Unusual MR presentations of Pyogenic Spondylodiscitis

Unusual MR presentations of Pyogenic Spondylodiscitis –

H.S.Das N. Medhi, P.Sarma, P.Goswami, , P.Hazarika.

Infective (Pyogenic and tubercular) spondylitis is a relatively common entity in day-to-day practice. Though commonest cause of such infection is tuberculosis in our country, pyogenic infection of the spine is also frequently encountered. Majority of these pyogenic infections of the spine are iatrogenic in nature, though in some cases the cause and source of infection cannot be ascertained. We report 4 patients of infective spondylodiscitis with unusual presentations.

Case-1: 43 yrs female patient had laparoscopic cholecystectomy in a local hospital. She was nondiabetic and nonhypertensive and blood examination revealed mild anemia and slight rise in the TSH. After surgery was uneventful and she was kept in the intensive care unit overnight and sent to the paying ward after 24 yrs. Her immediate postoperative status was perfectly all right. On 2nd postoperative night she developed excruciating pain and she got partial relief of pain after putting her on continuous parenteral analgesics. Though her pain remained unaltered she was discharged on the 4th day only with analgesics. As pain did not subside an MR examination of the cervical spine was performed. MRI showed significant loss of cervical lordosis with hazy epidural space and provisionally the treatment was continued as cervical sprain. She continued to have pain and later on she developed difficulty in lifting the head. Second MR was performed on 3rd week due to detorioration of her condition and showed evidence of spondylodiscitis at C5-C6 level. She was provisionally put on antibiotics (amikacin 500 mg iv x2weeks followed orally for 6weeks).

Case no 2. 35 yrs old patient had tonsillectomy for chronic tonsillitis. The surgery was carried under general anaesthesia and it was uneventful as far as the primary disease is concerned. He was non-diabetic and nonhypertensive. On third postoperative day the patient developed severe pain in the neck with out significant radicular pain. He was discharged from the hospital with simple analgesic without significant improvement in the condition of the neck pain. As patient deteriorates further an MR examination was performed. MR study reveals involvement of the C5-C6 disc by T2 hyperintense collection, marrow edema involving C5 and C6 vertebral bodies, prevertebral and epidural soft tissue collection. Due to significant compression of the cord surgery was performed to relive the compression and to get a histological diagnosis. At surgery the involved bones were very soft and infected material was removed from the site. Bacteriological and histological diagnosis was pyogenic infection and culture shows growth of pseudomonas infection. The organisms were sensitive to amikacin and gentamycin. Patient improved after surgery.

Case. No 3: 28 yrs female patient had CS under GA. The patient was not diabetic and nonhypertensive. Her pre operative blood and other laboratory parameters were grossly normal. The patient developed severe pain in the neck on 3rd postoperative day. She was also managed by rest and analgesics thinking it to be cervical spondylosis. As her status remains same in spite of rest and analgesics she was investigated by cervical MR. The MR showed features of spondylodiscitis at C5-C6 level with significant thecal compression by the epidural soft tissue component. There was prevertebral abscess also. As her condition continues to deteriorates decompressive surgery was performed. At surgery thick pus with granulation tissue was removed and sent for biopsy and bacteriological study. At pathology features were suggestive of pyogenic spondylodiscitis with salmonella infection. The organisms were sensitive to ciprofloxacin group of antibiotics and not very sensitive to the amikacin and gentamycin. She was put on parenteral antibiotics for 2weeks followed by oral antibiotics for 6weeks. She was completely free from all symptoms.

Case 4: 30 yrs female patient had undergone CS operation. She developed severe pain in the neck on third day of her surgery. Though she was treated with neck exercise and analgesic she continued to deteroriorate and an MR examination was called for. MR study of the cervical spine reveals evidence of spondylodiscitis at C5-C6 vertebral body with epidural and prevertebral collection with mild cord impingement. She was treated was lost to follow up.

Important observations:

– All the patients were operated in the same hospital.

– All 4 patients were operated within the month of June and July. No such patients were reported before or after this period.

– The surgeons were different in all of the cases.

– All patients had involvement of the C5-C6 levels.

– Clinical presentation and course of the disease were almost similar.

Discussion:

Spondylitis is a condition where there is primary infection of the vertebral body. Disc space involvement is called discitis. Pure vertebral osteomyelitis or discitis is infrequent and most of the time there is involvement of both vertebrae and disc hence term spondylodiscitis is preferred. The third element of the spinal infection is the epidural abscess, which is also frequently associated with spondylodiscitis.

