Continuing Education Activity

Intramedullary spinal cord abscess (ISCA) is a rare central nervous system infection associated with high mortality and neurological morbidity. Though rare, prompt diagnosis and treatment of this condition are of paramount importance to preventing damage to the spinal cord that can lead to disabling neurological deficits and possibly death.ISCA should not be confused with a spinal epidural abscess which is far more common. Abscesses can be either primary (source of infection not identifiable) or secondary (the source is identifiable). Multiple abscesses occur in around 26% of cases. This activity outlines the evaluation and treatment of spinal cord abscesses and explains the interprofessional team's role in managing those with this condition.

Objectives:

• Describe the common etiologies of intramedullary spinal cord abscesses.
• Review the steps for complete evaluation and workup for patients presenting with intramedullary spinal cord abscesses.
• Outline the appropriate treatment options for a case of intramedullary spinal cord abscess.
• Explain the significance of collaboration and communication among the interprofessional team when diagnosing and treating patients with intramedullary spinal cord abscesses.

Introduction

First described by Hart in 1830, in the present era, an intramedullary spinal cord abscess (ISCA) is a very rare form of spinal cord abscess.[1][2][3]

Their rarity may be accountable to the following factors:

1. A relatively smaller volume and total surface area of the cord.    
2. An acute angle of origin of the corresponding spinal arteries.       
3. The protection is provided by the osseous vertebral canal and the meningeal layers, notably the pia mater.[4]

Though rare, prompt diagnosis and treatment of this condition are of paramount importance to preventing damage to the spinal cord that can lead to disabling neurological deficits and possibly death. 

Etiology

Currently, almost 40% of ISCA are cryptogenic.[2][5][6] Among 54 cases of ISCA reviewed between 1977 and 2009, only 9% of them were cryptogenic.[7]

Congenital dermal sinus (CDS) is a common cause of ISMA among children, whereas hematogenous spread is the main pathogenesis among adults.[2] CDS accounts for 45% of ISCA in pediatric cohorts, compared to 24% in adult patients.[8] CDS is most commonly located in the lumbosacral region (90%).[9] CDS may be associated with concurrent lesions such as dermoid, epidermoid, and retained medullary cord.[8][10]

Hematogenous spread is the main pathogenesis among adults.[2] This results from septic emboli from extraspinal sources such as urogenital sepsis, infective endocarditis, and pneumonia.[8][11]

Staphylococcus, Streptococcus, and coliform bacteria have been observed to be the most common microbiological causative organisms.[8] Staphylococcus aureus is invariably associated with ISCA relating to congenital dermal sinuses.[9]

Multiple abscesses occur in around 26% of cases.[6]

Epidemiology

Since Hart initially described the diagnosis in 1830, there have been at least 137 cases of ISCA reported in the medical literature.[7] The age distribution for those with ISCA is bimodal, most commonly occurring in the first and third decades of life. Also, men are more commonly afflicted than women. It is uncertain whether this condition is more common in the United States than elsewhere in the world per capita or whether some races are more likely to be afflicted by ISCA than others.

Pathophysiology

To remain viable, the spinal cord requires the perfusion of its tissues with blood. When the pia mater is violated, or a patient acquires an infection in the bloodstream, the pathogen may penetrate the blood-cord barrier. As a part of the central nervous system, the blood-cord barrier is functionally equivalent to the blood-brain barrier, leaving a certain segment of the population - especially those who are immunocompromised or intravenous drug users - at risk of developing an infection of the spinal cord due to mechanisms similar to those that may cause a brain abscess.[12]

Abscesses can be either primary (source of infection not identifiable) or secondary (the source is identifiable).[13][14]

The pathogenesis postulated for ISCA include:       

1. Hematogenous dissemination and bacterial embolism from an extraspinal infection.   
2. Contiguous extension.   
3. Direct implantation (penetrating trauma, neurosurgical procedures-lumbar puncture, and intrathecal morphine pump).     
4. Cryptogenic.[6][13][15][16][17]

The watershed zone makes the dorsal cord and thoracic spine more prone to ISCA.[8][14]

The fulminant neurological sequelae observed in ISCA are secondary to the mechanical-vascular insult of the spinal cord by the abscess and its resultant edema superimposed by the relatively compromised vascularity of the spinal cord.[14][15]

Risk variables for the development of ISCA described in the literature include:

