Role of MRI in the diagnosis of tuberculous spondylitis (Pott's disease) Submitted by: Narzullayev E Submitted to: Dautov T. B.

Introduction Although the first documented spinal tuberculosis (TB) cases date back to 5,000-year-old Egyptian mummies, the first modern case of spinal TB was described in 1779 by Percival Pott. Tuberculosis of the spine in an Egyptian mummy

In 1779, Percivall Pott, for whom the disease is named, presented the classic description of spinal tuberculosis.

Epidemiology Bone and soft-tissue tuberculosis accounts for approximately 10-15% of extrapulmonary tuberculosis cases and between 1% and 2% of total cases. Tuberculous spondylitis is the most common manifestation of musculoskeletal tuberculosis, accounting for approximately 40-50% of cases.

Morbidity Pott disease is the most dangerous form of musculoskeletal tuberculosis because it can cause bone destruction, deformity, and paraplegia. Pott disease most commonly involves the thoracic and lumbosacral spine. However, published series have shown some variation. The lower thoracic vertebrae make up the most common area of involvement (40- 50%), followed closely by the lumbar spine (35-45%). In other series, proportions are similar but favor lumbar spine involvement. Approximately 10% of Pott disease cases involve the cervical spine.

A typical tuberculous spondylitis T2-weighted-fat- suppression MR image shows high signal intensity at the 11 th and 12 th thoracic spine and the 2 nd and 3 rd lumbar spine. And there are epidural abscess at the thoracic spine and subligamentous abscess extension at the lumbar spine

Clinical presentation Patients usually present with back pain, lower limb weakness/paraplegia, and kyphotic deformity. Constitutional symptoms (fever and weight loss) are also common.

Pathophysiology Pott disease is usually secondary to an extraspinal source of infection. Pott disease manifests as a combination of osteomyelitis and arthritis that usually involves more than 1 vertebra. The anterior aspect of the vertebral body adjacent to the subchondral plate is usually affected. Tuberculosis may spread from that area to adjacent intervertebral disks. In adults, disk disease is secondary to the spread of infection from the vertebral body. In children, the disk, because it is vascularized, can be the primary site.

Collapse and kyphosis Progressive bone destruction leads to vertebral collapse and kyphosis. The spinal canal can be narrowed by abscesses, granulation tissue, or direct dural invasion, leading to spinal cord compression and neurologic deficits. The kyphotic deformity is caused by collapse in the anterior spine. Lesions in the thoracic spine are more likely to lead to kyphosis than those in the lumbar spine. A cold abscess can occur if the infection extends to adjacent ligaments and soft tissues. Abscesses in the lumbar region may descend down the sheath of the psoas to the femoral trigone region and eventually erode into the skin.

Pathology The spine is involved due an hematogenous spread via the venous plexus of Batson. There is usually a slow collapse of one or usually more vertebral bodies, which spreads underneath the longitudinal ligaments. This results in an acute kyphotic or "gibbus" deformity. This angulation, coupled with epidural granulation tissue and bony fragments, can lead to cord compression. Unlike pyogenic infections, the discs can be preserved. In late-stage spinal TB, large paraspinal abscesses without severe pain or frank pus are common, leading to the expression "cold abscess".

Classification of Spinal TB In 2001, Mehta and Bhojraj introduced a new classification system for spinal TB using MRI findings. They classified patients to 4 groups according to the employed surgical technique. Group A Group B Group C Group D

Group A consisted of patients with stable anterior lesions and no kyphotic deformity, who were managed with anterior debridement and strut grafting.

Group B consisted of patients with global lesions, kyphosis and instability, and were managed with posterior instrumentation using a closed-loop rectangle with sublaminar wires plus anterior strut grafting.

Group C patients had anterior or global lesions along with a high operative risk for transthoracic surgery due to medical comorbidities and probable anesthetic complications. Therefore, these patients underwent posterior decompression with the anterior aspect of the cord being approached through a transpedicular route and posterior instrumentation performed using a closed- loop rectangle held by sublaminar wire.

Finally, group D patients had isolated posterior lesions that needed only a posterior decompression. This classification only categorizes thoracic lesions which is the most important limitation of this system.

MRI Among the various types of imaging modalities, MRI has the ability to diagnose the disease earlier and more accurately than plain radiographs. Although not specific to spinal TB, there is a decrease in signal intensity of the involved bone and soft tissues on T2-weighted images and the increase in intensity of a uniform thin rim enhancement is a pathogenomic finding suggesting either caseation necrosis or a cold abscess in tuberculosis. In the evaluation of spinal TB with isolated involvement of the posterior elements, MRI is also useful in diagnosis and assessment of the treatment response.

MRI Features include irregularity of both the endplate and anterior aspect of the vertebral bodies, with bone marrow oedema and enhancement seen on MRI: T1: hypointense marrow in adjacent vertebrae T2: hyperintense marrow, disc, soft tissue infection T1 C+ (Gd): marrow, subligamentous, discal, dural enhancement The paraspinal collections are typically well circumscribed, with fluid centers and well-defined enhancing margins.

