INTRODUCTION
Spondylodiscitis is defined as the infectious involvement centered on the intervertebral disc and the adjacent vertebral bodies.
In children infection often starts in the intervertebral disc itself because direct blood supply is still presente.
In adults infection begins at the vertebral body endplate,
extending into the intervertebral disc space na then into the adjacente vertebral body endplate.
It corresponds to 2 - 7 % of all osteomyelitis,
and its has a mortality rate of 2 - 12% of cases (when pyogenic).
The pyogenic spondylodiscitis spinal column involvement is more common in lumbosacral column (48%),
than thoracic (35%) and cervical (6.5%) columns.
When not pyogenic the thoracic spine is often affected,
than lumbosacral and cervical columns.
Imaging studies play a key role in the diagnosis of discitis,
but not always the imaging findings are conclusive and not infrequently there are pitfalls that hinder accurate initial diagnosis.
The early diagnosis and treatment is the key to a favorable outcome,
once an residual functional deficit occurs in up to 15% of cases.
PYOGENIC SPONDYLODISCITIS
In pyogenic spondylodiscitis Staphylococcus Aureus is the most common pathogen in immunologically normal patients and Salmonella sp. is the most common in patients with sickle cell anemia.
The pyogenic spondylodiscitis epidemiology has a bimodal distribution,
with two peaks,
one in childhood and the other in the 6th to 7th decades of life.
It is more frequent in male subjects and is related with some predisposing factors such as:
- remote infection (present in 25% of cases),
- use of intravenous drugs,
immunosuppression,
- chronic medical conditions,
The pyogenic infection spread occurs by hematogenous (major route) or contiguity of the adjacent bones in 95% of cases.
Iatrogenic and postoperative disseminations occurs in 2.5% to 5% of cases.
NON-PYOGENIC SPONDYLODISCITIS
In non-pyogenic spondylodiscitis the most common pathogens includes Mycobacterium tuberculosis,
Cryptococcus neoformans,
Candida sp.,
Brucellae sp. and Granulomatous. It is more prevalent between the 5th and 6th decades of life and in male patients.
Predisposing factors includes:
- immunosuppression,
- chronic medical conditions,
- diabetes mellitus,
- malnutrition.
The non-pyogenic infection spread also occurs by hematogenous or contiguity of the adjacent bones.
PICTORIAL ESSAY:
A) CASE 1:
Fig. 1: Case 1
*Teaching points:
- Infectious spondylodiscitis have a higher prevalence in immunosuppressed patients (treatment for rheumatoid arthritis).
- In cases of espondilodiscal involvement suggestive of Modic I,
we should pay attention to the adjacent soft tissues involvement,
as this may be the only sign of an infectious etiology.
- In the post-treatment control images of infectious spondylodiscitis there is commonly a dissociation between clinical improvement and imaging findings.
In this case,
reduced adjacent soft-tissues involvement may indicate good therapeutic evolution.
B) CASE 2:
Fig. 2: Case 2
*Teaching points:
- Although the image aspect is highly suggestive of spondylodiscitis,
it must be considered the possibility of other entities such as an acute Schmörl node.
- Thus,
the disc morphology,
particularly the identification of endplate defects or intranuclear cleft bending of the disk,
may be helpful for the correct diagnosis of acute Schmörl's nodes.
C) CASE 3:
Fig. 3: Case 3
*Teaching points:
- In cases of suspected tuberculous spondylodiscitis findings of exuberant but indolent destructive process are common,
such as: sclerotic margins,
lobulated fluid collections and calcifications among the necrotic areas in the CT scans.
- In addition,
there is often a dissociation between the degree of involvement of the vertebral bodies and adjacent soft tissues relative to the intervertebral disc,
which seems relatively spared.
- Finally,
the sharp hypointense T1 and T2 signal in the affected vertebral bodies,
even greater than that present in cases of pyogenic discitis,
may be a clue to guide the diagnosis of tuberculous or fungal etiology.
D) CASE 4:
Fig. 4: Case 4
*Teaching points:
- When facing a vertebral body with hypointense T1 signal the hypothesis of spondylodiscitis should indeed be considered in the differential diagnosis.