• Spinal dysraphism and CDS.[18]
• Epidermoid cyst.[19]
• Vertebral osteomyelitis discitis spondylodiscitis and epidural abscesses.[3][20][21]
• Infective Endocarditis.[22][23]
• Spinal infarction due to spinal artery embolism by bacterial embolism.[7]
• Spinal artery occlusion.[7]
• Spinal dural arteriovenous fistula (SDAVF) leads to chronic venous congestion disrupting the blood–spinal cord barrier.[24]
• Right to left cardiac shunts such as Patent foramen ovale and right superior vena cava (RSVC) drain into the left atrium.[5][25]
• Penetrating injury.[26][27]
• Intravenous drug users.
• Prior history of neurosurgical trauma or surgery.
• Immunocompromised state.[13]

In a modern-era review of ISCA   

• 44% of ISCA was associated with anatomical abnormalities 
• 24% of ISCA was from the contiguous spread      
• 8% of ISCA was secondary to hematogenous dissemination and      
• 64% of them were cryptogenic.[6]

History and Physical

The pattern of clinical presentation in ISCA can be categorized as follows:     

• Acute (less than one week)      
• Subacute (1 to 6 weeks), and        
• Chronic (more than six weeks).[6][14]

ISCA is more frequently observed among males, with a peak incidence in the first and third decades of life.[14] Women have slightly higher risk preponderance during the first four decades, whereas it has been observed to be constant in men throughout their lifetime.[6]

The characteristic triad in ISCA constitutes fever, pain, and neurological deficits.[16] But this is not present in all patients and is invariably absent in subacute or chronic cases.[6] Accompanying fever may or may not be present.[2]

ISCA mimics acute transverse myelitis in the acute stage. Chronic ISCA mirrors spinal cord tumors and chronic myelopathy.[2][6][8][28]

Children often have rapid symptomatology.[13] Adult cohorts, however, most often show an insidious onset of symptoms.

Among children, the median age of presentation is three years.[8] Only one-third of children have a fever during the initial presentation. Neurological deficit is the most common presenting feature observed in almost 90% of them.[8] Meningism is observed in approximately 20%, and elevated laboratory markers (white blood cell counts, C-reactive protein concentration, and erythrocyte sedimentation rate) are observed in approximately 55%.[4] An abnormal CSF study is observed in around 80% of cases.[6] They present in acute, subacute, and chronic stages in approximately 40%, 33%, and 21% of cases, respectively.[4]

The typical symptomatology among children with ISCA includes:       

• Motor deficits (90%)   
• Infection signs (86%)  
• Sensory deficits (40%)   
• Urinary dysfunction (44%) and     
• Bowel dysfunction (18%).[4]

Among 38 cases of pediatric IASC studied between 1875 and 2001, 45% were female.[29] The median age of presentation was 36 months. 53% of them had concurrent defects such as CDS.[29] 89% of them presented with neurologic deficits.[29] 33% of them initially presented with fever.[29] 

Among 26 cases of ISCA reviewed between 1998 and 2007, the most common clinical characteristics were:

• Motor deficits
• Fever
• Pain, and
• Bladder dysfunction[30]

Of these, 68.5% were males, with a median age of presentation at 32 years. Fever was the initial presentation in 43.4%.[7] The presentation patterns as acute, subacute, and chronic were observed in 44.4%, 16.7%, 31.5%, and 7.4% of cases, respectively.[7]

In the most recent systematic review comprising 137 ISCA cases from 1949 to 2022, 50.03% were adult cases, and 78.5% were males. The median age at the presentation was 52 years.[6] The patterns of the clinical presentation were as acute, subacute, and chronic in 37%, 28.5%, and 20%, respectively.[6] 

The most common patterns of clinical presentations include:     

• Motor impairment (99%)   
• Sensory loss (87%)  
• Pain(56%)
• Urinary involvement (50%)[6]

Evaluation

Elevation in the laboratory markers of inflammations (white blood cell counts, C-reactive protein concentration, and erythrocyte sedimentation rate) is observed in 54%.[4] An abnormal CSF study is observed in 78%.

Magnetic resonance imaging with contrast study is the gold standard radioimaging modality.[15] ISCA typically shows hyperintensity on T2 and has a characteristic ring-enhancing pattern in contrast imaging.[15][28] An early stage of an abscess may have a more patchy and ill-defined enhancement, while the late stage of the abscess shows a characteristic peripheral ring enhancement.[8] Following antibiotic therapy, the abscess typically decreases in size with a concurrent reduction in T2 hyperintensity.[13] MRI also reveals cord edema, spinal dysraphism, as well as secondary syrinx. This also provides a detailed anatomical extent of the CDS and concurrent pathologies.

