Evaluation of Spine Infections in Children

Examination

Spine infections in children

• Complete neurological examination including assessment of rectal tone: Children with suspected spinal infections should be checked for detailed motor responses and sensory levels (temperature, pin-prick, and proprioception) to determine current status and postsurgical expectations. Deep motor reflexes as well as sphincter reflexes should be examined. Rectal examination should be documented.
• Pain may confuse examination: Signs of neurological deficit should be noted. However, pain- limited weakness can be expected.

Spinal epidural abscesses in children

• 78% have neurological sign: 70–78% of children suffer neurological compromise prior to surgical decompression (20, 37).

Spinal subdural abscesses in children

• No characteristic presentation: There is no pathognomonic presentation pointing to the diagnosis of spinal subdural infection. Authors who have reviewed these infections in adults stress the importance of fever, back or neck pain, and rapidly developing signs of spinal cord compression as suggestive of the diagnosis (21, 28, 120).

Intramedullary spinal cord abscesses in children

• Neurological deficits: Children with intramedullary spinal cord abscesses often have neurological signs localizing the lesion. Assess motor strength and sensation in all four extremities. Sphincter tone and reflexes should be examined. If the child is ambulatory, assess the gait. If continent of urine, assess for new incontinence. Palpate the spine to elicit tenderness.

Laboratory Tests

Spine infections in children

• CBC, ESR, and CRP: The diagnostic workup of pyogenic spine infections should include a CBC, ESR, and CRP. CRP levels normalize faster than ESR levels, and thus CRP levels are a useful modality to determine efficacy of treatment. In a review by Fernandez et al. (6), the mean WBC count at admission in children with diskitis was 10,900/ml (range: 7500–25,400), and the mean ESR was 42 mm/hour. Similarly, in patients with vertebral osteomyelitis, the mean WBC count was 12,600/ml (range: 4300–23,000), and the mean ESR was 45.6 mm/hour (range: 9–100). In a case series of children with spinal epidural abscesses, Auletta and Chandy (9) reported only 3 of 8 patients had an elevated WBC count (mean, 13,900 cells/ml). However, many children had thrombocytosis (mean, 439,000 platelets/ul) and elevated ESR levels (mean, 58.6 mm/hour) and CRP levels (mean, 6.5 mg/L).
• Blood cultures: Blood cultures should be obtained when an infection of the spine is suspected.

Spinal epidural abscesses in children

• CBC, ESR, and CRP: Leukocytosis is common during the acute phase of epidural abscesses, but it usually normalizes in chronic cases (21). ESR (usually over 30 mm/hour) and CRP levels are elevated, and thrombocytosis is present (28). In adults, WBC counts greater than 14,000/ml on admission and persistently elevated CRP measurements between days 8 and 14 of admission have been correlated with poor outcomes (48).
• Lumbar punctures problematic: Lumbar puncture should be avoided in patients with spinal epidural abscess for fear of spreading infection to the subarachnoid space and the possibility of causing pressure gradients above and below the abscess (20). However, because the clinical presentation can be similar to that of meningitis, lumbar puncture is occasionally performed in these patients prior to establishing the diagnosis of epidural abscess. In these cases, the results may range from frank pus to mild leukocytosis, low glucose and/or elevated protein. Of note, a markedly elevated CSF protein may signify a complete obstruction proximal to the location of the tap (22, 42).
• Positive blood cultures: Blood cultures are positive in 67–82% of cases (37, 49).
• Abscess cultures: Abscess cultures are positive in 82–90% of cases (42, 47).

Spinal subdural abscesses in children

As with the clinical features, laboratory data in children with spinal subdural infections may be helpful but remain non-specific (28).

