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Marie-Noëlle Hébert-Blouin, Kimberly K. Amrami and Robert J. Spinner

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Marie-Noëlle Hébert-Blouin, Kimberly K. Amrami, Bernd W. Scheithauer and Robert J. Spinner

Object

In clinical practice, schwannomas are among the most common types of nerve sheath tumors. Their clinical presentation, imaging characteristics, and operative features are well known. Over the past 20 years, clinical outcomes have improved due to resection of these tumors at a fascicular level. Despite these advances, a subgroup of patients with schwannomas is associated with a disappointing neurological outcome following resection. The purpose of this study was to correlate the imaging and histological features in this group of patients with more anatomically complex forms of schwannomas.

Methods

In a retrospective review performed at their institution over a 10-year period, the authors found a subgroup of patients with complex multinodular/plexiform schwannomas affecting major peripheral nerves. Eleven patients were identified, and the clinical, imaging, and pathological features of their disease were reviewed.

Results

The clinical presentation of multinodular/plexiform schwannomas of major peripheral nerves may be similar to that of conventional schwannomas, but their imaging features, operative appearance, and outcomes differ.

Conclusions

Preoperatively and intraoperatively, the distinguishing features of multinodular/plexiform schwannomas of major peripheral nerves may be subtle and can easily go unrecognized, thus explaining the often suboptimal surgical results. Familiarity with the imaging and operative features of multinodular/plexiform schwannomas will no doubt alter treatment approaches and improve neurological function in this subgroup of patients.

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Robert J. Spinner, Bernd W. Scheithauer, Kimberly K. Amrami, Doris E. Wenger and Marie-Noëlle Hébert-Blouin

Object

Adipose lesions of nerve are rare and poorly understood. Their current classification, although not universally accepted, generally includes lipomatosis of nerve with or without localized macrodactyly, and intra- as well as extraneural lipoma. The authors believe that the spectrum of these lesions and their interrelationships are not currently appreciated. They propose an adaptation to the existing framework to illustrate the expanding spectrum of adipose lesions of nerve by considering lipomatosis and lipoma singly or in combination.

Methods

Fourteen representative cases are presented to demonstrate not only the intraneural and extraneural examples of lipomatosis and lipoma, but also their anatomical combinations.

Results

Based on the cases presented and a careful literature review, a conceptual approach to the classification of adipose lesions of nerve is generated. This approach incorporates the 2 essential lesions, lipomatosis of nerve and lipoma, in both their intra- and extraneural forms. This permits expansion to encompass combinations.

Conclusions

To press the concept that adipose tumors of nerve are a broad but interrelated spectrum of lesions, the authors propose modification of the present classification system. This approach provides an orderly platform for progress, reflects understanding of these interrelated lesions, and facilitates optimal treatment by distinguishing resectable from nonresectable components.

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Robert J. Spinner, Marie-Noëlle Hébert-Blouin, Michael G. Rock and Kimberly K. Amrami

Object

The mechanism responsible for exceptional examples of intraneural ganglia with extensive longitudinal involvement has not been understood. Such cases of intraneural cysts, seemingly remote from a joint, have been thought not to have articular connections. Decompression and attempted resection of the cyst has led to intraneural recurrence and poor neurological recovery. The purpose of this report is not only to clarify the pathogenesis of these cysts, but also to discuss their treatment based on modern concepts of intraneural ganglia.

Methods

Two examples of extreme longitudinal propagation of intraneural ganglia are presented.

Results

A patient with a moderate tibial neuropathy was found to have a tibial intraneural ganglion. Prospective interpretation of the MR imaging study demonstrated the cyst's origin from the posterior portion of the superior tibiofibular joint (STFJ), with proximal extension within the sciatic nerve to the lower buttock region. Communication between the STFJ and the cyst was confirmed with direct knee MR arthrography. The tibial intraneural cyst was treated successfully by a relatively limited exposure in the distal popliteal fossa: the cyst was decompressed, the articular branch disconnected, and the STFJ resected. Postoperatively, the patient improved neurologically and there was no evidence of recurrent cyst on postoperative MR imaging. A second patient, previously reported by another group, was reexamined 22 years after surgery. This patient had an extensive peroneal intraneural ganglion that extended into the sciatic nerve from the knee to the buttock; no joint connection or recurrent cyst had initially been described. In this patient, the authors hypothesized and established with MR imaging the presence of both: a joint connection to the anterior portion of the STFJ from the peroneal articular branch as well as recurrent cyst within the peroneal and tibial nerves.

