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The role of imaging in isolated benign peripheral nerve tumors: A practical review for surgeons
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ScienceDirect www.sciencedirect.com Hand Surgery and Rehabilitation 35 (2016) 320–329
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The role of imaging in isolated benign peripheral nerve tumors: A practical review for surgeons Rôle de l’imagerie dans les tumeurs nerveuses périphériques bénignes isolées : étude pratique pour les chirurgiens G. Chick a,*, N. Hollevoet b, J. Victor b, S. Bianchi c a
Department of hand surgery and peripheral nerve surgery, hôpital de la Tour, 1, avenue J.D.-Maillard, 1217 Meyrin Geneva, Switzerland b Department of orthopedic surgery and traumatology, Ghent university hospital, De Pintelaan 185, 9000 Gent, Belgium c CIM SA, centre d’imagerie médicale, 40a, route de Malagnou, 1208 Geneva, Switzerland Received 17 March 2016; received in revised form 13 June 2016; accepted 1st August 2016 Available online 15 September 2016
Abstract The diagnosis of nerve tumor(s) must be suspected in all cases of tumefaction or pain on the path of a nerve exacerbated by percussion. Solitary nerve tumors are primarily schwannomas, but other rare tumors may be present such as intraneural ganglion cysts of controversial origin. Preservation of nerve continuity is the underlying goal for any surgical procedure, irrespective of the type of tumor. Therapeutic outcomes are closely linked to tumor resectability; in most patients, the resectability of the tumor, its type and benignity can be predicted based on medical imaging. Comparison with the clinical examination and case-based reasoning is crucial. Consequently, the aim of this review was to examine the role of imaging in isolated benign peripheral nerve tumors, and provide the surgeon with a practical guide for its application in predicting the nature and resectability of nerve tumors. # 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved. Keywords: Peripheral nerve tumors; Neurofibroma; Schwannoma; Intraneural mucoid pseudocyst; MR nerve imaging; Ultrasound
Résumé Le diagnostic de tumeur nerveuse doit être évoqué en cas de tuméfaction ou de douleur sur le trajet d’un nerf que la percussion réveille. Les tumeurs nerveuses isolées sont en majorité des schwannomes ; les autres tumeurs sont beaucoup plus rares et d’une grande diversité histologique, comprenant les pseudo-kystes mucoïdes des nerfs dont l’origine est controversée. Quel que soit le type de tumeur, le traitement chirurgical vise à respecter la continuité nerveuse. Le pronostic est étroitement lié au caractère extirpable de la lésion. L’analyse radiologique permet, chez la plupart des patients, de prévoir l’extirpabilité, la nature et la bénignité des tumeurs. La confrontation avec l’examen clinique et la casuistique est essentielle. Le but de cette revue était d’analyser le rôle de l’imagerie en cas de tumeur nerveuse périphérique isolée et de faire une synthèse des critères cliniques et paracliniques qui permettront au chirurgien de prévoir au mieux le caractère extirpable et la nature des lésions. # 2016 SFCM. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Tumeurs des nerfs périphériques ; Neurofibrome ; Schwannome ; Pseudokyste mucoïde des nerfs ; IRM ; Échographie
1. Introduction * Corresponding author. E-mail addresses: [email protected] (G. Chick), [email protected] (N. Hollevoet), [email protected] (J. Victor), [email protected] (S. Bianchi).
Benign tumors of the peripheral nerves (BTPN) are rare tumors that can occur either as isolated lesions [1] or in multiple forms [2], as in neurofibromatoses (not included in this review).
http://dx.doi.org/10.1016/j.hansur.2016.08.001 2468-1229/# 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved.
G. Chick et al. / Hand Surgery and Rehabilitation 35 (2016) 320–329
Surgical treatment and prognosis vary greatly depending on whether the tumor is resectable, with the ultimate goal of the surgical procedure being the preservation of nerve continuity. Consequently, the aim of this review was to examine the role of imaging in isolated benign peripheral nerve tumors, and to provide the surgeon with a practical guide for its application in predicting the nature and resectability of nerve tumors. The general characteristics of benign nerve tumors (including patient presentation and radiological aspect) and specific features of the various tumor types are successively reviewed. 2. General characteristics of benign tumors of peripheral nerves
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discovery is made during surgery or imaging for nerve entrapment syndrome in young adults. More rarely, the diagnosis is made secondary to nerve resection performed erroneously for a diagnosis of lymphadenopathy (especially in the supraclavicular fossa), synovial cyst or resectable tumor [7]. 4. Radiological characteristics of BTPN Ultrasound (US) and magnetic resonance imaging (MRI) [8,9] are the reference imaging modalities for the diagnosis of BTPN. Computed tomography (CT) is rarely performed because of its low resolution for soft tissues. 4.1. US vs. MRI
BTPN represent approximately 1% of all soft tissue tumors [1]. While more frequent in the upper limb and mostly affecting large nerve trunks [3], ultimately any nerve can be affected. Eighty percent of BTPN are schwannomas [1,4]. BTPNs are rooted in either the nerve tissue or the non-neural elements of the nerve. From a practical and prognostic perspective, resectable tumors should be distinguished from non-resectable ones (Table 1). Essentially, resectable tumors grow eccentrically from the nerve, pushing back the fascicle groups without penetrating the perineurium and can be enucleated without disrupting nerve continuity. On the other hand, nonresectable tumors infiltrate all constituent elements of the nerve, with nerve fiber damage always occurring upon complete removal. Consequently, an epineurotomy for decompression is recommended in case of nerve compression symptoms [1,5]. 3. Patient presentation Most patients present with swelling over the course of a superficial nerve or, more rarely, localized pain and/or paresthesia revealed by percussion if a deeper nerve is involved [5,6]. BTPNs are solely responsible for neurological deficits by compressive intraneural damage (non-resectable tumors), development in a narrow anatomical groove or development spanning many years (resectable tumors). In some cases, its
As a general rule, peripheral nerves are more visible when surrounded by tissues of a different echostructure. Peripheral nerves appear as tubular structures made of hypo-echoic nerve fascicles embedded in a hyperechoic connective tissue corresponding to the epineurium. Longitudinally, US images present a fascicular pattern, and transversely, fascicles appear rounded or oval in shape, giving the nerve the typical honeycomb appearance [10,11]. US diagnosis of a nerve tumor is based on the existence of a mass in continuity with the nerve at its proximal and distal poles [12]. While US eliminates the vast majority of false tumor lesions and allows for differentiation between lymphadenopathy, neuroma or liquid tumor (hematoma, abscess or thrombosed aneurysm), it is more operator-dependent than MRI with nerve lesions rarely being specific. Color Doppler ultrasound allows an accurate assessment of the presence of intralesional flow and helps in differentiating solid and cystic lesions [12]. Its dynamic method of study enables the physician to analyze the entire nerve course and look for other remote tumor [10]. USguided pressure through the transducer on the mass can reproduce local pain and peripheral paresthesia (the so-called ‘‘ultrasonographic Tinel sign’’). This can be very helpful when assessing small peripheral lesions. But ultimately, US cannot replace MRI for determining the topography, the exact extent of tumor formation or the presence of invasion [13]. The boundary between the tumor and the nerve is sometimes difficult to
Table 1 Classification and origin of main single benign peripheral nerve tumors. Benign peripheral neural sheath tumors (PNSTs)
Peripheral non-neural sheath tumors
Schwannomaa
Intraneural hemangioma
b
Neurinoma Neurilemmomab
Neurofibroma
b
Perineural hemangioma Schwann sheath hemangiomab Intrinsic hemangioma of the peripheral nerveb (Extrafascicular intraneural hemangioma)a
Fibrolipomatous hamartoma b
Fatty infiltration Lipofibromab Intraneural lipofibromab
Intraneural lipomaa
Intraneural ganglion cyst Intraneural mucoid pseudocystb Nerve sheath ganglionb Intraneural synovial cystb
Neuro-fibrolipomab Fibro-fatty proliferationb
Traumatic neuromas and pseudoneuromas (following nerve injury) are excluded. Desmoid tumors and neuromuscular choristoma (benign triton tumor) of controversial origin are excluded. a Resectable tumors. b Equivalent nerve tumor terms.
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Table 2 Similarities and differences between isolated benign peripheral sheath tumors (general and MRI features).