Tuberculous spondylitis with large prevertebral abscess 29 year old male migrant to Australia from India who presented to Emergency with Horner's Syndrome. On examination he was found to have large swelling in the neck.

50 years old referred for evaluation of chronic back pain. destruction of bodies of L4,L5 vertebrae.There was also soft tissue mass extending into the spinal canal and tracking along paraspinal mass

Thoracic spine MRI demonstrates a kyphotic deformity involving the thoraco-lumbar region secondary to the destructive process involving the T11-12 junction. The process appears to involve the inferior aspect of the T11 and superior aspect of T12 vertebra with loss of height and evidence of paraspinal and spinal canal extension.

There was subtotal destruction of C2 and C6 vertebral bodies with less affection of C5 and extensive marrow edema and enhancement involving the cervical vertebrae down to D2. Nevertheless, there was two large paravertebral abscesses one opposite the right side of C2 with small epidural component and a larger multiloculated pre and para vertebral abscess more to the right side with epidural extension through right C6-C7 neural foramen and moreover there is an inferior extension reaching the posterior mediastinum. The two abscesses appeared connected. There was gibbus deformity at C6-C7 level.

L2/3 discitis with localised prevertebral, psoas and anterior epidural involvement. Destruction of the L3 superior endplate, with L3 vertebral body height now approximately 50% of normal. Abnormal enhancing prevertebral soft tissue at the level of the L2/3 and also abnormal epidural soft tissue at L2/3 which compresses the thecal sac and cauda equina. The urinary bladder is distended.

A large multilocular and septated fusiform para-spinal cystic collection is seen extending from T2 to T10 vertebral bodies, it shows low T1 and high T2 and STIR signal intensity. The lesion measures roughly about 16 x 6 x 5 m in its main CC and axial diameters. The lesion causes vertebral erosions and anterior vertebral scalloping. Associated vertebral osteomyelitis is seen with extensive areas of marrow oedema signal displaying low T1 and high T2 signal of the bony spine. A small posterior intra-spinal epidural cystic lesion about 6 x 0.5 x 0.5 cm is seen indenting the cord posteriorly. The dorsal discs are relatively spared with mild anterior T4/T5 spondylodiscitis. No posterior disc lesion. Normal size and signal intensity of the cord. Exaggerated dorsal kyphosis.

Marked reduction in the anterior heights of T8 and T9 vertebral bodies showing abnormal outline, irregular opposing end plates and near total obliteration of the intervening disc space. They show diffusely low T1 and bright T2 and STIR signal with contrast uptake in the post-contrast series. They are also surrounded by an irregular para-spinal and intraspinal soft tissue component that exhibits heterogeneous low T1 and bright T2 signal intensity with heterogeneous contrast uptake in the post-contrast series where it also shows areas of ring enhancement. The intraspinal component is seen effacing the ventral subarachnoid space and indenting the dorsal cord at T8-9 level. The opposing spinal cord shows bright T2 and STIR signal within.

A large multilocular and septated fusiform para-spinal cystic collection is seen extending from T2 to T10 vertebral bodies, it shows low T1 and high T2 and STIR signal intensity. The lesion measures roughly about 16 x 6 x 5 m in its main CC and axial diameters. The lesion causes vertebral erosions and anterior vertebral scalloping. Associated vertebral osteomyelitis is seen with extensive areas of marrow oedema signal displaying low T1 and high T2 signal of the bony spine. A small posterior intra-spinal epidural cystic lesion about 6 x 0.5 x 0.5 cm is seen indenting the cord posteriorly. The dorsal discs are relatively spared with mild anterior T4/T5 spondylodiscitis. No posterior disc lesion. Normal size and signal intensity of the cord. Exaggerated dorsal kyphosis.

Differential diagnosis In many parts of the developing world, TB is the most common cause of vertebral body infection, with the majority of cases seen in patients under the age of 20. TB can also affect the meninges of the spine, causing an intense pachymeningitis that enhances dramatically. brucellosis: can present as granulomatous osteomyelitis of the spine that can be difficult to distinguish from TB. Both are acid-fast bacilli, which may cause caseating granuloma(s) brucellosis fungal infection sarcoidosis pyogenic infection – insidious onset metastasis

Prognosis and Outcome of spinal TB Effective medical and surgical management of spinal TB has improved outcome of these patients significantly even in the presence of neurologic deficits and spinal deformities. However, since various surgical techniques have been used for the management of spinal TB, reported outcomes are heterogeneous and decision making for the selection of a specific technique in the management of all patients is difficult. Neurologic complications due to Pott's disease seem to be "relatively benign" if early adequate medical and surgical managements are employed. Younger age and radical surgery in conjunction with antituberculosis chemotherapy have been suggested as favorable prognostic factors. Some of the other more important factors associated with prognosis and the development of deformity during the course of spinal TB have been pointed out in above sections of this review.