• CBC, ESR, and CRP: Blood leukocyte count, ESR, and CRP are usually elevated but are not sensitive indicators of spinal infections (115, 116).
• Blood cultures: Although the concordance rate between blood cultures and spinal subdural abscess cultures has not been studied, the relatively high concordance between epidural abscesses and blood cultures (approaching 100% in some studies) argues for the inclusion of blood cultures in the diagnostic work-up of any spinal infection (109, 117). However, in cases where clinical and radiographic suspicion is high, waiting for blood cultures to return before commencing treatment can be dangerous.
• Lumbar punctures controversial: The usefulness of lumbar puncture in the diagnosis of spinal subdural infection is controversial. Changes in CSF cell count, glucose, and protein cannot reliably differentiate a subdural abscess from meningitis. Furthermore, organisms in an encapsulated infection may “hide” from the CSF obtained via lumbar puncture, thus limiting its diagnostic yield (111, 113). Rarely, a lumbar puncture performed perfunctorily may also confound the diagnosis by seeding new skin flora into the subdural space (106, 108, 112). Moreover, a lumbar puncture may cause irreparable neurological damage if performed on a child with an abnormally low-lying spinal cord. Finally, there exists the theoretical risk of downward spinal coning following lumbar puncture below the level of a large abscess, causing a complete subarachnoid block (110, 114).

Intramedullary spinal cord abscesses in children

• CBC, ESR, and CRP: The assessment of a patient suspected of harboring an intramedullary spinal cord tumor should include a CBC, ESR, and CRP to evaluate for infection and trend the response to treatment. CSF studies may demonstrate elevated protein and white blood cells, but a normal cell count and the absence of pleocytosis do not rule out an abscess.  
• Blood cultures and cultures from the abscess: Blood cultures and cultures from the abscess during open surgery or guided aspiration are necessary to determine adequate antimicrobial treatment.

Radiologic Tests

Spine infections in children

• PA and lateral radiographs of the spine: This is recommended as an initial study. Disk space narrowing and irregularities of endplates take 2–3 weeks to develop radiographically after the initial onset of symptoms (82).
• MRI: MRI with gadolinium contrast is deemed the gold standard for evaluation of spinal infection. Decreased vertebral endplate signal is noted on T1-weighted images, and increased disk signal and increased vertebral endplate signal are apparent on T2-weighted images. Enhancement of the disk and vertebral body is noted with contrast. MRI scans have been found to be as sensitive as 96% and to have a specificity of 93% for diagnosing of vertebral osteomyelitis, making MRI more sensitive and specific than either plain radiographs or radionucleotide scans (82).

Spinal epidural abscesses in children

The majority of cases have a posterior location in children, generally in the lumbar region. Imaging studies will reveal an average vertebral extent of 5.4 bodies (22). Distant sites of osteomyelitis can be missed if only MRI of the spine is performed.

• Ultrasound: Ultrasound is useful in premature infants and neonates for the diagnosis of cord compression and epidural collections (19, 51).
• Plain x-rays: Roentgenograms offer little in terms of diagnosis unless a vertebral osteomyelitis accompanies the abscess (4, 35). Plain x-rays are informative only in 44–65% of cases (50).
• CT scans: CT myelography was once the standard radiological evaluation used for spinal epidural abscess, but it has been replaced by the MRI. It is still used when MRI is unavailable or cannot be used (47). CT scans may, however, fail to delineate the extent of abscess involvement if a complete myelography block exists, and the test can be complicated by bleeding, spread of infection, and neurological deterioration secondary to pressure gradient changes about a complete block (21, 50).
• MRI: Gadolinium-enhanced MRI is the study of choice in patients with spinal epidural and subdural abscesses. MRI reveals or suggests the diagnosis in more than 91% (17, 21, 44). On T1-weighted imaging the abscess will appear as a hypo- or isointense epidural mass, and any associated vertebral osteomyelitis will show as a reduced signal in the bone (52). On T2-weighted MRI scans there will be a high intensity epidural mass that often enhances with gadolinium. Vertebral osteomyelitis shows up as increased signal in bone on T2-weighted images (52). Postcontrast MRI scans show the best anatomical relationship between the abscess wall and dura, and can eliminate other possibilities such as disk herniation, syrinx, spinal tumor, spinal hematoma, cord infarct, and transverse myelitis (17, 21, 53, 54).

T2-weighted sagittal MRI of epidural abscess: Arrow shows hyper intense epidural collection of epidural abscess.

