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1 Department of Diagnostic Radiology, Rm. 406, Block K, Queen Mary Hospital, The
University of Hong Kong, 102 Pokfulam Rd., Hong Kong.
2 Department of Paediatrics, Queen Mary Hospital and Duchess of Kent Children's
Hospital, The University of Hong Kong, Hong Kong.
Received June 17, 2002;
accepted after revision July 29, 2002.
Address correspondence to P.-L. Khong.
Abstract
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SUBJECTS AND METHODS. Of 62 children consecutively seen in a neurofibromatosis 1 clinic, 53 (85.5%) were recruited for MR imaging of the whole spine. All children satisfied the clinical criteria for diagnosis of neurofibromatosis 1. Imaging findings, clinical signs and symptoms, and subsequent clinical management were reviewed.
RESULTS. The patients were 35 boys and 18 girls (age range, 11 months—18 years; mean age, 9.6 years), all of whom were asymptomatic, with no remarkable neurologic signs. Seven children (13.2%) had spinal neurofibromas: four had solitary neurofibromas (two dumbbell, one intradural, and one paraspinal tumor) and three had plexiform neurofibromas of the sacral plexus and thoracic and lumbar nerve sheaths. The incidences of scoliosis, localized cutaneous neurofibromas, and massive soft-tissue neurofibromas were 71.4%, 71.4%, and 28.6%, respectively, in the group with spinal neurofibromas (n = 7), and 30.4%, 39.1%, and 8.7%, respectively, in the group without spinal neurofibromas (n = 46). Patient clinical outcome was affected in only one patient (1.9%) in whom a solitary neurofibroma was resected. Follow-up imaging in 10 patients (mean period, 29 months) showed no evidence of tumor occurrence, progression, or recurrence.
CONCLUSION. Although benign spinal neurofibromas are not uncommon in asymptomatic children with neurofibromatosis 1, the clinical usefulness of spine surveillance with MR imaging is limited in these children, making its effectiveness questionable.
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MR images of the whole spine were obtained using a Signa 1.5-T imager (General Electric Medical Systems, Milwaukee, WI) according to the following protocol: sagittal spin-echo T1-weighted, fast spin-echo proton density—weighted, and T2-weighted axial and coronal scans at selected locations followed by contrast-enhanced sagittal scans of the whole spine and contrast-enhanced axial or coronal scans at selected locations.
MR images were reviewed for the presence of spinal tumors, including the type (solitary discrete, multiple discrete, or plexiform), site (intramedullary, intradural, extradural, dumbbell, or paraspinal), location (cervical, thoracic, lumbar, or sacral), size, and MR imaging signal characteristics. Associated MR imaging findings, including the presence of dural ectasia, lateral meningoceles, and scoliosis, were recorded. MR imaging findings were correlated with clinical signs and symptoms, in particular, scoliosis, localized cutaneous neurofibromas (nodular or polypoid lesions of the skin), and massive soft-tissue neurofibromas (massive diffuse infiltrative lesions of the soft tissue or body part, often with hyperpigmentation of the overlying epidermis). Fisher's exact test was used to detect any significant differences in the incidence of scoliosis, localized cutaneous neurofibromas, and massive soft-tissue neurofibromas in the groups of children with and without spinal tumors on MR images. A p value of less than 0.05 was considered statistically significant.
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MR Imaging Findings
Seven children (13.2%), all boys, with a mean age of 12.6 years (age range,
5-18 years) had spinal neurofibromas (Table
1). In four children, the neurofibromas were discrete, solitary,
and right-sided, with a size range of 0.5-6.5 cm. Of these, two were dumbbell
(Fig. 1), one was intradural,
and one was paraspinal (Fig.
2A,2B).
These were located in the sacral, lumbar, and upper thoracic nerves,
respectively. Three children had plexiform neurofibromas; the lesions were
widespread in two, involving the thoracic and lumbar nerve roots and the
sacral plexus (Fig.
3A,3B,3C);
and the remaining patient had a plexiform neurofibroma of the sacral plexus
that was associated with a discrete solitary neurofibroma of the T12 nerve
root. None had lesions in the cervical region. All lesions were isointense or
hypointense on T1-weighted and hyperintense on T2-weighted images relative to
the spinal cord, with hypointense centers on T2-weighted images
(Fig. 2B) and enhancement after
the administration of IV contrast material (Fig.
3A,3B,3C).
No intramedullary tumors were recorded.
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Associated spinal findings in these seven patients were scoliosis (n = 5), dural ectasia (n = 3), and lateral meningoceles (n = 1). On clinical examination, all patients had café-au-lait spots. Other findings included localized cutaneous neurofibromas (n = 5), massive soft-tissue neurofibromas (n = 2), and deep intraneural neurofibromas (axilla, mediastinal, intercostal, and parapharyngeal regions, n = 1 each).