Predominant age (years) Sex ratio (male/female) Location (most common) Macroscopic appearance
Condition of parent nerve T1-weighted signal T2-weighted signal
Enhancement intensity
Particularities Cystic and solid changes Target sign Fascicular sign Split fat sign
Schwannoma
Solitary neurofibroma
20–50 1 Supraclavicular brachial plexus Encapsulated, globular, pale yellow Eccentric ++
20–30 8.7 Supraclavicular brachial plexus Non-encapsulated, fusiform
Hypo- or iso-intense/muscle Hyperintense/fat
Diffuse ++ Predominantly peripheral ++ + ++ ++
Nerve cylindrical expansion Iso-intense/muscle Peripheral hyperintensity (target sign +++) Variable, moderate Central ++
+++ +? +
determine because the nerve may be distended and stretched over the mass. The neural origin of a mass from a small nerve (single hypo-echoic fascicle) is also very difficult to determine, particularly in superficial lesions [12]. Nevertheless, the use of high-frequency transducers has led to better detection of smaller nerves. MRI evaluation consists of different sequences (e.g., T1, T2, FAT SAT, IV Gadolinium), with images in the same plane (usually axial) supplemented by at least one other sequence in an orthogonal (sagittal, coronal) plane. The use of coils dedicated to the anatomic region of interest improves the homogeneity of the signal and spatial resolution. Positioning the patient and area for exploration at the magnet center is essential for ensuring high quality images. These can be further improved by contrast enhancement, 3D or 4D images, tractography or by magnetic resonance angiography (MRA), depending on the type of lesion. Gadolinium-enhanced images
must always be obtained to provide conclusive differentiation between a cystic and a solid lesion. A normal nerve has intermediate signal intensity, identical to muscle on T1 and T2 sequences. It is best viewed on T1 sequences in fatty layers or on T2-weighted fast SE and T2 fatsuppressed sequences, where it appears hyperintense compared to muscle [14]. There is no nerve enhancement after contrast injection. When dealing with a mass located in the region of a nerve, MRI allows a diagnosis in 75% of cases. Coronal and sagittal images provide individualization of the nerve’s entry and exit of the tumor [15]. Some signs (target sign, fascicle appearance, split fat sign) are especially suggestive of the benign nature of the lesion [12,13,16] and the combination of sequences and images after enhancement by contrast medium may reveal the nature of the tumor (Tables 2 and 3) [8,17]. Bone overlays do not interfere with scanning, unlike in US. In patients with signs of neurological deficits, it helps to assess the state of the nerve and the impact of denervation on the affected muscles [17,18]. MRI makes it possible to differentiate between a soft tissue tumor compressing the nerve, lymphadenopathy, thrombosed hemangioma, saccular aneurysm or neuroma. However, small movements can lead to artifacts and hinder interpretation of the images (need for complete immobilization during image acquisition). Furthermore, in contrast to US, MRI does not allow dynamic examination, allowing only a focused examination without the possibility of a panoramic study. 4.2. Computed tomography Computed tomography (CT) only shows the nerve as a nonspecific structure of intermediate density; it is a complementary diagnostic tool, except in very specific regions of the brachial plexus. Like standard radiographs, it may be helpful in visualizing an underlying bone abnormality. 5. Radiological characteristics by tumor type 5.1. Schwannomas 5.1.1. General considerations Schwannomas are observed at all ages, but most often between 20 and 50 years without a sex predominance [5,6,19].
Table 3 Similarities and differences between various types of isolated benign peripheral non-neural sheath tumors (general and MRI features). Intraneural lipoma
Fibrolipomatous hamartoma
Intraneural hemangioma
Intraneural ganglion cyst
Predominant age (years) Sex ratio (male/female) Location (most common) Macroscopic appearance Condition of parent nerve T1-weighted signal
40–60 Female > Male Median n Encapsulated, oval, yellow
10–20 Female +++ Median n Non-encapsulated locular
40 Male ++ Common peroneal n Translucent mass encapsulated
Heterogeneous signal
Iso- or hypo-intense/muscle
T2-weighted signal
High (similar to fat)
< 30 1 Median n (exclusive) Fusiform Nerve enlargement Coaxial cable-like (coronal) Spaghetti-like (sagittal) Coaxial cable-like (coronal) Spaghetti-like (sagittal)
Hyperintense
Hyperintense Muscle denervation
Enhancement intensity Particularities
No enhancement Low signal (STIR)
n: nerve.
High (similar to fat)
Slowly hyperintense enhancement
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Fig. 1. Isolated benign peripheral sheath tumors (ulnar nerve at the wrist): schwannoma: macroscopic appearance (A). Ultrasound: isolated globoid mass located along the nerve and eccentric to the nerve axis with homogeneously hypo-echoic structure with posterior acoustic enhancement (B). MRI: coronal FS T1-weighted following IV contrast: round mass with central enhancement, in direct continuity with nerve at its proximal and distal poles (C). S: schwannoma. White arrowheads: ulnar nerve. FS: fat suppression. Solitary neurofibroma: intraoperative view (D). Sagittal US imaging shows a fusiform iso-echogenic lesion (NF) with the nerve (white arrowheads) centrally entering and exiting the mass. Note again the centrally located nerve entrance and exit (E). MRI: sagittal proton density with fatsuppressed weighted image (F). NF: neurofibroma.
They are most common in the upper limbs (70%) [5,15,20], and are mainly located proximally to the brachial plexus (44%) and on peripheral nerve trunks (26%) [5,20]. In the lower limbs, the trunk of the sciatic nerve or the common peroneal nerve are most frequently affected [5]. Their macroscopic appearance is quite discernible, with an encapsulated, generally rounded, pale yellow tumor, located off-center in continuity with the nerve (Fig. 1A). Size varies depending on location, although most schwannomas are less than 2.5 cm in diameter [3]. 5.1.2. Radiological investigations No image is specific of schwannoma [15,18,21–23]; the noncentered nature of the tumor relative to the nerve, which is usually assessed on axial images, appears to be the most defining feature of a schwannomatous nerve tumor [24] (Table 2). 5.1.3. US Most schwannomas have the shape of a globoid mass with clearly defined margins, off-centered along the nerve [10], with a homogeneous or a more or less heterogeneous hypo-echoic
structure, with or without posterior contrast enhancement, depending on their cystic or solid internal appearance [12,18] (Fig. 1B). Schwannomas are most often hypervascular on color Doppler, followed by neurofibromas [13]. Although internal flow signals in a BTPN suggest a schwannoma, US does not allow definitive differentiation from a neurofibroma [13]. 5.1.4. MRI A schwannoma appears as an eccentric globular mass located on a neurovascular bundle when a large-caliber nerve is affected. The signal of the mass is hypo-intense or iso-intense on T1-weighted images and hyperintense, heterogeneous or not, on T2-weighted images, depending on intrinsic changes in the tumor (Fig. 1C). Sometimes a hypo-intense pseudocapsule corresponding to the epineurium is visible. It appears well defined, readily surrounded by a halo of fat (split fat sign) [19]. In some cases, the appearance of a target corresponds to a central hypo-intensity (fibrous tissue region) on T2-weighted images surrounded by a peripheral hyperintensity (myxoid region) [17,25]. In this case, gadolinium injection enhances the signal [22]. The fascicular sign corresponds to multiple small
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ring-like structures (with peripheral higher signal intensity) on either T2- or proton density-weighted MR imaging [16,17,22,26]. Schwannomas are more commonly associated with a fascicular [22] and split fat sign [18] than neurofibromas; a target sign is more common in neurofibroma (Table 2). 5.1.5. CT Most schwannomas appear as a round or oval mass that is off-center relative to the nerve, hypodense (or more rarely isodense) compared to the muscle, and homogeneously or heterogeneously enhanced after injection of contrast medium, depending on the predominant cellular components and the cystic and/or hemorrhagic changes [25], giving it the target sign [17].