Types of spondylodiscitis: According to the offending organism the spondylodiscitis may be pyogenic or Tubercular, though rarely other organisms like Brucella, Fungal or parasites may cause spondylodiscitis.

Pyogenic spondylodiscitis
Pyogenic infection of the spine can occur by three routes- hematogenous spread, direct inoculation and contiguous spread.

Though apparent source of infection in a patient with spondylodiscitis can not be traced even after through check up in most of the patients, the common source of hematogenous spread is from infections of the urinary tract, lungs, pelvis and skin. IV injections may be the source of infection in some patients developing spondylodiscitis after surgery. In diabetics and immuno-compromised patients, a spinal infection is relatively more frequent. The disc is directly infected in children in hematogenous route due to persistence of peridiscal blood vessels. But in adult the disc is avascular and is secondarily affected.

Pyogenic spondylodiscitis can occur by direct inoculation of the disc or contiguous spread of infection. A major proportion of this type of infection is iatrogenic. Iatrogenic disc space infection is most commonly encountered following spinal surgery. This is true in our experience also, where majority of pyogenic spondylodiscitis is due to lumbar disc surgery. This is due to various factors -firstly the lumbar disc surgeries are relatively common; secondly UTI and other pelvic infections frequently involve the lumbar spine. Majority of pyogenic infections are due to staphylococcus aureus and enterobacter group. Other organisms causing pyogenic spondylodiscitis are salmonella and serratia etc.

MR findings- MRI is the single most valuable imaging technique in evaluation of pyogenic spondylodiscitis. MRI can pick up the changes at the earliest stage so that these patients can be treated soon and hence the morbidity is significantly reduced. Involved vertebral bodies reveal increased signal intensity on T2 weighted images and reduced signal intensity on T1 weighted images due to marrow edema. The intervertebral disc reveal reduced signal intensity on T1 weighted images and strong / very strong signal intensity on T2 weighted images sometimes called “hot disc”. There is irregularity in the vertebral end plates with destruction sometimes.
In more advanced cases there is progressive destruction of the vertebral bodies. There is prevertebral soft tissue and epidural lesions in advanced cases.

Tubercular Spondylodiscitis: TB spondylodiscitis most commonly occurs by hematogenous route and generally affects all age groups. The vertebral body is primarily involved with secondary involvement of the appendages, disc and epidural space. There may be involvement of the cord also producing intra-medullary tuberculoma. Lower thoracic and upper lumbar vertebrae are more commonly affected.

MRI findings MR usually pick up the findings very early. There is involvement of two contiguous vertebral bodies including the disc. Involvement of more than two vertebral bodies and areas of skip lesions are frequently encountered. The involved vertebral bodies reveal reduced signal intensity on T1 weighted images and appear iso to hyperintense on T1 weighted images. There is involvement of the posterior elements and lot of epidural granulation tissue or frank collection is seen. Arachnoiditis and intra-medullary tuberculomas may be found.

click to see picture: tb-spine-photo

MR findings of TB Vs Pyogenic spondylodiscitis

Disc space involvement is common in pyogenic infection. The disc becomes hyperintense on T2 weighted images classically described as “hot disc”.
In tubercular infection the posterior elements are also involved which is uncommon in hematogenous pyogenic infection.
More than two vertebral body segments are frequent in TB and there are skip lesions in some cases.
Epidural space, spinal meninges and cord involvement more frequent in TB than pyogenic infection.

Other infections:

Other uncommon causes of spondylodiscitis are Brucella, fungal and rarely parasitic. Brucella spondylitis is characterized by erosion of the anterior aspect of the superior end plate. There is significant sclerosis along with lytic lesions. In fungal spondylitis the responsible organisms are blastomycosis, cryptococcosis and coccidiomycosis. There are destructive lesions, paravertebral soft tissue mass, multiple sites of involvement and relative sparing of the disc are some of the features of fungal spondylodiscitis.

Conclusion: MRI plays a vital role in diagnosis and management of spondylodiscitis. It has highest sensitivity in diagnosis such cases, where it can characterize most of these patients. Unusual presentation of infective spondylitis may cause confusion in diagnosis; FNAC or biopsy may be necessary in some of these patients. Difficulties may arise in differentiating spondylodiscitis with type-1 end plate change, where contrast study may be helpful. Similar problems may arise in cases where infection co-exists in pre existing tumor, where biopsy will give the final diagnosis.