Diffusion restriction on diffusion-weighted MRI is beneficial in differentiating ISCA from a tumor and other differentials.[8][16]

'Drop sign' or precipitation is characteristically observed in an intramedullary tubercular abscess.[28][31]

Indium-111 labeled WBC scintigraphy is very useful for evaluating patients with ISCA presenting as pyrexia of unknown origin.[8]

Treatment / Management

A prompt and timely surgical intervention followed by appropriate antibiotic therapy (minimum of 6-8 weeks) is the mainstay of management.[2][8][29] Diagnostic and therapeutic drainage of the abscess can be undertaken by open surgical myelotomy or navigation-guided needle aspiration.[16] Common surgical strategies include laminectomy/laminoplasty followed by limited midline myelotomy and evacuation of the abscess.[28][32] In spinal dysraphism, drills are usually avoided during laminectomy to prevent accidental entanglement of the sinus tract within the drill bit, which is a harbinger of the risk of cord injury.[8] Complete surgical excision of the CDS and its tract is recommended.[9]

Fluorescein aids in localizing and planning surgical strategies.[33] Intraoperative ultrasound is a valuable armamentarium for determining the site and extent of durotomy and myelotomy, especially in multi-loculated abscesses.[8] Intraoperative neuromonitoring such as motor-evoked potentials (MEP), somatosensory evoked potential (SSEP), electromyography (EMG) with sphincter monitoring, and D-wave monitoring are essential adjuncts, especially while attempting to remove the infected dermoid cyst.[8] Midline myelotomy is undertaken at the region of maximum cord edema with the thinnest overlying pial layer. A ventricular catheter can be gently negotiated to break the loculi. The abscess cavity is then generously irrigated with the antibiotic-saline solution.[8]

Sometimes intraoperatively, instead of frank pus, solid inflammatory tissue, and antibioma may be encountered and has to be biopsied and safely excised.[9] In cases of holocord ISCA, limited myelotomy with aspiration and drainage aided with a catheter or a feeding tube is advised.[2][34][35] The use of the ommaya reservoir for frequent post-operative aspirations has also been mentioned.[36] Expansile duraplasty, either by artificial dural substitutes or harvested thoracolumbar or fascia lata, is then undertaken to nullify the damaging consequences of cord edema.[8] Osteopathic laminoplasty is recommended in children to prevent scoliotic spinal deformities in the future.[14]

A recent systematic review found that laminectomy and myelotomy were undertaken in 58.5% of cohorts, and stereotactic needle aspiration was performed in 62.8% of the same.[6]

Prophylactic complete resection of CDS has been advised to prevent catastrophic complications in the future.[14][9] Cautious use of steroids to minimize cord edema and inflammation can be undertaken.[8][14]

Almost 25–40% of ISCA is sterile.[6][8][14] A review study of 26 cases between 1998 and 2007 had S. aureus as the sole etiological agent.[15]

Skin commensals (S. epidermides, S. aureus), Enterobacteriaceae, and anaerobes are commonly involved in CDS.[6][13] Enteric Gram-negative rods are implicated in lumbar ISCA. [6] 

Microbiological agents implicated in the causation of IMSA include:

• Staphylococcus (25%)      
• Streptococcus    
• Escherichia coli     
• Proteus   
• Listeria
• Schistosomiasis   
• Bacteroides     
• Pseudomonas    
• Brucella
• Hemophilus    
• Histoplasma    
• Actinomyces     
• Mycobacterium tuberculosis
• Fungal infections[6][16][29][37][38][39][40]       

Early broad-spectrum empirical antibiotics effective against Staphylococcus, Streptococcus, enteric Gram-negative bacilli, and anaerobes should be promptly initiated.[6][30] A minimum of 4 to 6 weeks of parenteral antibiotics is advised.[6][40] The combination of vancomycin, metronidazole, and cefotaxime is currently the most preferred.[8] Intravenous antibiotics are usually administered for 4 to 6 weeks, followed by extended oral coverage for a minimum of 2 to 3 months.[8]

A recent systematic review has shown antibiotics usage in only 87% of cohorts with 137 cases of ISCA.[7]

Differential Diagnosis

• Acute transverse myelitis
• Tuberculomas
• Hypervascular neoplasm (ependymoma, hemangioblastoma, astrocytoma)
• Metastatic lesions (renal cell carcinoma)
• Demyelinating lesions
• Resolving hematoma
• Cord infarction
• Neurocysticercosis
• Schistosomiasis
• Type I dural fistula
• Cavernous malformations[8][7][13][16][24][41]

