Prepared by
Allen J. Levy, MD,
Department of Radiology and Nuclear Medicine, Brooke Army Medical
Center, Ft. Sam Houston, TX;
Peter B. Wold, MD,
Department of Radiology, The Mayo Clinic, Rochester, MN;
Douglas P. Beall, MD,
Assistant Professor of Radiology, Department of Radiology and
Nuclear Medicine, The Uniformed Services Health Sciences
University, San Antonio, TX; and
Justin Q. Ly, MD,
Department of Radiology and Nuclear Medicine, Wilford Hall
Medical Center, Lackland AFB, TX.
CASE SUMMARY
A 42-year-old man from the Middle East presented with 3 months
of dull, progressive back pain. Approximately 6 weeks previously,
he had developed a right L5 radiculopathy, pain in the lateral
right thigh, and numbness of the right great toe. Radiographs
obtained at the time of presentation were interpreted as consistent
with metastases to the axial spine. The patient had no known
primary malignancy. The physical examination revealed weakness of
the left extensor hallucis longus, palpable tenderness over the
L3-L4 spine, and significant pain during flexion of the lumbar
spine.
DIAGNOSIS
Tuberculous (TB) spondylitis without discitis. Mycobacterium
tuberculosis detected by polymerase chain reaction (PCR) from
computed tomography (CT)-guided biopsy of left psoas muscle
mass.
IMAGING FINDINGS
The skeletal survey revealed lytic lesions at the medial aspect
of the right 1st rib, spinous process of L3, and involving the
entire T11 vertebral body (Figure 1). A paraspinal mass is seen at
T11 on the right, and there is a prominent left hilum.
Contrast-enhanced CT of the chest, abdomen, and pelvis (Figure
2) showed multiple indeterminate, low-attenuation, lytic lesions in
the cervical, thoracic, and lumbosacral spine, right ilium, and
right 1st and left 10th ribs. Soft-tissue extension across the
vertebral cortex was observed with several lesions. Moreover, there
was low-attenuating soft tissue extending from the L4 vertebral
body anterolaterally into the left psoas muscle. Additional
findings included an infiltrate involving the superior segment of
the left lower lobe and left hilar enlargement.
Magnetic resonance imaging (MRI) of the lumbar spine revealed
multiple lesions with low T1 and high T2 signal in the lower
thoracic and lumbosacral spine and right ilium (Figure 3). A lesion
at L5 protrudes into the ventral epidural space. There is
soft-tissue extension into the paraspinal muscles at T11-12, L4,
and L5. A prominent L3 spinous process lesion extends into the
adjacent soft tissue.
DISCUSSION
The characteristics of spinal TB have changed over the last 20
years. The prevalence of TB has remained high in the developing
world and the proportion of TB cases occurring in foreign-born
patients is increasing in industrialized nations. In some studies,
up to 70% of patients with skeletal TB are foreign-born.
Diagnostic techniques, such as CT, MRI, and percutaneous
image-guided biopsy, have facilitated early diagnosis of spinal TB.
Other differential considerations include pyogenic spondylitis,
lymphoma, sarcoidosis, brucellosis, myeloma, and metastasis.
Francis et al
1
reported positive acid-fast bacilli cultures in 82.9% of spinal TB
cases using image-guided fine-needle aspiration and/or needle
biopsy. In addition, the imaging techniques have enabled physicians
to confirm an atypical pattern of spinal TB that spares the disk
space.
2-7
Two distinct patterns of spinal TB have been identified; the
classic form is known as tuberculous spondylodiscitis (SPD). The
second form, tuberculous spondylitis without discitis (SPwD), is
becoming increasingly more common.
2
Tuberculous spondylitis accounts for 50% to 60% of skeletal TB,
which itself accounts for 5% of all cases of TB.
2,3,7,8
The L1 vertebral body is affected most commonly and the frequency
of involvement decreases in either direction from this level.
2,3
Usually, more than one segment is involved and up to 5 to 10
segments are not uncom-monly seen.
2,3,6,7
The infectious process is believed to begin as a single focus in
>95% of cases. Arterial hematogenous spread is the most likely
means of spread.
2,4,5
In most cases, spinal TB begins as an infectious focus in the
anterior aspect of the vertebral body adjacent to the subchondral
bone plate. Spread to the disk is common and may occur via direct
extension through the subchondral bone plate or under the anterior
or posterior longitudinal ligament.
2,3
This becomes radiographically apparent in 2 to 5 months as a
destructive lesion with little or no surrounding sclerosis and loss
of disc height. Subligamentous extension into additional vertebral
bodies can occur, easily leading to multilevel involvement.
5
The combination of vertebral body and disc destruction is similar
to that seen with pyogenic discitis, but distinctly different are
the indolent course and multilevel involve-ment of spinal TB.
3,7
Extension into the paraspinal ligaments and soft tissues is
common and usually occurs anterolaterally.
6
Once established in the paraspinal soft tissues, it may remain
localized or extend for a considerable distance.
3,7
Burrowing abscesses can extend for incredibly long distances before
penetrating an internal viscus or the external body wall. Abscess
formation is usually bilateral and fusiform.
3,5,8
Tuberculous psoas abscesses may contain calcification,
8
whereas pyogenic abscesses rarely calcify. The calcifications may
be either amorphous or tear-drop shaped and occur between L1 and
L5.
8
CT and MR imaging signs of psoas abscess are nonspecific and can be
found in hematoma and tumors, although calcification is more common
in TB.
2,6
Occasionally, the posterior elements are the initial site of
involvement. Radiographic findings include spinous process,
pedicle, or laminal destruction. Paraplegia can occur. The
differential diagnosis includes other infections and neoplastic
processes.
2,5
Collapse of a partially destroyed vertebral body can lead to
severe short segment kyphosis or gibbus deformity.
3,7
Occasionally, conventional radiography will reveal long lumbar
vertebral bodies if the deformity occurred before skeletal
maturity.
Pertuiset et al
2
described SPwD as an atypical form of spinal TB found predominately
in young, foreign-born patients. The distinguishing feature of TB
SPwD is the absence of disc destruction. Patients with SPwD were,
on average, 10 years younger (39.8 years) than those with classic
SPD and were much more likely to be foreign born (mostly from
sub-Saharan Africa). Approximately 95% of the Pertuiset's classic
tuberculous SPD group had a single initial focus of involvement in
keeping with previous descriptions of SPD. However, the SPwD group
had a 42% rate of initial multifocal vertebral body involvement.
Moreover, the SPwD group was 9 times more likely to have
extraspinal skeletal involvement.
2
CONCLUSION
There are two distinct patterns of spinal tuberculosis:
tuberculous spondylodiscitis, and, an increasingly common atypical
form, tuberculous spondylitis without discitis. The treatment is
the same for both entities. Without disc destruction, fine-needle
aspiration or biopsy is needed to differentiate SPwD from
metastasis or myeloma in nearly all cases. Polymerase chain
reaction, which can rapidly identify
Mycobacterium tuberculosis
even in the presence of a negative acid-fast bacillus stain, should
significantly increase the sensitivity of fine-needle aspiration or
biopsy.
2