All hydatid lesions start as purely cystic type I structures (Fig. 3.22), and if they develop daughter cysts or matrix (or both) they are termed type II cysts (Fig. 3.23). When the only remaining hydatid fluid is in daughter cysts, the lesion can be considered hypermature as it is probably nearing death by starvation (Figs. 3.23 & 3.24). When formed elements completely replace the nourishing hydatid fluid, the type II lesion is starved, dies, and eventually becomes an end-stage calcified and biologically inert type III lesion (Fig. 3.25).

Fig. 3.22 Transverse CT scan through the liver showing type I hydatid cysts. Hydatid sand, composed of brood capsules and scolices, settles to the dependent portion of the cyst but it cannot be resolved on CT images. However, sand can be shown by ultrasound if the patient is rotated immediately before scanning so that the settling particles resemble a snow storm. An uncalcified pericyst and intact endocyst in intimate contact with the pericyst are not visible, but after rupture, a detached endocyst becomes visible by ultrasound, CT and MRI. Note dilated pericystic ducts (arrows). (Courtesy of Dr. Lewall and Clinical Radiology, 1998).

Fig. 3.23 Transverse ultrasound scan of a liver hydatid showing pseudotumoral appearance due to the abundance of echogenic matrix. The margins of the hydatid were defined by the sonographer with crosses. The fluid-containing daughter cysts (arrows) indicate the true nature of this hypermature type II cyst. (Courtesy of Dr. Lewall and Clinical Radiology, 1998).

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Fig. 3.24 (A) Transverse CT scan through liver and spleen showing hypermature type II hydatids in both organs with multiple daughter cysts and considerable matrix. Note dilated bile ducts anterior to the liver cyst. (B) Type II hydatid cyst in a cut spleen from another Saudi Arabian. Daughter cysts, which are embedded in matrix, originally completely filled the impressions in the matrix; the gaps between the two are artefactual due to dehydration of the daughters during formalin fixation. This is a hypermature lesion which probably would not have ruptured. (C) Photomicrograph of matrix (same patient). Note the folds of laminated membrane (long arrows), vestiges of scolices (large arrowheads) and hooklets (small arrowhead), all in advanced stages of degeneration. (H&E; X 250). (Courtesy of Dr. Lewall and Clinical Radiology, 1998).

Fig. 3.25 Heavily calcified endocyst and pericyst of a biologically inert type III pelvic hydatid.