Differential Diagnosis of Surgical Disorders of the Spine

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Chapter 4 Differential Diagnosis of Surgical Disorders of the Spine

Establishing a differential diagnosis of spine pathology starts with the characterization of pain, associated signs and symptoms, and evaluation of any presenting neurologic deficit. Special attention must be paid to the warning signs and symptoms of back pain (Box 4-1), which helps to identify more serious pathology.1 Assessment of pain in conjunction with fever and weight loss, recumbent position, morning stiffness, acute onset, or visceral component allows for initial categorization. With this information, further laboratory and radiologic evaluation can proceed, and ultimately, a diagnosis with appropriate surgical or medical management can usually be achieved.

This chapter presents a systematic approach to evaluating a patient with a suspected spine disorder (Box 4-2). The first portion of this chapter addresses disorders that usually present with spinal pain, and the second half deals with conditions that present with pain and neurologic deficit.

BOX 4-2 Differential Diagnosis of Surgical Disorders of the Spine

Spinal Pain

Pain Associated with Fever and Weight Loss

Infectious or neoplastic processes are potential etiologies in patients who present with fever, weight loss, and spinal pain. The most common infectious conditions affecting the spine include vertebral osteomyelitis, discitis, epidural abscess, and granulomatous processes. Neoplastic processes may have similar presentations. Failure to uncover the etiology may lead to neurologic deficits but usually not until pain and systemic symptoms have been present for some time.

Vertebral Osteomyelitis

Vertebral osteomyelitis, the most common pyogenic infection of the axial skeleton, occurs in 2% to 19% of cases of osteomyelitis.24 Adults can present with an indolent or chronic course; the pediatric and immunocompromised groups can present more acutely. Diffuse back pain and fever are the most common symptoms, occurring in approximately 90% and 45% of patients, respectively.24 Weight loss, radicular symptoms, myelopathy, spine deformity, and meningeal irritation also occur. In some cases, neurologic deficits can be the presenting complaint.

A definitive source of infection is found in approximately 40% of cases. The most common organisms that are isolated are the gram-positive cocci, Staphylococcus aureus being the most common organism.24 Other organisms such as Escherichia coli, Pseudomonas aeruginosa, and Proteus are potential sources in parenteral drug abusers or immunocompromised patients.

Diagnosis is based on pertinent laboratory findings, including an elevated erythrocyte sedimentation rate, blood and bone cultures, and elevated white blood cell count. MRI is the gold standard for detection of osteomyelitis.25 Bone scans are useful for diagnosis, but care in interpretation is required, as other processes can have similar imaging qualities.

Epidural Abscess

Spinal epidural abscess occurs more frequently in adults. Pain is the most common presentation, but fever, leukocytosis, and neurologic compromise occur more frequently in epidural abscess than in osteomyelitis.4,6 Epidural abscesses most commonly affect the thoracic spine, followed by lumbar and cervical locations. Common etiologies include a direct extension of a preexisting osteomyelitis, hematogenous spread from a distant focus, or, less likely, trauma.4,6

As with vertebral osteomyelitis, the most prevalent species is S. aureus, followed by other staphylococcal and streptococcal species or gram-negative rods.4,6 Laboratory studies, including erythrocyte sedimentation rate and white blood cell count, are elevated in the majority of patients, and MRI is the diagnostic imaging of choice.4,6

Discitis

Spontaneous discitis is rare in the adult but occurs in 1% to 3% of surgical discectomy patients.7,8 Clinical presentation reveals back pain at the operated level, usually from 1 to 3 weeks postoperatively. The most common presentation is back pain and painful ambulation, as the lumbar spine is the most common location. Staphylococcal and streptococcal species are the most common organisms. Again, diagnosis is aided by laboratory studies, MRI, and bone scans.

Tuberculous Spondylitis

Although uncommon in developed countries, tuberculous spondylitis is the most common of the granulomatous infections that affect the axial skeleton.911 Recently, there has been a resurgence in developed countries due to the rise of HIV.12,13 Clinical presentation involves pain over the affected site, fever, malaise, and weight loss.911 In the progressive stages of disease, kyphosis results from erosive bone destruction. Epidural abscesses and paraparesis are possible late sequelae.911 Tuberculous spondylitis is usually caused by M. tuberculosis; however, other species of mycobacteria may be encountered. A positive purified protein derivative can be helpful, although false negatives can occur in the anergic patient due to advanced age, malnutrition, or immunocompromise. Diagnosis requires evaluation of urine, sputum, or a sample from a gastric specimen, subcutaneous nodule, or bone biopsy. A chest radiograph reveals no evidence of pulmonary disease in 40% to 50% of cases. MRI is superior to evaluate soft tissue involvement and the presence of abscess formation, and CT provides better bone detail.