Conclusions

This paper demonstrates that extreme intraneural cysts are not clinical outliers but represent extreme examples of other more typical intraneural cysts. They logically obey the same principles, previously described in the unified articular (synovial) theory. The degree of longitudinal extension is probably due to high intraarticular pressures within the degenerative joint of origin. The generalizability of the mechanistic principles is highlighted by the fact that these 2 cases, involving the tibial and the peroneal nerve respectively, both extended well distant (that is, to the buttock) from the STFJ via their respective articular branch of origin. These extensive intraneural cysts can be treated successfully by disconnecting the affected articular branch and by resection of the joint of origin, rather than by a more aggressive operation resecting the cyst and cyst wall.

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Marie-Noëlle Hébert-Blouin, Bahram Mokri, Alexander Y. Shin, Allen T. Bishop and Robert J. Spinner

Object

Patients with brachial plexus injury (BPI) present with a combination of motor weakness/paralysis, sensory deficits, and pain. Brachial plexus injury is generally not believed to be associated with headaches. However, CSF leaks may be associated with CSF volume–depletion (low-pressure) headaches and can occur in BPI secondary to nerve root avulsion. Only a few cases of headaches associated with BPI have been reported. It is unknown if headaches in patients with BPI occur so rarely, or if they are just unrecognized by physicians and/or patients in which the focus of attention is the affected limb. The aim of this study was to determine the prevalence of CSF volume–depletion headaches in patients with BPI.

Methods

All adult patients presenting at the Mayo brachial plexus clinic with traumatic BPI were asked to complete a questionnaire addressing the presence and quality of headaches following their injury. The patients' clinical, injury, and imaging characteristics were subsequently reviewed.

Results

Between December 2008 and July 2010, 145 patients completed the questionnaire. Twenty-two patients reported new onset headaches occurring after their BPI. Eight of these patients experienced positional headaches, suggestive of CSF volume depletion. One of the patients with orthostatic headaches was excluded because the headaches immediately followed a lumbar puncture for a myelogram. Six of the other 7 patients with positional headaches had a clear preganglionic BPI. The available imaging studies in these 6 patients revealed evidence of CSF leaks: pseudomeningoceles (n = 5), CSF tracking into soft tissues (n = 3), CSF tracking into the intraspinal compartment (n = 3), CSF tracking into the pleural space (n = 2), and low-positioned cerebellar tonsils (n = 2).

Conclusions

In this retrospective study, 15.2% of patients (22 of 145 patients) with traumatic BPI suffered from a new-onset headache. Seven of these patients (4.8%) experienced postural headaches clearly suggestive of CSF volume depletion likely secondary to a CSF leak associated with the BPI, whereas the other 15 patients (10.3%) suffered headaches that may have represented a variant of CSF depletion headaches without a postural characteristic or a headache from another cause. These data suggest that CSF volume–depletion headaches occur in a significant proportion of patients with BPI and have been underrecognized and underreported.

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Marie-Noëlle Hébert-Blouin, Bernd W. Scheithauer, Kimberly K. Amrami, Susan R. Durham and Robert J. Spinner

Object

Neuromuscular choristoma (NMC) is a rare peripheral nerve lesion in which mature skeletal muscle fibers lie within the nerve and its fascicles. Given limited follow-up, its natural history is poorly understood. The occurrence of aggressive fibromatosis in one of the authors' patients and its occurrence in reported cases suggests an etiological relationship between the 2 lesions. This study attempts to explain the association and its frequency.

Methods

All cases of NMCs seen in consultation or treated at the Mayo Clinic were identified. Demographic and clinical data were reviewed in cases with coexistent aggressive fibromatosis. Pathology and neuroimaging studies were reexamined. In addition, an extensive literature review was performed to explore the association of NMC with aggressive fibromatosis, with special attention given to pathological and imaging characteristics and the development of aggressive fibromatosis.

Results

The authors identified 10 patients with a diagnosis of NMC who were treated at the Mayo Clinic between 1992 and 2010. Four of 5 with adequate follow-up had developed a definite or suspected aggressive fibromatosis. A review of the initial pathological specimens in these cases revealed no evidence of fibromatosis, but all of the lesions exhibited accompanying hypocellular collagenous tissue. On MR images, all cases showed areas of low signal intensity, which significantly differed from muscle, nerve, and NMC components. On available serial MR imaging studies, aggressive fibromatosis seemed to originate in such lower-intensity regions. In the 18 previously reported cases of NMC, 5 patients developed recurrent masses diagnosed as either definite (2 cases) or possible (3 cases) fibromatosis. Review of the published imaging studies in these cases suggests the presence of lower intensity areas similar to those observed in the 10 patients treated at the Mayo Clinic.

Conclusions

This study confirms that the development of aggressive fibromatosis in patients with NMC has been underreported. A direct relationship between the NMC and the development of aggressive fibromatosis is suggested by pathological and neuroimaging evidence.