or oval (spindle neuroma) in the axis of a severed or damaged nerve [16,19] and is dissociated from the nerve fascicles. The echostructure is sometimes mixed, with characteristic sensitivity to probe passage. On MRI, the neuroma has the same hypo-intense signal intensity as the muscle on T1-weighted images, but is hyperintense compared to the muscle on T2weighted images; enhanced again after contrast [16]. Plexiform neurofibroma is seen exclusively in Von Recklinghausen neurofibromatosis. MRI shows a convoluted mass composed of countless neurofibromas developed from the nerve fascicles in the affected nerve trunk, typically on a long portion with side branches [29], creating the appearance of a ‘‘bag of worms’’ [26]. 5.3. Intraneural lipoma
5.2. Solitary neurofibroma 5.2.1. General considerations Solitary neurofibromas represent 10% of isolated nerve tumors, usually affecting young adults [6] between 20 and 30 years old, with a male/female ratio of 8.7 [5]. They are often located proximally (supraclavicular plexus 55%, major nerve trunks 45%) in the upper limbs [5,27], while in the lower limbs, pelvic plexus and sciatic nerve involvement is common [5]. It is a non-encapsulated tumor (always demarcated) growing inside the nerve that encases each fascicle and stretches it, leading to the appearance of an irregular cylindrical expansion of the nerve (Fig. 1D). 5.2.2. US Neurofibromas, which are intimately mingled with the nerve tissue, are characterized by a fusiform swelling (not globoid), with nerve fibers entering and exiting the ends of the swollen area (Fig. 1E). They are well-defined masses with sharp borders that usually have a hyp-oechoic appearance. Contrary to schwannomas, they do not contain anechoic areas. Internal calcifications are rare. Unlike schwannomas, ultrasound imaging in the axial plane does not result in visible nerve fascicles. Neurofibromas are less hypervascularized on color Doppler than schwannomas [12,26]. 5.2.3. MRI Neurofibromas appear elongated and usually have signal intensity identical to that of muscle on T1 sequences. Enhancement is usually moderate and variable after contrast medium injection [28] (Fig. 1F), while the target sign in T2 (initially described as pathognomonic) is often non-specific [17,26,28] (Table 2). 5.2.4. CT The neurofibroma is hypodense. Sometimes a target is present (central hyperdensity, peripheral hypodensity). 5.2.5. Differential diagnosis The differential diagnosis of solitary neurofibroma includes schwannoma, neuroma and plexiform neurofibroma. The neuroma appears hypo-echoic, rounded (terminal neuroma)
5.3.1. General considerations Intraneural lipomas are extremely rare with just 15 cases reported in the literature [1,5,30,31]. Prior to histological identification, these lipomas were often mistaken for fibrolipomatous hamartoma [31]. Intraneural lipomas develop predominantly in female patients between the ages of 40 and 60 years. Their slow growth explains the high tolerance rate. Lesions are typically located on the median nerve (causing clinical signs of carpal tunnel) but have been reported on other nerves as well [1,5,7,31]. Intraneural lipomas appear as an encapsulated tumor [1,31,32], usually > 5 cm in diameter with nerve fibers running along its surface (Fig. 2A). Thus, complete excision without nerve damage is possible [32]. Some intraneural lipomas seem to originate in individual nerve fascicles and can cause a mass effect on the affected nerve. Histological examination reveals that these tumors consist exclusively of adipose tissue without neural elements [31,32]. 5.3.2. US Intraneural lipomas appear as hyperechoic oval masses with well-defined borders. Color Doppler typically shows no blood flow signals inside the mass. 5.3.3. MRI The MRI appearance is similar to that of other locations with a soft tissue tumor that is clearly defined, having the same signal characteristics as subcutaneous fat in all sequences. On T1 and T2 sequences, the signal intensity is notably high, while on T2-weighted sequences obtained with fat saturation, the signal intensity is low with the nerve fascicles around the viewable mass (Fig. 2B) [32]. No enhancement is observed after contrast injection (Table 3) [7,32]. 5.3.4. Differential diagnosis The differential diagnosis for intraneural lipoma includes extrinsic lipoma compressing a nerve, fibrolipomatous hamartoma or a well-differentiated liposarcoma. In case of liposarcoma, some suspicious signs are heterogeneous appearance (nodules or non-fatty areas), poorly defined margins, size larger than 5 cm or atypia (calcifications, septa thickening by more than 2 mm and bleeding). Importantly, MRI with
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Fig. 2. Isolated benign peripheral non-neural sheath tumors. Intraneural lipoma: macroscopic aspect: well-encapsulated intraneural lipoma that spread the nerve fibers (digital nerve) (A). MRI: sagittal SE T1-weighted image (left) of the wrist showing a mass that has the same signal intensity as subcutaneous fat within the median nerve. Sagittal SE T2-weighted image (right) with fat suppression at the same level shows complete saturation of signal within the mass, confirming that it is fat (B). Note the fascicles of the median nerve draped around the superior aspect of the mass (Reproduced by kind permission of Elsevier from Amrami et al. [18], L: intraneural lipoma). Intraneural extrafascicular hemangioma of the median nerve (CDE): macroscopic appearance (C) and after removal (D). H: hemangioma; blue arrowhead: flexor carpi radialis tendon; white arrowhead: median nerve. MRI: axial SE T1-weighted image IV: high signal intensity with moderate enhancement after intravenous contrast administration as well as tubular structures suggesting feeding or draining vessels (blue arrowhead: median nerve) (E).
gadolinium injection is necessary to search for a fibrous component (fibrolipoma) or sarcomatous transformation [33]. 5.4. Intraneural hemangioma 5.4.1. General considerations Unlike vascular malformations, which are the result of abnormal vasculogenesis with normal endothelial renewal, hemangiomas are tumors involving cell proliferation [34]. Intraneural hemangioma are extremely rare, almost exclusively observed in females often during the first decade of life [1,35– 37], with median nerve most commonly affected [35–37]. An intraneural hemangioma has the same characteristics as the conventional hemangioma, from which it is distinguished only by its location. The intraneural hemangioma can have an extrafascicular (Fig. 2C and D), intrafascicular or mixed development [36]. Depending on the degree of intrafascicular invasion, excision is not possible without sacrificing the nerve [35,36]. Extrafascicular forms are resectable tumors (Table 1). 5.4.2. US Hemangiomas can always be characterized by US, especially if phleboliths (which appear as hyperechoic small structures with posterior shadowing) are present on standard radiographs. A hemangioma appears as a tissue mass with mixed echogenicity with poorly defined borders. The mass may show an arterial (fast flow) or a weak venous Doppler signal (slow flow). 5.4.3. MRI MRI (Fig. 2E) shows an infiltrating, poorly defined mass with heterogeneous signal intensity, and dilated and serpiginous vascular structures that may contain phleboliths, enhancing
very slowly after contrast medium injection. Fatty spots are scattered throughout the tumor in T1; this can sometimes determine whether the lesion is intra- or extraneural. T2weighted images have the characteristic appearance of hyperintense clusters [38] (Table 3). 5.4.4. Magnetic resonance angiography (MRA) MRA is a non-invasive 3D imaging technique that allows vascular structures to be delineated [39]. MRA can objectify the afferent and efferent vessels of the hemangioma [40]. Complementarily to MRI and color Doppler ultrasound, MRA is useful in assessing the extension of the tumor process [39,41]. The evolution of 4D-MRA and ‘‘time-resolved’’ (TRMRA/dynamic MRA) should be considered as a valuable alternative to conventional MRA in the imaging of vascular pathologies [42]. 5.4.5. Differential diagnosis The differential diagnosis includes extraneural hemangioma, thrombosed aneurysm, hypervascularized soft tissue tumor or arteriovenous malformation. In a thrombosed aneurysm, there is a heterogeneous hyperechoic area around the aneurysm (thrombus) with a pulsatile back-and-forth flow revealed by a color Doppler. In an arteriovenous malformation, there is no tissue component and presence of an early venous return. 5.5. Fibrolipomatous hamartoma 5.5.1. General considerations Fibrolipomatous hamartoma of the nerve has been described using equivalent terms such as fatty infiltration, lipofibroma, fibro-fatty proliferation, and intraneural lipofibroma. The
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fibrolipomatous hamartoma is a rare tumor, probably of congenital origin [43]. Approximately 100 cases have been reported in the literature [44,45], mostly involving young adults under the age of 30, with no gender imbalance [44,46]. The preferred sites are the median nerve and its side branches. It presents as soft swelling of the distal forearm [46], wrist or palm existing since childhood, often asymptomatic, sometimes bilobated on either side of the carpal tunnel, and associated with macrodactyly in 30% of cases [44,46]. The mass grows slowly, causing median nerve compression signs. The affected nerve appears enlarged due to fibro-fatty endoneural, perineural and epineural infiltration [32], which can cause the nerve to reach up to three times its normal size (Fig. 3A and B). 5.5.2. Standard X-rays X-rays show edema of the soft tissues in the affected area with or without macrodactyly. There may be bone hypertrophy with signs of osteoarthritis [46]. 5.5.3. US US reveals a fusiform mass with longitudinally distributed nerve fascicles marked by hyper- and hypo-echoic bands [26,46]. As described by Toms et al. [47], these tumors appear as ‘‘characteristic hypo-echoic coaxial cabling encased by an echogenic substratum’’ (Fig. 3C). 5.5.4. MRI The MRI appearance is pathognomonic [18,46,48,49], with hypertrophy of the median nerve (up to 1.6 cm2 in caliber), with round, oval or multilocular shape, which has a hyperintense signal similar to fat, with individuation of hypo-intense longitudinal bands along the axis of the nerve corresponding to the fascicles. In T1 and T2 sections, this contrast gives a coaxial ‘‘cable-like’’ appearance on axial images and
‘‘spaghetti-like’’ appearance on coronal and sagittal images (Fig. 3D and E) [26,32,46,48]. Fine hypo-intense septa inside the fat tissue separate the nerve fascicles (Lotus sign): these correspond to the typical feature of perineurium thickening (Table 3). 5.5.5. CT The CT scan shows a mass inside the carpal tunnel causing the flexor retinaculum and tendons to shift over. The dense part of the mass has fibroblastic elements [46]. 5.6. Intraneural ganglion cyst 5.6.1. General considerations Intraneural ganglion cysts are characterized by infiltration of the nerve by a mucoid substance, thereby forming an intraneural tumor. The hypothesis of a joint origin from a joint nerve branch is the most commonly accepted one [50–52]. The tumor is usually revealed by a sharp pain or symptoms of nerve compression, followed by neurological deficit in the corresponding nerve segment, as the pain fades. The time between the first symptoms and diagnosis is relatively short (3 to 7.4 months) [53]. This is explained by the rapid growth of the pseudocyst and the presence of a neurological deficit that often alarms the patient. While a short series has been published, most cases are isolated, affecting men in their 40s [50,51,53,54]. The lesions affect mostly mixed nerves. The preferential site is the common peroneal nerve in the fibular neck [53]. Other sites have the particular characteristic of being near a joint or a narrow anatomical groove. The ulnar nerve in the elbow is the most common site in the upper limb [53]. Intraneural ganglion cysts appear as a single or multiple translucent mass encapsulated in the nerve trunk. The nerve fascicles on the outer surface are often dilacerated and integrated into the wall (Fig. 4A).
