You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Morton NeuromaArticle Last Updated: Apr 13, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Steven Needell, MD, Director of Musculoskeletal Imaging, Department of Radiology, Boca Raton Community Hospital Steven Needell is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, and Radiological Society of North America Coauthor(s): Jonathan Cutler, DPM, Consulting Staff, Western Communities Foot and Ankle Center Editors: Michael A Bruno, MD, Associate Professor, Departments of Radiology and Medicine, Pennsylvania State University College of Medicine; Director, Radiology Quality Management Services, Milton S Hershey Medical Center, Pennsylvania State University College of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; William R Reinus, MD, MBA, FACR, Professor of Radiology, Temple University; Chief of Musculoskeletal and Trauma Radiology, Vice Chair, Department of Radiology, Temple University Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related keywords: Morton's neuroma, interdigital neuroma, Morton neuralgia, interdigital nerve, intermetatarsal space, medial plantar nerve, medial and lateral plantar nerve INTRODUCTIONSection 2 of 11
  Morton neuroma, or interdigital neuroma, is a common condition that involves enlargement of the interdigital nerve of the foot. Morton neuroma most commonly affects the third intermetatarsal space, but it can also affect the second intermetatarsal space, although it does so less often. Lesions in the fourth and first interspaces are unusual. The etiology remains controversial, and treatment varies among practitioners. Diagnosing the condition involves clinical judgment, and in difficult cases, imaging may be useful in determining the precise diagnosis. ANATOMYSection 3 of 11
The medial and lateral plantar nerves, which are terminal branches of the tibial nerve, supply most of the innervation for the digits of the foot. The medial plantar nerve divides at the base of each metatarsal into 3 nerves that supply the branches to digits 1-3. The lateral plantar nerve divides into superficial and deep branches. The superficial branch supplies cutaneous innervation to toes 4 and 5 and also sends a communicating branch to the medial plantar nerve to innervate the third interspace. PATHOPHYSIOLOGYSection 4 of 11
The etiology of Morton neuroma is controversial. Histologic findings include neural degeneration, epineural and endovascular hyalinization, and perineural fibrosis.1 Morton neuroma represents perineural fibrosis along the plantar nerve. Morton neuroma is not a nerve tumor, and it does not contain inflammatory cells or cystic components. In 1876, Morton believed that the etiology was related to compression of the nerve.2 He found that the plantar nerve stretches under the pulley of the transverse metatarsal ligament as the toes dorsiflex and as the belly of the flexor digitorum brevis muscle contracts. Nissen3 believed that an ischemic component existed and that it arose from compression from the transverse metatarsal ligament. Bossley and Cairney4 believed the etiology was secondary to an intermetatarsal bursa distal to the transverse metatarsal ligament, undergoing inflammatory changes that caused fibrosis around the nerve. Mulder agreed with Bossley and Cairney and determined that this enlarged bursa causes a click when the metatarsals are squeezed. This finding is called the Mulder sign.2 DIAGNOSISSection 5 of 11
Patients may report numbing, burning, and shooting pain that courses between the metatarsals into the digits. The symptoms usually are relieved when the affected areas are massaged and appropriate shoes are worn. Such shoes are wide in the toe box and have adequate cushioning, with heels no higher than 0.5-1 in. Many asymptomatic patients have clinically silent neuromas; therefore, careful assessment of clinical findings is essential in evaluating the significance of a lesion that is evident on magnetic resonance imaging (MRI) scans. Objective findings include tenderness dorsal to the metatarsal heads that reproduces an underlying pain upon compression of the nerve. The Mulder click can be distinguished by squeezing the metatarsal heads together (1-5 in the transverse plane) and by massaging the interspace in the vertical plane. A click (representing an enlarged nerve or inflamed bursa) can be felt and heard. DIFFERENTIAL DIAGNOSISSection 6 of 11
The differential diagnosis of Morton neuroma includes a stress fracture, a tendon sheath ganglion, a foreign-body reaction, a nerve-sheath tumor, strain of the plantar capsule, and capsulitis or bursitis at the level of the plantar metatarsal-phalangeal joint (MPJ).1, 5 Occasionally, the diagnosis can be challenging because, in addition to inflammation of the capsule or bursa, inflammation of the adjacent nerve also may be present, causing the neuritic sensation of a Morton neuroma. Peripheral neuropathy also can cause symptoms such as a burning or neuritic sensation, but these tend to occur throughout the toes and on both feet. Additional differential diagnoses with similar symptoms involve neoplasms and fibromas. Imaging studies, particularly MRIs, are a valuable tool in differentiating these conditions. IMAGINGSection 7 of 11
