Following perforation of the cortex and periosteum, the vesicles spill out into the adjacent soft tissues, causing a paraspinal abscess (Fig. 3.142) which must be differentiated from tuberculosis, malignancy, or mediastinal tumor (Fig. 3.143). This may in turn cause erosion of the lateral margins of the vertebral bodies, the pedicles, and posterior ribs. If the cysts break through into the neural canal, the hydatids may appear in the meninges and cause widening of the interpedicular space on the frontal view and scalloping of the posterior surface of the vertebral body on the lateral view (Fig. 3.144). In the past, myelography usually revealed a partial or complete block (compression myelopathy) at the site of the hydatid (Fig. 3.141). Today, CT and MRI, where available, have replaced, or are sometimes combined with, myelography and usually present a more complete evaluation of the true extent of the hydatid process within the spine and adjacent structures (Fig. 3.145).

The diagnosis of spinal hydatid disease is very difficult in the early stages and must be differentiated from a hemangioma or an inflammatory lesion, such as tuberculosis or brucellosis. Metastatic cancer must also be considered in the differential diagnosis, but preservation of the height of the vertebra and extension of the disease process to the adjacent posterior rib would favor hydatid disease (although tuberculosis can sometimes behave in the same way and mycotic infections will also spread to bone). When a hydatid abscess complicates hydatidosis of the dorsal spine and lies anterior or lateral to the spine, it will have to be differentiated from a pulmonary hydatid cyst or mediastinal tumor (Fig. 3.143). If CT and MRI are unavailable, a pneumothorax may be used to locate the mass more accurately. If located within the lung, it will collapse along with the lung; otherwise it will remain attached to the thoracic wall.

Fig. 3.143 Lateral tomogram of two large hydatid cysts involving the dorsal spine but presenting as mediastinal tumors. One cyst arises from the seventh thoracic vertebra, while the other overlies the anterior aspect of the mid-dorsal spine at a slightly lower level. Note the large erosive lytic defect in the anterior aspect of T7. (Courtesy of the University of Cape Town Radiology Library).

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Fig. 3.144 Scalloping of the posterior surface of a vertebral body seen on lateral view of the spine in two different patients. As the hydatids break through into the neural canal they may appear in the meninges and cause widening of the interpedicular space on frontal view and scalloping of the posterior aspect of the vertebral body on lateral view. (A) Posterior scalloping of T7 vertebra. (B) Scalloping of the posterior aspects of L2 and L3 in another patient. (Courtesy of the late Dr. Harold Jacobson, Bronx, New York).

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Fig. 3.145 Primary hydatid disease of the lumbosacral spine with destruction of the left pedicles of L3-5 and extension of a large paraspinal cystic mass into the spinal canal. A 67-year-old Saudi Arabian woman was admitted to hospital for low back discomfort of long duration. She had a normal neurological exam but had difficulty walking and no flexion contracture of the hips. A moderately firm mass was palpable in the left flank. (A and B) PA and lateral radiographs of the lumbosacral spine show partial destruction of L3-5 vertebrae and left pedicles (arrows) with a paraspinal mass (curved arrows). (C) A bone scan (99Tc-methylene diphosphonate) shows isotope uptake in the lower lumbar spine (arrows). (D-I) Nonenhanced CT scan shows a large lobulated left paraspinal cystic mass. Note the destruction of the left pedicles and extension of cysts from the vertebrae to the spinal canal. The paraspinal cystic mass contains daughter cysts. (D) L3 level. (E) Upper section L4. (F) Lower section L4. (G) L5 level. (H) Detail of bony destruction and intraspinal canal extension at L3. (I) Detail of bony destruction and intraspinal canal extension at L4. At surgery, multiloculated cysts were found in the retroperitoneal area which were of grape-like appearance and originated from the lumbar spine. Histological analysis confirmed hydatid disease. (Courtesy of Drs. von Sinner and Akhtar and Skeletal Radiology, 1994).

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