Spinal subdural abscesses in children

• Myelogram or MRI: MRI or a myelogram, or both, will usually outline the extent of a subdural abscess (95). A subdural collection or mass with decreased signal on T1-weighted images and increased signal on T2-weighted sequences strongly suggests abscess (94). MRI typically shows a thin, elongated, and ring-enhancing fluid collection in the subdural space The dura covering the collection may be thickened, with the underlying subarachnoid space narrowed or obliterated (96). Occasionally, differentiating between subdural and epidural infections on MRI may be challenging (93). A hypointense rim of inflamed dura, absent from subdural infections, may be seen in epidural infections (93). Additionally, the use of fat-suppression techniques for subtraction of marrow and epidural fat may help better define the subdural infection (94). Otherwise, axial imaging may be more useful for confirming the subdural location of the collection (96).

Intramedullary spinal cord abscesses in children

• T2-weighted images show high signal lesion: Spinal abscesses typically produce high signal intensity on T2-weighted images.
• T1-weighted images with contrast: The gold standard imaging modality for suspected intramedullary spinal cord abscesses is the gadolinium-enhanced MRI. Intramedullary abscesses typically demonstrate marginal enhancement with central low signal intensity on T1-weighted imaging with gadolinium27. However, a ring-enhancing mass is a nonspecific imaging finding, with a broad differential diagnosis, including primary or secondary cord tumors (necrotic glioma, metastases), resolving hematoma, infarction, and demyelinating disease (104).
• Role of diffusion-weighted MRI: Two recent reports suggest that increased diffusion on DWI may be helpful in differentiating intramedullary abscess from tumor (67, 104).

Spinal cord tethered by dermal sinus and containing an intramedullary abscess: Tethered spinal cord due to dermal sinus (arrow in b) with secondary infection resulting in an intramedullary abscess, arachnoiditis and cord swelling. Shown are (a) a T1-weighted MRI (b) a T2-weighted MRI, and (c) an enhanced T1-weighted image.

Nuclear Medicine Tests

Spine infections in children

• Not indicated: Gallium and technetium 99-m bone scans were used in the past. However, due to a nonspecific uptake and the inability to differentiate between diskitis and vertebral osteomyelitis, these nuclear tests are no longer preferred. MRI is the diagnostic imaging of choice.

Spinal epidural abscesses in children

• 67–75% positive bone scans: Nuclear bone scans are not specific and are positive in only 67–75% of cases (94). 99Tc scans of bone may confirm the diagnosis if distant osteomyelitis is suspected (95),

Spinal subdural abscesses in children

• Labeled WBCs for fevers of unknown origin: Indium-111-labeled WBC scintigraphy may be useful in identifying spinal subdural infections in children with fevers of unknown origin and negative blood, urine, and sputum cultures (95).

Intramedullary spinal cord abscesses in children

• Labeled WBCs for fevers of unknown origin: Indium-111-labeled WBC scintigraphy may be useful in identifying spinal subdural infections in children with fevers of unknown origin and negative blood, urine, and sputum cultures (95).

Electrodiagnostic Tests

EMG and NCS are too nonspecific to diagnose spinal infection.

Neuropsychological Tests

Spine infections in children

• Not indicated

Spinal epidural abscesses in children

• Not indicated

Spinal subdural abscesses in children

• Useful to follow treatment impact: For those children harboring spinal subdural infections with concomitant spinal dysraphisms, post-treatment neuropsychological testing may be beneficial to document improvement and return to pre-infection state. Children with dysraphisms with or without hydrocephalus usually have average to low-average intelligence but are prone to visuomotor deficits and delayed school progress, especially in arithmetic (98).

Intramedullary spinal cord abscesses in children

• Useful to follow treatment impact: For those children harboring spinal intramedullary infections with concomitant spinal dysraphisms, post-treatment neuropsychological testing may be beneficial to document improvement and return to pre-infection state. Children with dysraphisms with or without hydrocephalus usually have average to low-average intelligence but are prone to visuomotor deficits and delayed school progress, especially in arithmetic (98).

Correlation of Tests

• Symptoms at presentation and MRI