CT of pelvis
A 54-year-old female patient presented with low back pain.
Craniotomy 10 years ago and under medical treatment since. Sacral operation 3 years ago, followed by debridement of the wound.
X-ray and CT of pelvis demonstrates several lytic, expansile lesions of sacrum and right hemipelvis fistulation of right iliac wing lesion to the skin, soft tissue masses of retroperitoneum, right psoas muscle, right inguinal region, abdominal wall, and bilateral gluteal muscles (Figure 1-2).
MRI of upper abdomen reveals the primary site of infestation in liver showing a hypointense collapsed rim of the calcified eccinococcus alveolaris, also evident on chest x-ray (Figure 3-4).
MRI shows multiple, multicystic right paravertebral soft tissue masses by the psoas muscle and bony lesions of sacrum and right ilium with no contrast enhancement (Figure 5-6).
Destructive expansile lesion of sacrum extending towards presacral space as well as the spinal canal is detected with MRI of lumbosacral vertebrae. There is no significant enhancement within the lesion, however, peripheral contrast uptake is seen (Figure 7).
Hydatid disease is a parasitic zoonosis caused by the Echinococcus tapeworm. Alveolar echinococcosis (AE) is a rare, aggressive, debilitating type caused by Echinococcosis multilocularis. Lifelong treatment is needed for disseminated disease (1-4).
The diagnosis was established by histopathology and serology 10 years ago. Liver, intraabdominal, soft tissue and bone lesions were followed-up with imaging. They were stabile under albendazole treatment since.
Early detection with complete surgical resection is the only curative treatment. Lifelong benzimidazole therapy is an effective option for chronic unresectable cases.
AE mimics slow-growing tumours both in liver and other organ systems. In contrast to the common form E. granulosis, EA does not form a well-defined, encapsulated mass, but tends to infiltrate the neighbouring structures.
AE infestations are initially localized to liver and may spread directly to adjacent organs. Larvae may also disseminate via lymphatic ducts and blood vessels most commonly to the lungs and brain. Morphologic and thus imaging characteristics of EA in other organ systems are similar to primary liver lesions. Cystic necrotic features are better shown by US and MRI. ‘Hailstorm pattern’ seen as multiple clustered hyperechoic nodules, mimicking hemangiomas in liver lesions, is a less common presentation (1). There is no significant enhancement within the lesions, however, peripheral enhancement may be detected on late venous phase. Lack of restriction on diffusion-weighted images is useful in differential diagnosis with malignant lesions (1).
The World Health Organization Working Group on Echinococcosis established the ‘PNM’ classification system (P: Hepatic parasitic mass, N: Involvement of neighbouring organs, M: Involvement of distant sites) in order to standardize evaluation of resectability and improve outcomes (5-8).
Osseous dissemination is exceedingly rare and seen in about 1% of cases (9-11). Most common sites are sternum and vertebrae. Lytic bone lesions which may be complicated by pathological fractures, have an invasive and destructive character, mimicking metastases, tuberculosis and Paget’s disease.
Soft tissue lesions appear as clusters of small cysts with thick septa. Tuberculosis is an important differential diagnosis in cases with a psoas abscess.
Prognosis is generally poor and lifelong treatment may be needed. It is fatal if left untreated, with death resulting from complications related to liver, heart, lung or brain involvement.
Take-Home Message, Teaching Points
Characteristic imaging findings of AE put the radiologists at a pivotal role in suggesting the diagnosis, especially in endemic regions. The disease is slowly progressive with tumour-like growths in liver and dissemination sites.
Written informed patient consent for publication has been obtained.
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