Things you can do to make post op MRI better
- At MRI, titanium and vitallium hardware produce fewer artifacts than stainless steel.
- Short time inversion recovery (STIR) sequences should be used for fat suppression, since sequences based on selective fat saturation pulses are associated with poor homogeneity
- The phase encoding direction in both the axial and sagittal planes should be parallel to the long axis of the orthopedic material, since the artifact produced will be linear and parallel to the metal material, therefore with less interference with image assessment
Causes of failed surgery
- Early causes
- Malpositioning of orthopedic hardware
- Hemorrhage
- Infection
- Pseudomeningocele
- Surgery at a wrong level
- Canal or foraminal stenosis
- Textiloma
- Late causes
- Fracture of orthopedic hardware
- Failed fusion and pseudoarthrosis
- Spondylolysis and spondylolisthesis
- Osteophytosis
- Sterile arachnoiditis
- Recurrent disc herniation
- Fibrosis
Post discectomies
- Findings in the early postoperative period (six months) require cautious evaluation
- MRI No C
- Early postoperative changes following discectomy may simulate the previously removed herniated material as a result of the disruption in the fibrous annulus and the presence of epidural edema.
- In the area of laminectomy, the dural sac may slightly bulge through the bone defect, which should not be confused with a pseudomeningocele
- MRI+C
- The homogeneous enhancement of this fibrosis and granulation tissue explains the observed mass effect that will progressively decrease
- Edema and enhancement
- Of the vertebral endplates are observed in 19% of patients between 6 and 18 months following surgery.
- In 20-62% of patients, enhancement of the nerve roots is observed between 3 and 6 weeks following surgery.
- This enhancement progressively decreases, and therefore any enhancement observed after six is considered pathological.
- Enhancement associated with bacterial discitis is typically more intense than that reported during the normal postoperative period in asymptomatic patients
- A fluid collection with a paraspinal or anterior epidural location or located adjacent to the disc involved and enhancement of the psoas are usually indicative of infection.
Textiloma
- The textile surgical material accidentally left behind in a surgical bed may become a textiloma
- This material usually contains a radiopaque marker that is readily visible on X-ray and CT.
- This marker cannot be assessed in MRI studies because it is a barium sulfate filament that is not paramagnetic
- T2-weighted sequences demonstrate hypointense lesions with peripheral foreign body reaction, and show enhancement of the peripheral inflammatory tissue after contrast agent administration
- One month after surgery, the patient is readmitted due to severe pain and tumefaction in the surgical area. The MRI study demonstrates a hypointense lesion (asterisk) on the T2-weighted sequence (A) compatible with a foreign body, with peripheral enhancement of the reactive inflammatory tissue (arrows in B) on the T1-weighted sequence following contrast agent administration, compatible with textiloma.
Epidural fibrosis
- Caused by scarring tissue formation in the epidural space after spine surgery.
- Since epidural scarring is part of the normal reparative mechanism of tissue after surgery,
- Most patients with epidural fibrosis are asymptomatic
- There is controversy regarding the involvement of epidural fibrosis in the failed back surgery syndrome.
- Multicenter studies have demonstrated that extensive epidural fibrosis patients are 3.2 times more likely to experience recurrent radicular pain.
- Fibrosis-induced pain may be due to irritation, compression and traction of the fibrotic tissue on adjacent nerve structures.
- Outcomes after reintervention in patients who only presented with fibrosis are worse than in patients with associated recurrent disc herniation (DH).
- Consequently, the presence of associated conditions associated in patients with postoperative lumbar pain and fibrosis should be ruled out.
- The main differential diagnosis of epidural fibrosis is recurrent DH.
- On CT images,
- Recurrent DH shows higher attenuation, 90-120 Hounsfield units (HU), whereas fibrosis shows 50-75 HU.
- Intravenous contrast-enhanced MRI is the modality of choice to differentiate fibrosis from DH with a sensitivity of 96%, which increases in T1-weighted fat-saturation sequences.
- At MRI, fibrosis is isointense on T1-weighted and variable on T2-weighted sequences, with immediate homogeneous enhancement, and may be associated with adjacent nerve root thickening
- Recurrent DH may show early peripheral and late central enhancement (30 min after contrast agent administration) by diffusion of the contrast material into the center of the disc
- Symptomatic epidural and perineural fibrosis. 37-Year-old female who underwent follow-up MRI for persistent lumbar pain one year and a half after surgery involving right hemilaminectomy and L5-S1 discectomy. Unenhanced and contrast-enhanced axial T1-weighted sequences (A and B) demonstrate diffuse enhancement of the epidural and perineural fibrosis tissue around the right S1 nerve root (arrows).
Recurrent disc herniation
- Recurrent DH is involved in 7-12% of cases of recurrent lumbar pain following spine surgery.