Fig. 3. Fibrolipomatous hamartoma of the median nerve at the wrist: macroscopic appearance (A) and after epineurotomy (B). Ultrasound appearance with color Doppler (C): hypo-echoic thickened axonal bundles interspersed in echogenic fatty tissue with no intralesional blood flow. The median nerve is outlined in this axial view, which demonstrates the coaxial ‘‘cable-like’’ appearance. MRI axial T1-weighted image of wrist shows thickened hypodense nerve fascicles surrounded by hyperintense fibro-adipose tissue giving it a coaxial ‘‘cable-like’’ appearance (white arrowhead) (D). MRI Sagittal T1 fat saturation IV weighted image shows ‘‘spaghetti-like’’ appearance of the lesion (white arrowhead) (E).
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Fig. 4. Intraneural mucoid pseudocyst (common peroneal nerve): Intraoperative view (A): intraneural mucoid cyst of the common peroneal nerve (green arrowhead) with peroneal intraneural ganglion arising from the superior tibiofibular joint and extending along the articular branch (blue arrowhead) to the common peroneal nerve. MRI (B): sagittal T2-weighted image shows cyst arising from the superior tibiofibular joint and extending to the common peroneal nerve and its branches (black arrowheads). Delayed CT arthrography (C): curved multiplanar reformatted CT image shows a long, thin pedicle between the cysts at the anterior aspect of the tibiofibular joint and the intraneural cyst (white arrow) (courtesy of J. Malghem, MD).
5.6.2. Electromyography (EMG) EMG simply confirms potential nerve damage and specifies the compression site. 5.6.3. US US can locate the delimited lesion and its fluid nature (anechoic or quasi-anechoic mass, sometimes multilocular with posterior enhancement of the signal). However, the resolution is often insufficient to clarify the relationship between the cyst and neighboring joint; in general, US cannot distinguish the communicating pedicle of the cyst, which is long and thin [54]. 5.6.4. MRI MRI confirmed the tumor’s fluid nature, its location and extension. The signal is iso-intense or hypo-intense relative to the muscle on T1-weighted images. On T2-weighted images, the signal is intense, with well-defined and sometimes multilocular rims. Only the signal of thin walls is enhanced rapidly upon injection of intravenous contrast agent. The nerve fascicles shift to the margins of the intravenous cyst in a crescentic intraneural fashion, giving a ‘‘signet ring’’ appearance. The nerve itself may show a moderate enhancement and hyperintensity in T2 images related to the mass effect. The sagittal images indicate the state of the nerve, which is laminated and thinned. The appearance of the pedicle may vary, depending on its liquid contents: it is only visible in one in four cases, when it may be identified on the joint CT scan [54]. The use of 3D reconstructed images (Fig. 4B) can facilitate its detection [51,52]. In the event of motor or previous damage, the MRI can reveal signal abnormalities in the affected muscles, which may have visible signs of denervation such as muscle edema, adipose involution and muscle atrophy. MRI can confirm recurrence, and may be useful for long term monitoring (Table 3). 5.6.5. CT CT objectifies the content of the cyst, with a density slightly lower than that of the muscles, and a well-defined, sometimes multilobular appearance. The wall of the cyst can be viewed using intravenous iodinated contrast medium.
5.6.6. CT arthrography CT arthrography is not the method of choice for diagnosing mucoid cysts. However, it is an efficient method for proving the existence of a pedicle communicating with the joint, which is of surgical interest [50,54]. CT arthrography images must be obtained several hours after the intra-articular injection of the contrast medium (Fig. 4C), due to slow diffusion of the contrast in the cystic gelatinous material [52,54,55]. 5.6.7. Differential diagnosis The differential diagnosis for intraneural ganglion cyst includes other peripheral nerve tumors (cystic schwannomas), malignant tumor with myxoid contents, juxta-articular synovial cyst compressing the nerve, hematoma, aneurysm of the popliteal artery, intramuscular or juxta-articular myxoma or entrapment syndrome. 6. Future directions Imaging sensitivity and specificity have increased greatly with the help of metabolic positron emission tomography (PET), and will continue to increase in the future with functional magnetic resonance spectroscopy and diffusion tensor imaging. The information provided by contrast image diffusion (tractography imaging) will be crucial for obtaining data on the integrity of the nerves in both benign and malignant lesions of the peripheral nerves. Tractography is a new MRI technique that allows assessment of the internal microarchitecture of peripheral nerves. BTPN and entrapment neuropathies have been evaluated using tractography; however, this technique is no longer used during routine evaluation of peripheral tumors because of a lack of harmonization of the protocols and data post-processing methods [56]. Diagnostic methods are moving towards a combination of metabolic, functional and anatomical images, to assist in the differentiation of diverse clinical entities [21]. 7. Conclusion Both US and MRI of large-caliber nerves can confirm the neural nature of a tumor. While US is the primary imaging modality, due to its ease of use, low price and accessibility, MRI
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remains the gold standard as it is able – in the vast majority of cases – to identify the type of tumor and importantly, determine its resectability. While imaging is crucial in the diagnostic work up of patients suspected of or presenting with benign tumors of peripheral nerves, it is essential that clinicians understand that imaging is just one tool in their arsenal. A robust clinical examination is indispensable, with close cooperation between the surgeon, radiologist and histologist being essential. But even after a robust clinical examination combined with extensive secondary imaging, the tumor’s resectability is sometimes only known following an epineurotomy. Disclosure of interest The authors declare that they have no competing interest. Acknowledgements We are grateful to Mathew Wilson, PhD, for reviewing the English version of this manuscript. References [1] Chick G, Alnot JY, Silbermann-Hoffman O. Benign solitary tumors of the peripheral nerves. Rev Chir Orthop Reparatrice Appar Mot 2000;86: 825–34. [2] Chick G, Alnot JY, Silbermann-Hoffman O. Multiple peripheral nerve tumors: update and review of the literature. Chir Main 2003;22:131–7. [3] Forthman CL, Blazar PE. Nerve tumors of the hand and upper extremity. Hand Clin 2004;20:233–42. [4] Sandberg K, Nilsson J, Søe Nielsen N, Dahlin LB. Tumours of peripheral nerves in the upper extremity: a 22-year epidemiological study. Scand J Plast Reconstr Surg Hand Surg 2009;43:43–9. [5] Kim DH, Murovic JA, Tiel RL, Kline DG. Operative outcomes of 546 Louisiana State University Health Sciences Center peripheral nerve tumors. Neurosurg Clin N Am 2004;15:177–92. [6] Kehoe NJ, Reid RP, Semple JC. Solitary benign peripheral-nerve tumours. Review of 32 years’ experience. J Bone Joint Surg Br 1995;77:497–500. [7] Matsuo T, Sugita T, Shimose S, Kubo T, Yasunaga Y, Ochi M. Intraneural lipoma of the posterior interosseous nerve. J Hand Surg [Am] 2007;32:1530–2. [8] Dorsi MJ, Belzberg AJ. Peripheral nerve tumors of the extremities. In: Schmidek HH, Roberts DW, editors. Schmidek and Sweet’s operative in neurosurgical techniques. 6th ed., Philadelphia: Elsevier; 2012. p. 2319–27. [9] Hems TE, Burge PD, Wilson DJ. The role of magnetic resonance imaging in the management of peripheral nerve tumours. J Hand Surg [Br] 1997;22:57–60. [10] Bianchi S. Ultrasound of the peripheral nerves. Joint Bone Spine 2008;75:643–9. [11] Martinoli C, Bianchi S, Cohen M, Graif M. Ultrasound of peripheral nerves. J Radiol 2005;86:1869–78. [12] Valle M, Zamorani MP. Nerve and blood vessels. In: Bianchi S, Martinelli C, editors. Ultrasound of the musculoskeletal system. Berlin: SpringerVerlag; 2007. p. 97–134. [13] Garcia J, Bianchi S. Diagnostic imaging of tumors of the hand and wrist. Eur Radiol 2001;11:1470–82. [14] Grant GA, Britz GW, Goodkin R, Jarvik JG, Maravilla K, Kliot M. The utility of magnetic resonance imaging in evaluating peripheral nerve disorders. Muscle Nerve 2002;25:314–31. [15] Nilsson J, Sandberg K, Søe Nielsen N, Dahlin LB. Magnetic resonance imaging of peripheral nerve tumours in the upper extremity. Scand J Plast Reconstr Surg Hand Surg 2009;43:153–9. [16] Abreu E, Aubert S, Wavreille G, Gheno R, Canella C, Cotten A. Peripheral tumor and tumor-like neurogenic lesions. Eur J Radiol 2013;82:38–50.