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Thomas J. Wilson, Marie-Noëlle Hébert-Blouin, Naveen S. Murthy, Joaquín J. García, Kimberly K. Amrami and Robert J. Spinner

OBJECTIVE

The authors have observed that a subset of patients referred for evaluation of peroneal neuropathy with “negative” findings on MRI of the knee have subtle evidence of a peroneal intraneural ganglion cyst on subsequent closer inspection. The objective of this study was to introduce the nearly invisible peroneal intraneural ganglion cyst and provide illustrative cases. The authors further wanted to identify clues to the presence of a nearly invisible cyst.

METHODS

Illustrative cases demonstrating nearly invisible peroneal intraneural ganglion cysts were retrospectively reviewed and are presented. Case history and physical examination, imaging, and intraoperative findings were reviewed for each case. The outcomes of interest were the size and configuration of peroneal intraneural ganglion cysts over time, relative to various interventions that were performed, and in relation to physical examination and electrodiagnostic findings.

RESULTS

The authors present a series of cases that highlight the dynamic nature of peroneal intraneural ganglion cysts and introduce the nearly invisible cyst as a new and emerging part of the spectrum. The cases demonstrate changes in size and morphology over time of both the intraneural and extraneural compartments of these cysts. Despite “negative” MR imaging findings, nearly invisible cysts can be identified in a subset of patients.

CONCLUSIONS

The authors demonstrate here that peroneal intraneural ganglion cysts ride a roller coaster of change in both size and morphology over time, and they describe the nearly invisible cyst as one end of the spectrum. They identified clues to the presence of a nearly invisible cyst, including deep peroneal predominant symptoms, fluctuating symptoms, denervation changes in the tibialis anterior muscle, and abnormalities of the superior tibiofibular joint, and they correlate the subtle imaging findings to the internal fascicular topography of the common peroneal nerve. The description of the nearly invisible cyst may allow for increased recognition of this pathological entity that occurs with a spectrum of findings.

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Shreehari Elangovan, Gregory M. Odegard, Duane A. Morrow, Huan Wang, Marie-Noëlle Hébert-Blouin and Robert J. Spinner

Intraneural ganglion cysts have been considered a curiosity for 2 centuries. Based on a unifying articular (synovial) theory, recent evidence has provided a logical explanation for their formation and propagation. The fundamental principle is that of a joint origin and a capsular defect through which synovial fluid escapes following the articular branch, typically into the parent nerve. A stereotypical, reproducible appearance has been characterized that suggests a shared pathogenesis. In the present report the authors will provide a mechanistic explanation that can then be mathematically tested using a preliminary model created by finite element analysis.

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Letter to the Editor

Hip- and pelvic-related intraneural ganglia

Robert J. Spinner, Marie-Noëlle Hébert-Blouin, Shota Tanaka, Kimberly K. Amrami, Karin R. Swartz, Dominic B. Fee and Makoto Sugita

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Robert J. Spinner, Marie-Noëlle Hébert-Blouin, Timothy P. Maus, John L. D. Atkinson, Nicholas M. Desy and Kimberly K. Amrami

Object

Juxtafacet cysts (JFCs) in usual locations have recently been shown to have joint connections. The pathogenesis of JFCs in unusual locations has remained obscure. The authors hypothesize that all JFCs, including atypical ones, are joint derived.

Methods

In this study the authors sought to explain the occurrence and formation of clinical outliers of spinal JFCs. In Part I, they performed an extensive literature search to identify case reports of spinal intraneural cysts that have been unappreciated despite the fact that they should occur. In Part II, they studied far-lateral (extraforaminal) cysts treated at their institution and reported in the literature. The presence of a joint connection was specifically looked for since this finding has not been widely appreciated.

Results

In Part I, 3 isolated case reports of spinal intraneural JFCs without reported joint connections were identified: 2 involving L-5 and 1, C-8. In Part II, 6 cases involving patients with far-lateral JFCs treated at the authors' institution were reviewed and all 6 had joint connections. Two of these cases had been previously published, although their joint connections were not appreciated. In 2 of the newly reported cases, arthrography confirmed a communication between the facet and the cyst. Only 1 of 5 cases in the literature had a recognized joint connection.

Conclusions

The authors believe that all JFCs are joint derived. This explanation for intraneural and extraneural JFCs in typical locations would be consistent with the unified articular (synovial) theory and the pathogenesis for intraneural and extraneural ganglion cyst formation in the limbs. Facet joints appear no different from other synovial joints occurring elsewhere. Understanding the pathogenesis of these cysts will help target treatment to the joint, improve surgical outcomes, and decrease recurrences.