Decreased diffusivity within the cavity of ISCA on DWI and the rapidly progressive nature of the lesion is crucial in differentiating it from other clinical mimics.[16]

Prognosis

Neurological recovery in ISCA depends on the rapidity of diagnosis, promptness of surgical intervention, and the institution of appropriate antibiotics.[8]

Among 38 cases of pediatric IASC studied between 1875 and 2001:

• Complete neurologic recovery in 18%
• Mild neurologic impairment in 39%
• Severe neurologic impairment in 11%
• Death in 21% of the cohorts was observed[29] 

In the latest systematic review of 137 cases:

• Recovery of 20%    
• Residual deficits 17.1%      
• Persistent deficits 40%, and       
• Death in 14.2% of the cohorts was observed[6]

Children with ICSA secondary to infected dermoid cysts have a chance of neurological improvement of less than 20%. The presence of fever and limb weakness has been observed to have high odds of poor clinical results.[42]

Due to the advancement of medicine in the areas of antibiotics, radiology, and surgery, the mortality rate for ISCA has gone from 90% between 1840 and 1944 to 4-8% between 1998 and 2007.[6][7][30] Paradoxically, the reported incidence of persistent neurologic deficits is still as high as 40 to 70%.[2][43] These neurological sequelae may be treated with physical medicine and rehabilitation.

Complications

The neurological sequelae in the patients can result from:

• Mechanical compression.
• Septic thrombosis causing spinal cord infarction.
• Syrinx formation[44]

The inadvertent rupture and dissemination of the abscess can lead to the following:

• Meningitis.
• Brain abscess.
• Meningoencephalitis.
• Sepsis.
• Mortality[7]

Postoperative and Rehabilitation Care

The most significant variable governing the clinical outcomes in children with ISCA is the presence of paralysis which is seen in almost 60%.[29] Physical Medicine and Rehabilitation specialists may be helpful for patients with reduced mobility or compromised functionality.

Follow-up with clinical and MRI imaging within the first year of surgery is advocated to rule out recurrence, which is observed in almost 25% of cases.[6][8][29] Long-term follow-up is also advocated due to its potential for late recurrence.[9]

Consultations

Potential consultations may involve a neurologist, a neurosurgeon, a neuroradiologist, an infectious disease specialist, a neuropathologist, and a rehabilitation doctor.

Deterrence and Patient Education

Patients will need to understand the nature and severity of their condition and the treatment options based on the precise nature of their abscess. If the abscess is pressing on the spinal cord, they will need surgery and instruction on how to proceed post-laminectomy. If the abscess is causing neurological symptoms or cauda equina syndrome, they will need to understand the emergent nature of this condition and have emergent treatment. Post-surgical rehabilitation will require the patient to comply with all therapeutic activities. If surgery is unnecessary, they will be instructed regarding how to proceed with their antibiotic regimen. Spinal dermal sinus tracts should be operated on as soon as possible.[45] Complete resection of the dermal sinus before six months of age may prevent the formation of IASC.[29]

Enhancing Healthcare Team Outcomes

ISCA is an enigmatic clinical entity with the tendency for multispectral patterns of presentations such as:

• Acutely mimicking transverse myelitis.
• Progressive dorsal pain with neurological deficits
• Insidious pattern, mimicking a spinal tumor or chronic myelopathy[6][46]

An interprofessional team comprising a neurologist, a neurosurgeon, a neuroradiologist, an infectious disease specialist, a pathologist, and a rehabilitation specialist is essential for managing ISCA.[6][46] Nurses and pharmacists, particularly infectious disease specialty pharmacists, round out the interprofessional team. ISCA is currently limited to approximately 137 cases in the literature, so it is a poorly studied entity. Thus, diagnosis, treatment, and prognosis recommendations are mostly limited to Level 5 evidence. Due to the close kinship between the approach to the far-more-common spinal epidural abscess and that of ISCA, a good strategy would be to do what we would ordinarily do to rule out the former while being open to the possibility that the latter may be the culprit lesion.[47]

The prognosis is good, with prompt surgical treatment and antibiotics. However, the size, location of the abscess, and severity of the neurological deficits determine the eventual outcome. Despite advances in treatment, spinal cord abscess still carries a mortality of 4 to 8%, and most patients are left with some type of residual neurological deficit. Therefore intensive neuro-rehabilitation is invariably justified.[15] Recurrence of the abscess has been noted in most series, and hence, serial neurological and radio imaging are advocated during their follow-up.[48][49]