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G. Chick et al. / Hand Surgery and Rehabilitation 35 (2016) 320–329 [45] Arora R, Arora AJ. Imaging features on sonography and MRI in a case of lipofibromatous hamartoma of the median nerve. Quant Imaging Med Surg 2014;4:207–9. [46] Tahiri Y, Xu L, Kanevsky J, Luc M. Lipofibromatous hamartoma of the median nerve: a comprehensive review and systematic approach to evaluation, diagnosis, and treatment. J Hand Surg [Am] 2013;38:2055–67. [47] Toms AP, Anastakis D, Bleakney RR, Marshall TJ. Lipofibromatous hamartoma of the upper extremity: a review of the radiologic findings for 15 patients. AJR Am J Roentgenol 2006;186:805–11. [48] Marom EM, Helms CA. Fibrolipomatous hamartoma: pathognomonic on MR imaging. Skeletal Radiol 1999;28:260–4. [49] Nardella D, Sohawon S, Carlier A. Lipofibromatous hamartoma of the median nerve. Three case reports. J Plast Reconstr Aesthetic Surg 2009;62:e314–7. [50] Spinner RJ, Desy NM, Rock MG, Amrami KK. Peroneal intraneural ganglia. Part I. Techniques for successful diagnosis and treatment. Neurosurg Focus 2007;22:E16.
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Recent advance
The role of imaging in isolated benign peripheral nerve tumors: A practical review for surgeons Rôle de l’imagerie dans les tumeurs nerveuses périphériques bénignes isolées : étude pratique pour les chirurgiens G. Chick a,*, N. Hollevoet b, J. Victor b, S. Bianchi c a
Department of hand surgery and peripheral nerve surgery, hôpital de la Tour, 1, avenue J.D.-Maillard, 1217 Meyrin Geneva, Switzerland b Department of orthopedic surgery and traumatology, Ghent university hospital, De Pintelaan 185, 9000 Gent, Belgium c CIM SA, centre d’imagerie médicale, 40a, route de Malagnou, 1208 Geneva, Switzerland Received 17 March 2016; received in revised form 13 June 2016; accepted 1st August 2016 Available online 15 September 2016
Abstract The diagnosis of nerve tumor(s) must be suspected in all cases of tumefaction or pain on the path of a nerve exacerbated by percussion. Solitary nerve tumors are primarily schwannomas, but other rare tumors may be present such as intraneural ganglion cysts of controversial origin. Preservation of nerve continuity is the underlying goal for any surgical procedure, irrespective of the type of tumor. Therapeutic outcomes are closely linked to tumor resectability; in most patients, the resectability of the tumor, its type and benignity can be predicted based on medical imaging. Comparison with the clinical examination and case-based reasoning is crucial. Consequently, the aim of this review was to examine the role of imaging in isolated benign peripheral nerve tumors, and provide the surgeon with a practical guide for its application in predicting the nature and resectability of nerve tumors. # 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved. Keywords: Peripheral nerve tumors; Neurofibroma; Schwannoma; Intraneural mucoid pseudocyst; MR nerve imaging; Ultrasound
Résumé Le diagnostic de tumeur nerveuse doit être évoqué en cas de tuméfaction ou de douleur sur le trajet d’un nerf que la percussion réveille. Les tumeurs nerveuses isolées sont en majorité des schwannomes ; les autres tumeurs sont beaucoup plus rares et d’une grande diversité histologique, comprenant les pseudo-kystes mucoïdes des nerfs dont l’origine est controversée. Quel que soit le type de tumeur, le traitement chirurgical vise à respecter la continuité nerveuse. Le pronostic est étroitement lié au caractère extirpable de la lésion. L’analyse radiologique permet, chez la plupart des patients, de prévoir l’extirpabilité, la nature et la bénignité des tumeurs. La confrontation avec l’examen clinique et la casuistique est essentielle. Le but de cette revue était d’analyser le rôle de l’imagerie en cas de tumeur nerveuse périphérique isolée et de faire une synthèse des critères cliniques et paracliniques qui permettront au chirurgien de prévoir au mieux le caractère extirpable et la nature des lésions. # 2016 SFCM. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Tumeurs des nerfs périphériques ; Neurofibrome ; Schwannome ; Pseudokyste mucoïde des nerfs ; IRM ; Échographie
1. Introduction * Corresponding author. E-mail addresses: [email protected] (G. Chick), [email protected] (N. Hollevoet), [email protected] (J. Victor), [email protected] (S. Bianchi).
Benign tumors of the peripheral nerves (BTPN) are rare tumors that can occur either as isolated lesions [1] or in multiple forms [2], as in neurofibromatoses (not included in this review).
http://dx.doi.org/10.1016/j.hansur.2016.08.001 2468-1229/# 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved.
G. Chick et al. / Hand Surgery and Rehabilitation 35 (2016) 320–329
Surgical treatment and prognosis vary greatly depending on whether the tumor is resectable, with the ultimate goal of the surgical procedure being the preservation of nerve continuity. Consequently, the aim of this review was to examine the role of imaging in isolated benign peripheral nerve tumors, and to provide the surgeon with a practical guide for its application in predicting the nature and resectability of nerve tumors. The general characteristics of benign nerve tumors (including patient presentation and radiological aspect) and specific features of the various tumor types are successively reviewed. 2. General characteristics of benign tumors of peripheral nerves
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discovery is made during surgery or imaging for nerve entrapment syndrome in young adults. More rarely, the diagnosis is made secondary to nerve resection performed erroneously for a diagnosis of lymphadenopathy (especially in the supraclavicular fossa), synovial cyst or resectable tumor [7]. 4. Radiological characteristics of BTPN Ultrasound (US) and magnetic resonance imaging (MRI) [8,9] are the reference imaging modalities for the diagnosis of BTPN. Computed tomography (CT) is rarely performed because of its low resolution for soft tissues. 4.1. US vs. MRI
BTPN represent approximately 1% of all soft tissue tumors [1]. While more frequent in the upper limb and mostly affecting large nerve trunks [3], ultimately any nerve can be affected. Eighty percent of BTPN are schwannomas [1,4]. BTPNs are rooted in either the nerve tissue or the non-neural elements of the nerve. From a practical and prognostic perspective, resectable tumors should be distinguished from non-resectable ones (Table 1). Essentially, resectable tumors grow eccentrically from the nerve, pushing back the fascicle groups without penetrating the perineurium and can be enucleated without disrupting nerve continuity. On the other hand, nonresectable tumors infiltrate all constituent elements of the nerve, with nerve fiber damage always occurring upon complete removal. Consequently, an epineurotomy for decompression is recommended in case of nerve compression symptoms [1,5]. 3. Patient presentation Most patients present with swelling over the course of a superficial nerve or, more rarely, localized pain and/or paresthesia revealed by percussion if a deeper nerve is involved [5,6]. BTPNs are solely responsible for neurological deficits by compressive intraneural damage (non-resectable tumors), development in a narrow anatomical groove or development spanning many years (resectable tumors). In some cases, its
As a general rule, peripheral nerves are more visible when surrounded by tissues of a different echostructure. Peripheral nerves appear as tubular structures made of hypo-echoic nerve fascicles embedded in a hyperechoic connective tissue corresponding to the epineurium. Longitudinally, US images present a fascicular pattern, and transversely, fascicles appear rounded or oval in shape, giving the nerve the typical honeycomb appearance [10,11]. US diagnosis of a nerve tumor is based on the existence of a mass in continuity with the nerve at its proximal and distal poles [12]. While US eliminates the vast majority of false tumor lesions and allows for differentiation between lymphadenopathy, neuroma or liquid tumor (hematoma, abscess or thrombosed aneurysm), it is more operator-dependent than MRI with nerve lesions rarely being specific. Color Doppler ultrasound allows an accurate assessment of the presence of intralesional flow and helps in differentiating solid and cystic lesions [12]. Its dynamic method of study enables the physician to analyze the entire nerve course and look for other remote tumor [10]. USguided pressure through the transducer on the mass can reproduce local pain and peripheral paresthesia (the so-called ‘‘ultrasonographic Tinel sign’’). This can be very helpful when assessing small peripheral lesions. But ultimately, US cannot replace MRI for determining the topography, the exact extent of tumor formation or the presence of invasion [13]. The boundary between the tumor and the nerve is sometimes difficult to
Table 1 Classification and origin of main single benign peripheral nerve tumors. Benign peripheral neural sheath tumors (PNSTs)
Peripheral non-neural sheath tumors
Schwannomaa
Intraneural hemangioma
b
Neurinoma Neurilemmomab
Neurofibroma
b
Perineural hemangioma Schwann sheath hemangiomab Intrinsic hemangioma of the peripheral nerveb (Extrafascicular intraneural hemangioma)a
Fibrolipomatous hamartoma b
Fatty infiltration Lipofibromab Intraneural lipofibromab
Intraneural lipomaa
Intraneural ganglion cyst Intraneural mucoid pseudocystb Nerve sheath ganglionb Intraneural synovial cystb
Neuro-fibrolipomab Fibro-fatty proliferationb
Traumatic neuromas and pseudoneuromas (following nerve injury) are excluded. Desmoid tumors and neuromuscular choristoma (benign triton tumor) of controversial origin are excluded. a Resectable tumors. b Equivalent nerve tumor terms.
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Table 2 Similarities and differences between isolated benign peripheral sheath tumors (general and MRI features).
