Spleen

Hydatid cysts within the spleen behave in the same way as hydatids in the liver. They may be primary or secondary, solitary or multiple. Primary hydatids develop from larvae reaching the spleen via the arterial circulation. The first clinical indication of the presence of a splenic hydatid cyst is usually splenomegaly. If no typical calcification is present, an uncomplicated cyst may not be recognized. Single hydatid cysts may grow to a considerable size, almost totally replacing the splenic parenchyma. Multiple hydatid cysts of different sizes may also occur. Secondary hydatids of the spleen may result from extension of a peritoneal hydatid or metastases from other sites.

Clinically there may be pain or discomfort in the left upper quadrant and a palpable mass. Most cysts are painless, but when there is pain it usually results from communicating or direct rupture. Occasionally a cyst arising from the lower pole of the spleen may rupture into the peritoneum, leading to secondary peritoneal hydatids and sometimes causing an abdominal emergency. A splenic cyst can rupture also into the stomach, colon, or rarely the left kidney. Cysts arising from the upper pole of the spleen may rupture through the diaphragm into the pleura or lung (Fig. 3.68), causing secondary pleural or pulmonary hydatidosis. Such direct rupture may occur when there are adhesions between the pericyst and adjacent organ.

Fig. 3.68 Hydatid cyst of the spleen. (A) Noncontrast CT scan shows a ruptured hydatid cyst (arrows) prolapsed into the left lower hemithorax. (B) MRI, coronal plane, of same patient. A splenic hydatid has prolapsed into the left hemithorax. Level of left hemidiaphragm (black arrows). Hydatid pericyst of low signal intensity (white arrows) is noted with surrounding pulmonary parenchymal reaction. (Courtesy of Dr. von Sinner and Acta Radiologica, 1992).