Clinical Signs and Symptoms
None of the children was symptomatic at presentation. Except for one child
who had an absent knee reflex that did not correlate with the lesion, no
children had neurologic signs referable to spinal or peripheral nerve
disorders.
For children with spinal tumors, clinically detected scoliosis, localized cutaneous neurofibromas, and massive soft-tissue neurofibromas were found in 71.4%, 71.4%, and 28.6%, respectively; whereas the incidences of the same clinical findings in children without spinal tumors were 30.4%, 39.1%, and 8.7%, respectively. Using the Fisher's exact test, we were not able to detect any significant differences in the two groups of patients (p = 0.08, 0.22, and 0.17 respectively). The relative risks of having spinal neurofibromas in the presence of scoliosis, localized cutaneous neurofibromas, and massive soft-tissue neurofibromas were 2.4, 1.8, and 3.3, respectively.
Follow-Up
Two solitary lesions were resected: in one patient because of a tumor with
a large intradural component, and in another patient because of thigh pain
that developed during follow-up. Follow-up imaging was performed in 10
children over a mean period of 29 months. Six patients had spinal
neurofibroma, and four patients had no lesions seen on the original scans. One
patient with an upper thoracic paraspinal neurofibroma was not followed up
with MR imaging after a Harrington rod was inserted for scoliosis. He remained
asymptomatic at 7 years of clinical follow-up. No follow-up images showed
evidence of new tumor occurrence, tumor progression, or recurrence.
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In addition to spinal neurofibromas, which formed most tumors, both Egelhoff et al. [7] and Thakkar et al. [11] also detected intramedullary tumors, which were not present in our cohort. These tumors were found to be astrocytomas on histopathology. The association of intramedullary tumors with neurofibromatosis 1, although rare, has been reported, in particular the association of astrocytomas ranging from low-grade to anaplastic astrocytomas and glioblastoma multiforme [12, 13].
None of our patients was symptomatic at presentation, in agreement with the study by Egelhoff et al. [7] in which all patients with extramedullary tumors were also asymptomatic. Thakkar et al. [11] found that most spinal tumors in children (younger than 15 years old) were asymptomatic, but the frequency of tumors that were symptomatic increased with age.
Three (42.9%) of seven children in our study had plexiform spinal neurofibromas involving multiple spinal levels. It is believed that most malignant peripheral nerve sheath tumors arise from plexiform neurofibromas, although the risk of malignant transformation is low, estimated to be about 2-6% [14,15,16]. The most common age at presentation of malignant peripheral nerve sheath tumor is during adulthood, at 20-50 years old [14, 15], which may explain why we did not detect any such tumor in our young cohort. Although most plexiform neurofibromas remain benign and grow slowly, it is the experience of some authors that their natural history is unpredictable, with some tumors exhibiting little growth over extended periods and others exhibiting episodic growth punctuated by extended periods of disease stability [17]. Presently, no known predictive factors determine which lesions are likely to behave aggressively or develop malignant changes [18]. MR imaging can aid in distinguishing malignant from benign nerve sheath tumors, with the following features suggestive of malignancy: enlarging tumor, large tumor size (>5 cm), ill-defined margins, lack of a central hypointense target on T2-weighted images, and heterogeneity with central necrosis [16, 19, 20]. MR imaging is therefore useful in the follow-up of these lesions, especially because these lesions cannot be evaluated clinically. Our study is limited by the relatively short follow-up period. Nonetheless, the lack of change in the spinal tumors suggests that the lesions are nonprogressive or slow-growing.
Some authors have observed that patients with plexiform neurofibromas or localized neurofibromas of large peripheral nerves frequently have clinical findings of scoliosis [21] and multiple cutaneous neurofibromas [14]. We found an increased incidence of these disorders in patients with spinal neurofibromas compared with those without, although the differences were not statistically significant. The lack of statistical significance can be attributed to the small sample size of our cohort. Larger studies are therefore needed to determine the usefulness of these clinical findings in predicting the presence of a spinal tumor and possibly in selecting cases for MR imaging surveillance.
In our series, clinical outcome was altered in only one patient (1.9%) on the basis of MR imaging surveillance. Another patient underwent resection of the spinal tumor after developing pain during follow-up. Although surgery is recommended for symptomatic solitary [18] and plexiform [17] neurofibromas, with good prognosis and minimal morbidity, treatment for asymptomatic tumors is mostly conservative [17]. In our institution, benign, asymptomatic tumors are resected only if they are enlarging or when a risk exists of spinal cord or cauda equina compression.
In conclusion, although we found that spinal neurofibromas are not uncommon in asymptomatic children with neurofibromatosis 1, the tumors are benign and do not warrant treatment. Malignant transformation is most likely to occur only in adulthood. The clinical usefulness of MR imaging surveillance of the spine in children with neurofibromatosis 1 is limited; therefore, the effectiveness of MR imaging of these patients on a large scale is questionable.
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