions appearing in the lumen of mother cyst with high-attenuation oval or round masses (Klotz et al. 2000). Concerning MRI findings, the presence of daughter cysts is seen as endogenous or exogenous proliferations more or less joined to the germinative layer, with a hypointense signal compared to that of the intracystic fluid with T1 weighting and spin-density weighting. On T2-weighted images, the signal intensity of the daughter cysts was higher and was confused with that of the hydatid matrix (Marani et al. 1990; Pendse et al. 2015). Surgery is the treatment of choice of liver hydatid cyst. It can be conservative or radical. It is associated with a recurrence rate of 10% (Jerraya et al. 2015). It can be due to various mechanisms like dissemination during the surgical procedure of an endogenous daughter cyst (Fig. 2) or to missed exogenous daughter cysts after conservative surgery (Jerraya et al. 2015). It is widely admitted that exogenous daughter cysts are more determinant than endogenous daughter cysts in recurrence rate. These exogenous daughter cysts were identified in 16% to 19% of hydatid cyst cases (Voros et al. 1999; Tagliacozzo et al. 2011). These rates were similar to the average rates of hydatid cyst recurrence reported in the literature after conservative surgery (Tagliacozzo et al. 2011; Yorganci and Sayek 2002). Imaging findings were relevant to detect these daughter cysts and dictate some additional precautions during surgical procedures. They guide surgeons to remove them, especially, in case of conservative treatment. If we detect many exogenous daughter cysts, a radical treatment should be favored otherwise the post-operative recurrence will be certain. Moreover, surgery of a secondary recurrence of liver hydatid cyst is technically more difficult with considerably increases of mortality and morbidity rates of this benign pathology.

Fig. 1
figure 1

Axial abdominal CT scan image (a): exogenous daughter cyst appearing as a peripherally lined round lesion with fluid in the center with higher attenuation values than the mother cyst (red arrow) representing the daughter cyst sign of an exogenous daughter cyst. Endogenous daughter cyst appearing in the lumen of mother cyst with high-attenuation oval masses (white arrow) representing the daughter cyst of an endogenous daughter cyst. Liver ultrasound image (b) objectifying many hypoechoic round cystic lesions occupying the periphery of a liver hydatid cyst (red arrows) representing the daughter cyst sign of an exogenous daughter cyst (color figure online)

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Fig. 2
figure 2

Intraoperative view of an endogenous daughter cyst (white arrow) localized in the lumen of mother hydatid cyst wall (white arrow)

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