Cryptococcus

Cryptococcus neoformans is a fungal organism that may cause infection in immunocompromised patients, mostly commonly those afflicted with AIDS. It is usually inhaled and then spreads hematogenously from a pulmonary location, with osseous involvement occurring in only 10% of cases with disseminated disease.17,18 The usual clinical presentation is swelling, pain, and decreased mobility of the affected vertebral site. Radiographs reveal dorsal vertebral body involvement and disc space sparing. Diagnosis is made via a latex agglutination test, cerebrospinal fluid (CSF) analysis, and blood cultures.

Pain Associated with Recumbency and Night Pain

Nocturnal pain and pain associated with recumbency are hallmarks of destructive lesions of the vertebral column, caused by either a skeletal metastasis or a primary bone tumor. Unfortunately, the majority of spinal column tumors are malignant. Pain is the most frequent clinical presentation, occurring in up to 85% of patients. There are correlations among age, location, incidence, and presentation. Younger patients tend to have a greater incidence of benign bone tumors, whereas those older than age 30 are more likely to have malignancy.

Benign Bone Tumors

Benign bone tumors occur more frequently in patients between ages 20 and 30, in a dorsal location and in the lumbar spine. Oosteochondroma, osteoid osteoma, and osteoblastoma are the most common benign lesions of the axial skeleton and have a lower incidence of recurrence overall compared with malignant bone tumors.

Osteochondroma

These lesions are the most common benign bone tumors, encompassing approximately 35% of all nonmalignant osseous tumors. These tumors arise from the cartilaginous end plates and are slow-growing tumors.19,20 The majority are asymptomatic lumbar spine lesions found on incidental radiographs. Symptomatic patients commonly present with dull backache, decreased motion, or, rarely, deformity. Plain radiographs demonstrate a protruding lesion with well-demarcated borders in the dorsal elements. On rare occasions, pain, neurologic deficit, or an accelerated growth pattern may be related to malignant transformation.

Giant Cell Tumor

Unlike the majority of primary bone tumors, giant cell tumors occur more commonly in patients in their 30s. The most common presentation is that of pain. However, disease advancement may result in bowel or bladder dysfunction. These aggressive tumors carry some malignant potential and a high incidence of local recurrence. They are responsible for approximately 10% of all primary benign bone tumors and affect the spinal axis in approximately 10% of all cases. These lesions may occur in conjunction with aneurysmal bone cysts (3% to 6%).23,24 They most commonly occur in the sacral region when the spinal column is involved. Plain radiographs demonstrate cortical expansion with little reactive sclerosis or periosteal reaction.23,24 Both T1- and T2-weighted MRI scans reveal homogeneous signals, whereas presurgical CT studies can better delineate the degree of vertebral bone involvement. Because of the nondistinct characteristics of giant cell tumors, radiographic investigation, coupled with intraoperative histology, is important to separate this condition from other primary bone tumors.

Aneurysmal Bone Cyst

Although responsible for only approximately 1% to 2% of all primary bone tumors, aneurysmal bone cysts affect the axial skeleton in 12% to 25% of reported cases of aneurysmal bone cysts.24 They occur more frequently in the thoracolumbar region and dorsal elements in females and patients younger than 20 years of age. Multiple vertebral involvement occurs in 40% of cases. Radiographs demonstrate a single osteolytic lesion with a thin, well-demarcated cortical rim.

Hemangioma

Hemangiomas are found in 11% of general autopsies,25,26 but symptomatic spinal hemangiomas are exceedingly rare. The most common initial symptom in the case of a solitary lesion is back pain, with or without radiation into the lower extremities.25,26 These lesions are characterized by slow growth and a female predominance.

Malignant Bone Tumors

Chondrosarcoma

This malignant cartilage-forming primary bone tumor is an uncommon spinal neoplasm. It is more common in adults, in whom it less commonly involves the spine.28 There is an even distribution of tumor involvement among cervical, thoracic, and lumbar locations.25 Chondrosarcomas may arise as a primary lesion or secondary to irradiation of lesions, including Paget disease or osteochondroma.29 The most common presentation is pain (50%) and localized swelling (30%). There is a linear relationship between degree of pain on presentation; a larger, more aggressive tumor; and decreased time of survival.30,31 Diagnosis is usually based on radiographic studies that reveal bone destruction, a soft tissue mass, and “fluffy” calcifications and pathology from resection.30,31

Osteogenic Sarcoma and Ewing Sarcoma

Both osteogenic sarcoma and Ewing sarcoma represent uncommon malignant lesions of the spinal column, with a combined incidence of less than 4% of spinal column tumors.3234 Most cases of Ewing sarcoma and primary osteogenic sarcoma (50%) present in the first 20 years of life. Secondary sarcomas arise in the fifth to sixth decades as a result of irradiated bone or a preexisting pagetoid lesion. Almost 70% of clinical presentations are accompanied by a neurologic deficit secondary to epidural compression.3234 The most common presentation of Ewing sarcoma is pain.