Predominant age (years) Sex ratio (male/female) Location (most common) Macroscopic appearance
Condition of parent nerve T1-weighted signal T2-weighted signal
Enhancement intensity
Particularities Cystic and solid changes Target sign Fascicular sign Split fat sign
Schwannoma
Solitary neurofibroma
20–50 1 Supraclavicular brachial plexus Encapsulated, globular, pale yellow Eccentric ++
20–30 8.7 Supraclavicular brachial plexus Non-encapsulated, fusiform
Hypo- or iso-intense/muscle Hyperintense/fat
Diffuse ++ Predominantly peripheral ++ + ++ ++
Nerve cylindrical expansion Iso-intense/muscle Peripheral hyperintensity (target sign +++) Variable, moderate Central ++
+++ +? +
determine because the nerve may be distended and stretched over the mass. The neural origin of a mass from a small nerve (single hypo-echoic fascicle) is also very difficult to determine, particularly in superficial lesions [12]. Nevertheless, the use of high-frequency transducers has led to better detection of smaller nerves. MRI evaluation consists of different sequences (e.g., T1, T2, FAT SAT, IV Gadolinium), with images in the same plane (usually axial) supplemented by at least one other sequence in an orthogonal (sagittal, coronal) plane. The use of coils dedicated to the anatomic region of interest improves the homogeneity of the signal and spatial resolution. Positioning the patient and area for exploration at the magnet center is essential for ensuring high quality images. These can be further improved by contrast enhancement, 3D or 4D images, tractography or by magnetic resonance angiography (MRA), depending on the type of lesion. Gadolinium-enhanced images
must always be obtained to provide conclusive differentiation between a cystic and a solid lesion. A normal nerve has intermediate signal intensity, identical to muscle on T1 and T2 sequences. It is best viewed on T1 sequences in fatty layers or on T2-weighted fast SE and T2 fatsuppressed sequences, where it appears hyperintense compared to muscle [14]. There is no nerve enhancement after contrast injection. When dealing with a mass located in the region of a nerve, MRI allows a diagnosis in 75% of cases. Coronal and sagittal images provide individualization of the nerve’s entry and exit of the tumor [15]. Some signs (target sign, fascicle appearance, split fat sign) are especially suggestive of the benign nature of the lesion [12,13,16] and the combination of sequences and images after enhancement by contrast medium may reveal the nature of the tumor (Tables 2 and 3) [8,17]. Bone overlays do not interfere with scanning, unlike in US. In patients with signs of neurological deficits, it helps to assess the state of the nerve and the impact of denervation on the affected muscles [17,18]. MRI makes it possible to differentiate between a soft tissue tumor compressing the nerve, lymphadenopathy, thrombosed hemangioma, saccular aneurysm or neuroma. However, small movements can lead to artifacts and hinder interpretation of the images (need for complete immobilization during image acquisition). Furthermore, in contrast to US, MRI does not allow dynamic examination, allowing only a focused examination without the possibility of a panoramic study. 4.2. Computed tomography Computed tomography (CT) only shows the nerve as a nonspecific structure of intermediate density; it is a complementary diagnostic tool, except in very specific regions of the brachial plexus. Like standard radiographs, it may be helpful in visualizing an underlying bone abnormality. 5. Radiological characteristics by tumor type 5.1. Schwannomas 5.1.1. General considerations Schwannomas are observed at all ages, but most often between 20 and 50 years without a sex predominance [5,6,19].
Table 3 Similarities and differences between various types of isolated benign peripheral non-neural sheath tumors (general and MRI features). Intraneural lipoma
Fibrolipomatous hamartoma
Intraneural hemangioma
Intraneural ganglion cyst
Predominant age (years) Sex ratio (male/female) Location (most common) Macroscopic appearance Condition of parent nerve T1-weighted signal
40–60 Female > Male Median n Encapsulated, oval, yellow
10–20 Female +++ Median n Non-encapsulated locular
40 Male ++ Common peroneal n Translucent mass encapsulated
Heterogeneous signal
Iso- or hypo-intense/muscle
T2-weighted signal
High (similar to fat)
< 30 1 Median n (exclusive) Fusiform Nerve enlargement Coaxial cable-like (coronal) Spaghetti-like (sagittal) Coaxial cable-like (coronal) Spaghetti-like (sagittal)
Hyperintense
Hyperintense Muscle denervation
Enhancement intensity Particularities
No enhancement Low signal (STIR)
n: nerve.
High (similar to fat)
Slowly hyperintense enhancement
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Fig. 1. Isolated benign peripheral sheath tumors (ulnar nerve at the wrist): schwannoma: macroscopic appearance (A). Ultrasound: isolated globoid mass located along the nerve and eccentric to the nerve axis with homogeneously hypo-echoic structure with posterior acoustic enhancement (B). MRI: coronal FS T1-weighted following IV contrast: round mass with central enhancement, in direct continuity with nerve at its proximal and distal poles (C). S: schwannoma. White arrowheads: ulnar nerve. FS: fat suppression. Solitary neurofibroma: intraoperative view (D). Sagittal US imaging shows a fusiform iso-echogenic lesion (NF) with the nerve (white arrowheads) centrally entering and exiting the mass. Note again the centrally located nerve entrance and exit (E). MRI: sagittal proton density with fatsuppressed weighted image (F). NF: neurofibroma.
They are most common in the upper limbs (70%) [5,15,20], and are mainly located proximally to the brachial plexus (44%) and on peripheral nerve trunks (26%) [5,20]. In the lower limbs, the trunk of the sciatic nerve or the common peroneal nerve are most frequently affected [5]. Their macroscopic appearance is quite discernible, with an encapsulated, generally rounded, pale yellow tumor, located off-center in continuity with the nerve (Fig. 1A). Size varies depending on location, although most schwannomas are less than 2.5 cm in diameter [3]. 5.1.2. Radiological investigations No image is specific of schwannoma [15,18,21–23]; the noncentered nature of the tumor relative to the nerve, which is usually assessed on axial images, appears to be the most defining feature of a schwannomatous nerve tumor [24] (Table 2). 5.1.3. US Most schwannomas have the shape of a globoid mass with clearly defined margins, off-centered along the nerve [10], with a homogeneous or a more or less heterogeneous hypo-echoic
structure, with or without posterior contrast enhancement, depending on their cystic or solid internal appearance [12,18] (Fig. 1B). Schwannomas are most often hypervascular on color Doppler, followed by neurofibromas [13]. Although internal flow signals in a BTPN suggest a schwannoma, US does not allow definitive differentiation from a neurofibroma [13]. 5.1.4. MRI A schwannoma appears as an eccentric globular mass located on a neurovascular bundle when a large-caliber nerve is affected. The signal of the mass is hypo-intense or iso-intense on T1-weighted images and hyperintense, heterogeneous or not, on T2-weighted images, depending on intrinsic changes in the tumor (Fig. 1C). Sometimes a hypo-intense pseudocapsule corresponding to the epineurium is visible. It appears well defined, readily surrounded by a halo of fat (split fat sign) [19]. In some cases, the appearance of a target corresponds to a central hypo-intensity (fibrous tissue region) on T2-weighted images surrounded by a peripheral hyperintensity (myxoid region) [17,25]. In this case, gadolinium injection enhances the signal [22]. The fascicular sign corresponds to multiple small
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ring-like structures (with peripheral higher signal intensity) on either T2- or proton density-weighted MR imaging [16,17,22,26]. Schwannomas are more commonly associated with a fascicular [22] and split fat sign [18] than neurofibromas; a target sign is more common in neurofibroma (Table 2). 5.1.5. CT Most schwannomas appear as a round or oval mass that is off-center relative to the nerve, hypodense (or more rarely isodense) compared to the muscle, and homogeneously or heterogeneously enhanced after injection of contrast medium, depending on the predominant cellular components and the cystic and/or hemorrhagic changes [25], giving it the target sign [17].