- MRI is the modality of choice for assessment of recurrent DH and the protocol should include T1-weighted and T2-weighted sequences on the axial and sagittal planes, as well as contrast-enhanced T1-weighted sequences.
- The herniated disc tissues are isointense with reference to the parent disc, but they may appear hypointense on T1-weighted sequences if calcified or associated with an ex vacuo phenomenon.
- After contrast administration, the disc material is not immediately enhanced, and peripheral enhancement is observed because of the granulation or dilated tissue of the adjacent epidural plexus
- Persistent/recurrent disc herniation. 48-Year-old female who underwent laminectomy and L5-S1 discectomy. Follow-up MRI was performed 20 days after surgery due to persistent lumbar pain radiating to the left lower extremity. The axial T2-weighted image (A) shows persistent-recurrent left parasagittal DH connected to the left S1 nerve root at the lateral recess level (arrow). Unenhanced and contrast-enhanced axial T1-weighted image (B and C) shows peripheral enhancement of the herniated material.
Pseudomeningocele
- Pseudocyst, which has no true meningeal lining, secondary to a postoperative dural dehiscence.
- Pseudomeningocele affects 0.19-2% of patients after lumbar laminectomy.
- The size of a pseudomeningocele may vary from 1 to 10 cm.
- Small pseudomeningoceles may heal spontaneously, whereas large ones typically require surgery for the closure of the defect, and may be associated with headache induced by intracranial hypotension
- Although most patients are asymptomatic, some may have symptoms related to compression and entrapment of adjacent nerve roots.
- MRI is the modality of choice and shows on all sequences an isointense cystic lesion filled with cerebrospinal fluid (CSF).
- Communication of the cyst with the thecal sac can be observed on T2-weighted sequences as an area of lower signal intensity due to the higher flow of CSF along this communication.
- 36-Year-old female who underwent surgery for L5-S1 disc herniation. Postoperative MRI image with axial T2-weighted sequence, which demonstrates a postoperative pseudomeningocele on the bed of the left S1 laminectomy (arrow).
- MRI sensitivity is higher than sensitivity of any other imaging techniques, and allows for visualization of the communication between lesion and thecal sac (asterisk).
- After contrast administration, a fine peripheral enhancement can visible. If a more intense enhancement is visualized, superinfection of the pseudomeningocele should be ruled out
- (A) showed a superinfected pseudomeningocele with decreased focal signal intensity (arrow) due to flow of CSF in the region of the dural tear and marked wall enhancement on pre-contrast and post-contrast T1-weighted sequences (asterisks on B and C).
- In cases of large lesions with subcutaneous extension, enlargement of the window may be necessary to avoid artifacts and poor homogeneity produced by the surface coil.
Postoperative infection
- Symptoms of postoperative infection are usually nonspecific;
- Should be suspected in patients with increased lumbar pain after surgery and in patients with abnormal laboratory tests such as increased C-reactive protein.
- Initially, postoperative infection originates as discitis, and less commonly, as facet joint infection, and it may extend into adjacent structures.
- Most commonly
- Staphylococcus aureus
- Staphylococcus epidermidis.
- Xray
- At early stages: no changes are observed
- At later stages: lysis and erosion of the endplates adjacent to the affected disc can be observed
- MRI
- Contrast-enhanced MRI with fat saturation
- Modality of choice
- Allows for the evaluation of the bone edema and discitis earlier than other imaging techniques.
- Diffusion-weighted MRI images show hyperintensity of the central necrotic region of the abscess and hypointensity on the apparent diffusion coefficient (ADC) map.
- CT
- Allows for assessment of
- The associated bone involvement,
- Phlegmonous collections (seen as hyperenhancing soft-tissue lesions),
- Abscesses (hypodense collections with peripheral enhancement).
- CT and ultrasonography are usually used as guides for biopsy.
Arachnoiditis
- The incidence of this complication is 3%,
- Excluding lesions caused by a previous myelography.
- Not a common finding,
- CT
- Calcifications (calcified arachnoiditis) can be seen.
- MRI
- Modality of choice: axial T2-weighted FSE sequences is the optimal
- There are three patterns of presentation.
- Type 1
- Designates a conglomerate of nerve roots a and is suggestive of mild involvement.
- Type 2
- Peripheral adhesions of the nerve roots to the thecal sac, giving rise to an ‘‘empty-sac’’ appearance.
- This pattern is associated with moderate involvement.
- Type 3
- Refers to an intermediate attenuation mass obliterating the subarachnoid space below the conus medullaris, being the most severe presentation
- Sagittal and axial T2-weighted sequences (A and B) that demonstrate hypointense tracts within the thecal sac that divide the arachnoid space with CSF loculation (arrows). Post-contrast T1-weighted sequences (C) demonstrate meningeal and root enhancement with peripheral distribution (dashed arrow)
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