Chordoma

Chordomas are tumors of the axial skeleton and the skull base arising from the primitive notochord. They encompass approximately 1.4% of all skeletal sarcomas. Although chordomas are histologically low-grade lesions, they are locally invasive tumors, and metastases may occur in 5% to 43% of cases.3537 More than 50% of these lesions are located in the lumbosacral region, 35% are located in the clival and cervical area, and the remainder are spread throughout the rest of the vertebral column.37 Neurologic deficit is usually found in the form of bowel/bladder dysfunction or, less frequently, cauda equina symptoms (20%).37 Combined imaging, using MRI and CT, provides an evaluation of the tumor and its soft tissue and bony involvement.

Multiple Myeloma

Multiple myeloma and solitary plasmacytoma account for 45% of all malignant bone tumors.38 These disorders are the result of abnormal proliferation of plasma cells, which are responsible for immunoglobulin and antibody production and affect the spine in 30% to 50% of reported cases. Multiple myeloma is primarily a disease of the sixth and seventh decades of life and has a predilection for the thoracic spine (50% to 60%).

Patients present with back pain in approximately 75% of cases.38 Unlike the classic metastatic disease presentation of pain with recumbency, multiple myeloma is sometimes relieved by rest and aggravated by mechanical agitation that mimics other sciatic or neurogenic sources. Systemic complications include hyperalbuminemia, renal insufficiency, nephrolithiasis, and characteristic serum protein abnormalities. Plain radiographs and CT can be diagnostic because of the characteristic osteolytic picture without sclerotic edges that involve the ventral portion of the vertebral body and usually spare the dorsal elements.

Metastatic Disease

Metastatic disease in the form of distant foci is evident at autopsy in 40% to 85% of cases of malignancy.41 The spine is the most common site of skeletal metastasis, and at least 5% of patients with malignancies suffer from this condition.41,42 The axial skeleton is the leading site of bone metastases that are caused by hematogenous spread through the rich venous network that drains the lungs, pelvis, and thorax. Breast, lung, prostate, and thyroid malignancies account for 50% to 60% of metastatic lesions.41 Overall, epidural metastases are equally spread throughout the thoracic and lumbosacral spine, but symptomatic metastases occur most commonly in the thoracic spine. Nearly all patients initially complain of back pain, followed by weakness and ataxia. At the time of diagnosis, more than 50% of patients will have a paraparesis or bladder/bowel disturbance.41,43

Diagnostic regimens include laboratory studies demonstrating an elevated calcium level, prostate-specific antigen, or alkaline phosphatase. The ultimate diagnosis relies on radiographic studies, including plain radiographs. Bone scans are warranted for suspected occult lesions because approximately 30% to 50% of the trabeculated bone in a vertebral body must be destroyed before the lesions can be detected on plain radiography. Other radiographic modalities, including MRI and CT/myelography and positron emission tomography (PET) scans, are helpful in determining the extent of bone destruction, epidural compression, and disease spread. A metastatic workup, including both a plain chest radiograph and an enhanced abdominal/chest CT, determines the primary focus in the majority of cases. Pathologic confirmation may be made via biopsy of a primary malignant focus or via biopsy or resection of the spinal lesion.

Intradural-Extramedullary Lesions

Meningiomas, schwannomas, and neurofibromas constitute more than 50% of all neoplastic processes in the intradural-extramedullary space. Nittner’s review of 4885 adults with spinal cord tumors found schwannomas (23%) and meningiomas (22%) to be the most common lesions of the intradural-extramedullary space.45,46 Symptoms may be nocturnal and most commonly involve pain caused by root irritation. Early neurologic compromise is uncommon because of the adaptive compressibility of surrounding fat, CSF, and adjacent vascular structures. Neurologic compromise occurs when the compliance of surrounding structures is at its nadir and extradural compression is directly transmitted to the spinal cord.

More than 80% of meningiomas are located in the thoracic region, and they occur at a 4:1 ratio in women compared to men. Meningiomas can present with pain from a compressed nerve root as it exits the neural foramina. Although less common in the cervical and lumbar spine, large, slow-growing meningiomas may produce myelopathic symptoms from spinal cord compression, especially at the craniocervical junction.47 Meningiomas are the most common benign tumor at the foramen magnum.48,49 CT myelogram and MRI are the best investigative modalities.

Although both meningiomas and nerve sheath tumors are benign lesions that are usually found in thoracic dorsal sites, neurofibromas are a common finding in phakomatoses. Because neurofibromas are almost always lesions of the dorsal roots, patients commonly present with radicular symptoms.5052

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