or oval (spindle neuroma) in the axis of a severed or damaged nerve [16,19] and is dissociated from the nerve fascicles. The echostructure is sometimes mixed, with characteristic sensitivity to probe passage. On MRI, the neuroma has the same hypo-intense signal intensity as the muscle on T1-weighted images, but is hyperintense compared to the muscle on T2weighted images; enhanced again after contrast [16]. Plexiform neurofibroma is seen exclusively in Von Recklinghausen neurofibromatosis. MRI shows a convoluted mass composed of countless neurofibromas developed from the nerve fascicles in the affected nerve trunk, typically on a long portion with side branches [29], creating the appearance of a ‘‘bag of worms’’ [26]. 5.3. Intraneural lipoma
5.2. Solitary neurofibroma 5.2.1. General considerations Solitary neurofibromas represent 10% of isolated nerve tumors, usually affecting young adults [6] between 20 and 30 years old, with a male/female ratio of 8.7 [5]. They are often located proximally (supraclavicular plexus 55%, major nerve trunks 45%) in the upper limbs [5,27], while in the lower limbs, pelvic plexus and sciatic nerve involvement is common [5]. It is a non-encapsulated tumor (always demarcated) growing inside the nerve that encases each fascicle and stretches it, leading to the appearance of an irregular cylindrical expansion of the nerve (Fig. 1D). 5.2.2. US Neurofibromas, which are intimately mingled with the nerve tissue, are characterized by a fusiform swelling (not globoid), with nerve fibers entering and exiting the ends of the swollen area (Fig. 1E). They are well-defined masses with sharp borders that usually have a hyp-oechoic appearance. Contrary to schwannomas, they do not contain anechoic areas. Internal calcifications are rare. Unlike schwannomas, ultrasound imaging in the axial plane does not result in visible nerve fascicles. Neurofibromas are less hypervascularized on color Doppler than schwannomas [12,26]. 5.2.3. MRI Neurofibromas appear elongated and usually have signal intensity identical to that of muscle on T1 sequences. Enhancement is usually moderate and variable after contrast medium injection [28] (Fig. 1F), while the target sign in T2 (initially described as pathognomonic) is often non-specific [17,26,28] (Table 2). 5.2.4. CT The neurofibroma is hypodense. Sometimes a target is present (central hyperdensity, peripheral hypodensity). 5.2.5. Differential diagnosis The differential diagnosis of solitary neurofibroma includes schwannoma, neuroma and plexiform neurofibroma. The neuroma appears hypo-echoic, rounded (terminal neuroma)
5.3.1. General considerations Intraneural lipomas are extremely rare with just 15 cases reported in the literature [1,5,30,31]. Prior to histological identification, these lipomas were often mistaken for fibrolipomatous hamartoma [31]. Intraneural lipomas develop predominantly in female patients between the ages of 40 and 60 years. Their slow growth explains the high tolerance rate. Lesions are typically located on the median nerve (causing clinical signs of carpal tunnel) but have been reported on other nerves as well [1,5,7,31]. Intraneural lipomas appear as an encapsulated tumor [1,31,32], usually > 5 cm in diameter with nerve fibers running along its surface (Fig. 2A). Thus, complete excision without nerve damage is possible [32]. Some intraneural lipomas seem to originate in individual nerve fascicles and can cause a mass effect on the affected nerve. Histological examination reveals that these tumors consist exclusively of adipose tissue without neural elements [31,32]. 5.3.2. US Intraneural lipomas appear as hyperechoic oval masses with well-defined borders. Color Doppler typically shows no blood flow signals inside the mass. 5.3.3. MRI The MRI appearance is similar to that of other locations with a soft tissue tumor that is clearly defined, having the same signal characteristics as subcutaneous fat in all sequences. On T1 and T2 sequences, the signal intensity is notably high, while on T2-weighted sequences obtained with fat saturation, the signal intensity is low with the nerve fascicles around the viewable mass (Fig. 2B) [32]. No enhancement is observed after contrast injection (Table 3) [7,32]. 5.3.4. Differential diagnosis The differential diagnosis for intraneural lipoma includes extrinsic lipoma compressing a nerve, fibrolipomatous hamartoma or a well-differentiated liposarcoma. In case of liposarcoma, some suspicious signs are heterogeneous appearance (nodules or non-fatty areas), poorly defined margins, size larger than 5 cm or atypia (calcifications, septa thickening by more than 2 mm and bleeding). Importantly, MRI with
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Fig. 2. Isolated benign peripheral non-neural sheath tumors. Intraneural lipoma: macroscopic aspect: well-encapsulated intraneural lipoma that spread the nerve fibers (digital nerve) (A). MRI: sagittal SE T1-weighted image (left) of the wrist showing a mass that has the same signal intensity as subcutaneous fat within the median nerve. Sagittal SE T2-weighted image (right) with fat suppression at the same level shows complete saturation of signal within the mass, confirming that it is fat (B). Note the fascicles of the median nerve draped around the superior aspect of the mass (Reproduced by kind permission of Elsevier from Amrami et al. [18], L: intraneural lipoma). Intraneural extrafascicular hemangioma of the median nerve (CDE): macroscopic appearance (C) and after removal (D). H: hemangioma; blue arrowhead: flexor carpi radialis tendon; white arrowhead: median nerve. MRI: axial SE T1-weighted image IV: high signal intensity with moderate enhancement after intravenous contrast administration as well as tubular structures suggesting feeding or draining vessels (blue arrowhead: median nerve) (E).
gadolinium injection is necessary to search for a fibrous component (fibrolipoma) or sarcomatous transformation [33]. 5.4. Intraneural hemangioma 5.4.1. General considerations Unlike vascular malformations, which are the result of abnormal vasculogenesis with normal endothelial renewal, hemangiomas are tumors involving cell proliferation [34]. Intraneural hemangioma are extremely rare, almost exclusively observed in females often during the first decade of life [1,35– 37], with median nerve most commonly affected [35–37]. An intraneural hemangioma has the same characteristics as the conventional hemangioma, from which it is distinguished only by its location. The intraneural hemangioma can have an extrafascicular (Fig. 2C and D), intrafascicular or mixed development [36]. Depending on the degree of intrafascicular invasion, excision is not possible without sacrificing the nerve [35,36]. Extrafascicular forms are resectable tumors (Table 1). 5.4.2. US Hemangiomas can always be characterized by US, especially if phleboliths (which appear as hyperechoic small structures with posterior shadowing) are present on standard radiographs. A hemangioma appears as a tissue mass with mixed echogenicity with poorly defined borders. The mass may show an arterial (fast flow) or a weak venous Doppler signal (slow flow). 5.4.3. MRI MRI (Fig. 2E) shows an infiltrating, poorly defined mass with heterogeneous signal intensity, and dilated and serpiginous vascular structures that may contain phleboliths, enhancing
very slowly after contrast medium injection. Fatty spots are scattered throughout the tumor in T1; this can sometimes determine whether the lesion is intra- or extraneural. T2weighted images have the characteristic appearance of hyperintense clusters [38] (Table 3). 5.4.4. Magnetic resonance angiography (MRA) MRA is a non-invasive 3D imaging technique that allows vascular structures to be delineated [39]. MRA can objectify the afferent and efferent vessels of the hemangioma [40]. Complementarily to MRI and color Doppler ultrasound, MRA is useful in assessing the extension of the tumor process [39,41]. The evolution of 4D-MRA and ‘‘time-resolved’’ (TRMRA/dynamic MRA) should be considered as a valuable alternative to conventional MRA in the imaging of vascular pathologies [42]. 5.4.5. Differential diagnosis The differential diagnosis includes extraneural hemangioma, thrombosed aneurysm, hypervascularized soft tissue tumor or arteriovenous malformation. In a thrombosed aneurysm, there is a heterogeneous hyperechoic area around the aneurysm (thrombus) with a pulsatile back-and-forth flow revealed by a color Doppler. In an arteriovenous malformation, there is no tissue component and presence of an early venous return. 5.5. Fibrolipomatous hamartoma 5.5.1. General considerations Fibrolipomatous hamartoma of the nerve has been described using equivalent terms such as fatty infiltration, lipofibroma, fibro-fatty proliferation, and intraneural lipofibroma. The
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fibrolipomatous hamartoma is a rare tumor, probably of congenital origin [43]. Approximately 100 cases have been reported in the literature [44,45], mostly involving young adults under the age of 30, with no gender imbalance [44,46]. The preferred sites are the median nerve and its side branches. It presents as soft swelling of the distal forearm [46], wrist or palm existing since childhood, often asymptomatic, sometimes bilobated on either side of the carpal tunnel, and associated with macrodactyly in 30% of cases [44,46]. The mass grows slowly, causing median nerve compression signs. The affected nerve appears enlarged due to fibro-fatty endoneural, perineural and epineural infiltration [32], which can cause the nerve to reach up to three times its normal size (Fig. 3A and B). 5.5.2. Standard X-rays X-rays show edema of the soft tissues in the affected area with or without macrodactyly. There may be bone hypertrophy with signs of osteoarthritis [46]. 5.5.3. US US reveals a fusiform mass with longitudinally distributed nerve fascicles marked by hyper- and hypo-echoic bands [26,46]. As described by Toms et al. [47], these tumors appear as ‘‘characteristic hypo-echoic coaxial cabling encased by an echogenic substratum’’ (Fig. 3C). 5.5.4. MRI The MRI appearance is pathognomonic [18,46,48,49], with hypertrophy of the median nerve (up to 1.6 cm2 in caliber), with round, oval or multilocular shape, which has a hyperintense signal similar to fat, with individuation of hypo-intense longitudinal bands along the axis of the nerve corresponding to the fascicles. In T1 and T2 sections, this contrast gives a coaxial ‘‘cable-like’’ appearance on axial images and
‘‘spaghetti-like’’ appearance on coronal and sagittal images (Fig. 3D and E) [26,32,46,48]. Fine hypo-intense septa inside the fat tissue separate the nerve fascicles (Lotus sign): these correspond to the typical feature of perineurium thickening (Table 3). 5.5.5. CT The CT scan shows a mass inside the carpal tunnel causing the flexor retinaculum and tendons to shift over. The dense part of the mass has fibroblastic elements [46]. 5.6. Intraneural ganglion cyst 5.6.1. General considerations Intraneural ganglion cysts are characterized by infiltration of the nerve by a mucoid substance, thereby forming an intraneural tumor. The hypothesis of a joint origin from a joint nerve branch is the most commonly accepted one [50–52]. The tumor is usually revealed by a sharp pain or symptoms of nerve compression, followed by neurological deficit in the corresponding nerve segment, as the pain fades. The time between the first symptoms and diagnosis is relatively short (3 to 7.4 months) [53]. This is explained by the rapid growth of the pseudocyst and the presence of a neurological deficit that often alarms the patient. While a short series has been published, most cases are isolated, affecting men in their 40s [50,51,53,54]. The lesions affect mostly mixed nerves. The preferential site is the common peroneal nerve in the fibular neck [53]. Other sites have the particular characteristic of being near a joint or a narrow anatomical groove. The ulnar nerve in the elbow is the most common site in the upper limb [53]. Intraneural ganglion cysts appear as a single or multiple translucent mass encapsulated in the nerve trunk. The nerve fascicles on the outer surface are often dilacerated and integrated into the wall (Fig. 4A).