- However,
if this there is a sharp hypointensity on T1,
a nodular configuration or,
especially,
if there is no spondylodiscal locoregional destruction,
other hypotheses must be considered,
such as tumors.
E) CASE 5:
Fig. 5: Case 5
*Teaching points:
- The pathogens that do not produce proteolytic enzymes,
such as mycobacteria,
tend to spread and compromise the disc space more slowly. This pathogens also lead to later clinical manifestations with a cycle of destruction and repair taking several months to be completed.
- The appearance of fluid collection with sclerotic and lobulated halo,
with permeative calcifications,
is highly suggestive of tuberculous spondylodiscitis.
- Finally,
few cancers affect subsequent vertebral bodies in a continuum with the disc commitment.
An example of this manifestation occurs in lymphomas and prostate metastases.
F) CASE 6:
Fig. 6: Case 6
*Teaching points:
- Even in cases whose spectrum of imaging findings clearly suggest infectious spondylodiscitis,
clinical data should always guide the diagnosis / treatment plan.
- As exemplified by the case,
there are some rare tumors that can show indistinguishable imaging findings of an infectious spondylodiscitis with contiguous involvement of two vertebral bodies and the corresponding intervertebral disc. The lymphoma and prostate tumor metastasis are the two main tumoral causes.
G) CASE 7:
Fig. 7: Case 7
*Teaching points:
- In children under 6 years of age the infectious process begins in the intervertebral disc,
as there are still local vascularization.
Then the process extends to the adjacent vertebral bodies.
- From adolescence,
the process begins in the endplate of the vertebral plateau,
the more vascularized area at this stage,
and then extends to the disk and adjacent vertebral body.
- In infants up to 6 months old the infection is not locally restricted and quickly progresses with septicemia.
H) CASE 8:
Fig. 8: Case 8
*Teaching points:
- Differentiating between a bone infarction and an infectious spondylodiscitis is a diagnostic challenge.
Both conditions can lead to areas of edema and heterogeneous enhancement.
- The hyperintensity on T1-fat-supressed-weighted images without contrast represent areas of medullary infarction,
with dense red blood cells sequestered in the bone marrow and subperiosteal spaces.
These areas also have hyperintense signal in T2,
but the enhancement is only peripheric.
- The soft tissue involvement may favor the diagnosis of infectious spondylodiscitis.
I) CASE 9:
Fig. 9: Case 9
*Teaching points:
- In patients with chronic renal disease the finding of exuberant destructive involvement of the vertebral bodies can easily be misinterpreted as a spondylodiscitis.
- A valuable tip to help in the differential diagnosis of a spondylopathy of patients with chronic kidney disease is the relative preservation of facet joint.
- Another finding that favors the diagnosis of spondylopathy of patients with chronic kidney disease is the intradiscal gas finding.
J) CASE 10:
Fig. 10: Case 10
*Teaching points:
- Just like the case of spondylopathy in patient with chronic kidney disease in patients with spinal neuroarthropathy the differential diagnosis of espondilodiscal involvement in relation to an infectious spondylodiscitis can be very difficult.
- In spinal neuroarthropathy the dissociation between the involvement of the vertebral bodies / discs and facet joint should also be used as a hint to guide the differential diagnosis,
as well as in spondylopathy of patients with chronic kidney disease,
the interapophyseal joints are also spared.
- In addition,
the finding of intradiscal gas and reactive sclerosis in the tomographic studies or magnetic resonance imaging also favor the hypothesis of spinal neuroarthropathy.
L) CASE 11:
Fig. 11: Case 11
*Teaching points:
- In the post-junctional arthrodesis syndrome the level immediately above the arthrodesis ends up receiving an axial overload which can trigger the cascade of spondylodiscal degenerative changes.
- The spectrum of findings may sometimes overlap to a infectious spondylodiscitis.
For accurate differential diagnosis attention should be paid to the involvement of paraspinal soft tissue,
much more exuberant than in purely degenerative contexts non-inflammatory / infectious.
- In the exemplified case the retrovertebral fluid collection appeared as confounder,
but after characterized as a hematoma,
the diagnosis of spondylodiscitis lost power at the expense of a junctional post-fusion syndrome.