Fig. 3. Fibrolipomatous hamartoma of the median nerve at the wrist: macroscopic appearance (A) and after epineurotomy (B). Ultrasound appearance with color Doppler (C): hypo-echoic thickened axonal bundles interspersed in echogenic fatty tissue with no intralesional blood flow. The median nerve is outlined in this axial view, which demonstrates the coaxial ‘‘cable-like’’ appearance. MRI axial T1-weighted image of wrist shows thickened hypodense nerve fascicles surrounded by hyperintense fibro-adipose tissue giving it a coaxial ‘‘cable-like’’ appearance (white arrowhead) (D). MRI Sagittal T1 fat saturation IV weighted image shows ‘‘spaghetti-like’’ appearance of the lesion (white arrowhead) (E).
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Fig. 4. Intraneural mucoid pseudocyst (common peroneal nerve): Intraoperative view (A): intraneural mucoid cyst of the common peroneal nerve (green arrowhead) with peroneal intraneural ganglion arising from the superior tibiofibular joint and extending along the articular branch (blue arrowhead) to the common peroneal nerve. MRI (B): sagittal T2-weighted image shows cyst arising from the superior tibiofibular joint and extending to the common peroneal nerve and its branches (black arrowheads). Delayed CT arthrography (C): curved multiplanar reformatted CT image shows a long, thin pedicle between the cysts at the anterior aspect of the tibiofibular joint and the intraneural cyst (white arrow) (courtesy of J. Malghem, MD).
5.6.2. Electromyography (EMG) EMG simply confirms potential nerve damage and specifies the compression site. 5.6.3. US US can locate the delimited lesion and its fluid nature (anechoic or quasi-anechoic mass, sometimes multilocular with posterior enhancement of the signal). However, the resolution is often insufficient to clarify the relationship between the cyst and neighboring joint; in general, US cannot distinguish the communicating pedicle of the cyst, which is long and thin [54]. 5.6.4. MRI MRI confirmed the tumor’s fluid nature, its location and extension. The signal is iso-intense or hypo-intense relative to the muscle on T1-weighted images. On T2-weighted images, the signal is intense, with well-defined and sometimes multilocular rims. Only the signal of thin walls is enhanced rapidly upon injection of intravenous contrast agent. The nerve fascicles shift to the margins of the intravenous cyst in a crescentic intraneural fashion, giving a ‘‘signet ring’’ appearance. The nerve itself may show a moderate enhancement and hyperintensity in T2 images related to the mass effect. The sagittal images indicate the state of the nerve, which is laminated and thinned. The appearance of the pedicle may vary, depending on its liquid contents: it is only visible in one in four cases, when it may be identified on the joint CT scan [54]. The use of 3D reconstructed images (Fig. 4B) can facilitate its detection [51,52]. In the event of motor or previous damage, the MRI can reveal signal abnormalities in the affected muscles, which may have visible signs of denervation such as muscle edema, adipose involution and muscle atrophy. MRI can confirm recurrence, and may be useful for long term monitoring (Table 3). 5.6.5. CT CT objectifies the content of the cyst, with a density slightly lower than that of the muscles, and a well-defined, sometimes multilobular appearance. The wall of the cyst can be viewed using intravenous iodinated contrast medium.
5.6.6. CT arthrography CT arthrography is not the method of choice for diagnosing mucoid cysts. However, it is an efficient method for proving the existence of a pedicle communicating with the joint, which is of surgical interest [50,54]. CT arthrography images must be obtained several hours after the intra-articular injection of the contrast medium (Fig. 4C), due to slow diffusion of the contrast in the cystic gelatinous material [52,54,55]. 5.6.7. Differential diagnosis The differential diagnosis for intraneural ganglion cyst includes other peripheral nerve tumors (cystic schwannomas), malignant tumor with myxoid contents, juxta-articular synovial cyst compressing the nerve, hematoma, aneurysm of the popliteal artery, intramuscular or juxta-articular myxoma or entrapment syndrome. 6. Future directions Imaging sensitivity and specificity have increased greatly with the help of metabolic positron emission tomography (PET), and will continue to increase in the future with functional magnetic resonance spectroscopy and diffusion tensor imaging. The information provided by contrast image diffusion (tractography imaging) will be crucial for obtaining data on the integrity of the nerves in both benign and malignant lesions of the peripheral nerves. Tractography is a new MRI technique that allows assessment of the internal microarchitecture of peripheral nerves. BTPN and entrapment neuropathies have been evaluated using tractography; however, this technique is no longer used during routine evaluation of peripheral tumors because of a lack of harmonization of the protocols and data post-processing methods [56]. Diagnostic methods are moving towards a combination of metabolic, functional and anatomical images, to assist in the differentiation of diverse clinical entities [21]. 7. Conclusion Both US and MRI of large-caliber nerves can confirm the neural nature of a tumor. While US is the primary imaging modality, due to its ease of use, low price and accessibility, MRI
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remains the gold standard as it is able – in the vast majority of cases – to identify the type of tumor and importantly, determine its resectability. While imaging is crucial in the diagnostic work up of patients suspected of or presenting with benign tumors of peripheral nerves, it is essential that clinicians understand that imaging is just one tool in their arsenal. A robust clinical examination is indispensable, with close cooperation between the surgeon, radiologist and histologist being essential. But even after a robust clinical examination combined with extensive secondary imaging, the tumor’s resectability is sometimes only known following an epineurotomy. Disclosure of interest The authors declare that they have no competing interest. Acknowledgements We are grateful to Mathew Wilson, PhD, for reviewing the English version of this manuscript. References [1] Chick G, Alnot JY, Silbermann-Hoffman O. Benign solitary tumors of the peripheral nerves. Rev Chir Orthop Reparatrice Appar Mot 2000;86: 825–34. [2] Chick G, Alnot JY, Silbermann-Hoffman O. Multiple peripheral nerve tumors: update and review of the literature. Chir Main 2003;22:131–7. [3] Forthman CL, Blazar PE. Nerve tumors of the hand and upper extremity. Hand Clin 2004;20:233–42. [4] Sandberg K, Nilsson J, Søe Nielsen N, Dahlin LB. Tumours of peripheral nerves in the upper extremity: a 22-year epidemiological study. Scand J Plast Reconstr Surg Hand Surg 2009;43:43–9. [5] Kim DH, Murovic JA, Tiel RL, Kline DG. Operative outcomes of 546 Louisiana State University Health Sciences Center peripheral nerve tumors. Neurosurg Clin N Am 2004;15:177–92. [6] Kehoe NJ, Reid RP, Semple JC. Solitary benign peripheral-nerve tumours. Review of 32 years’ experience. J Bone Joint Surg Br 1995;77:497–500. [7] Matsuo T, Sugita T, Shimose S, Kubo T, Yasunaga Y, Ochi M. Intraneural lipoma of the posterior interosseous nerve. J Hand Surg [Am] 2007;32:1530–2. [8] Dorsi MJ, Belzberg AJ. Peripheral nerve tumors of the extremities. In: Schmidek HH, Roberts DW, editors. Schmidek and Sweet’s operative in neurosurgical techniques. 6th ed., Philadelphia: Elsevier; 2012. p. 2319–27. [9] Hems TE, Burge PD, Wilson DJ. The role of magnetic resonance imaging in the management of peripheral nerve tumours. J Hand Surg [Br] 1997;22:57–60. [10] Bianchi S. Ultrasound of the peripheral nerves. Joint Bone Spine 2008;75:643–9. [11] Martinoli C, Bianchi S, Cohen M, Graif M. Ultrasound of peripheral nerves. J Radiol 2005;86:1869–78. [12] Valle M, Zamorani MP. Nerve and blood vessels. In: Bianchi S, Martinelli C, editors. Ultrasound of the musculoskeletal system. Berlin: SpringerVerlag; 2007. p. 97–134. [13] Garcia J, Bianchi S. Diagnostic imaging of tumors of the hand and wrist. Eur Radiol 2001;11:1470–82. [14] Grant GA, Britz GW, Goodkin R, Jarvik JG, Maravilla K, Kliot M. The utility of magnetic resonance imaging in evaluating peripheral nerve disorders. Muscle Nerve 2002;25:314–31. [15] Nilsson J, Sandberg K, Søe Nielsen N, Dahlin LB. Magnetic resonance imaging of peripheral nerve tumours in the upper extremity. Scand J Plast Reconstr Surg Hand Surg 2009;43:153–9. [16] Abreu E, Aubert S, Wavreille G, Gheno R, Canella C, Cotten A. Peripheral tumor and tumor-like neurogenic lesions. Eur J Radiol 2013;82:38–50.
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