Although a Morton neuroma can often be confidently diagnosed on the basis of the clinical findings alone, imaging is useful in the preoperative setting or in cases with atypical symptoms.1 Morton neuromas have been imaged successfully by using MRI, CT scanning, and ultrasonography.5, 6 MRI has been the preferred imaging modality for demonstrating Morton neuroma largely because of MRI's superior contrast resolution and reproducibility. Ultrasonography has the advantage of being less expensive and more portable than MRI, but because of its high learning curve and dependence on the operator's skill, whether ultrasonography will replace MRI as the preferred imaging modality for this condition remains to be seen. Relatively few radiologists and technologists in the United States are experienced in using ultrasonography to diagnose Morton neuroma. The employment of ultrasonography in this diagnosis, although described in the literature, most commonly occurs in subspecialty academic settings and outside the United States. Not uncommonly, Morton neuromas are incidental findings on MRIs; they are detected best on short-axis (transverse) T1-weighted MRIs through the metatarsal heads. Morton neuroma is typically seen as a bulbous mass arising between the metatarsal heads. Because neuromas have a highly cellular and/or fibrous nature, lesions demonstrate low signal intensity on both T1- and T2-weighted images (see Images 1-2). The lesions are highly vascular and are typically enhancing after the intravenous administration of a gadolinium-based contrast agent.7 Contrast enhancement is best visualized on T1-weighted fat-saturated images. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis or nephrogenic fibrosing dermopathy (NSF/NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography scans. As of late December 2006, the US Food and Drug Administration (FDA) had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots onthe whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Reliably differentiating Morton neuroma from a normal plantar nerve is difficult unless the lesion is 5 mm or larger.8 An intermetatarsal space lesion that is bright on T2-weighted images is unlikely to represent a Morton neuroma. Lesions with hyperintense signal on T2-weighted images are more likely to represent a true neuroma, a synovial or rheumatoid nodule (see Image 3), or bursal fluid. The administration of contrast material assists in differentiating these entities because true neuromas are intensely enhancing, and bursal fluid is not enhancing.7 MRI findings in a suggested Morton neuroma effectively influence therapy. In one study, imaging findings changed the treatment plan in 57% of patients, with the withdrawal of the diagnosis in 28% and with changes in the location or number of detected neuromas in more than 33% of the feet of the remaining patients.8 Interspace lesions with low intensity appear on imaging studies in asymptomatic patients.1 Therefore, careful correlation with the clinical findings is essential prior to initiating therapy. TREATMENTSection 8 of 11
Conservative treatment Conservative treatment consists of shoe modifications as well as the administration of various types of medication. First, the patient should be advised to wear appropriate shoes. These should be wide in the toe box, have adequate cushioning, and feature heels no higher than 0.5-1 in. A narrow toe box causes the metatarsals to impinge on the nerve, which causes a neuritic-type symptom. A neuroma pad can be placed just proximal to the affected metatarsal head (second and third metatarsal heads for a second interspace neuroma). When the patient steps down, the neuroma pad is designed to separate the metatarsal heads to prevent rubbing or irritating the affected neuroma. Neuroma pads are most successful when used with an appropriate shoe, as described. Nonsteroidal anti-inflammatory drugs play a role in the conservative treatment of the neuroma. An oral anti-inflammatory drug can reduce the inflammation around the nerve and alleviate some of the symptoms. Cortisone injections delivered into the interspace at the level of the neuroma also can help in decreasing the amount of inflammation around the nerve. The use of no more than 4 injections is advised because they can decrease the fat pad and symptoms such as metatarsalgia may develop. Shoe modifications, neuroma pads, and cortisone injections are typically used concurrently to eliminate pressure on the nerve and to reduce inflammation around the nerve. Surgical treatment Surgical excision of the neuroma is indicated when conservative care does not satisfactorily alleviate the patient's symptoms. Surgery is usually performed from a dorsal approach to prevent scar formation on the plantar aspect of the foot. An incision is made over the affected interspace by means of sharp and blunt dissection. Care is taken to avoid the neurovascular structures. The deep transverse metatarsal ligament is released. The neuroma is usually situated on the plantar aspect of the interspace and is resected as proximally as possible. Branches to the 2 affected digits are cut as distally as possible. The nerve is sent for pathologic analysis to confirm the diagnosis, and the area is closed with absorbable suture material in the deep structures and with nonabsorbable suture material in the skin. SUMMARYSection 9 of 11
Neuromas are a common ailment seen by foot and ankle specialists. The diagnosis is often straightforward because of the description of a sharp, shooting pain or numbness in the affected digits. However, because the patients' descriptions of the pain can vary or because the pain can be related to another ailment in the differential diagnosis, MRI has become a useful imaging tool in obtaining a precise diagnosis. Ultrasonography also is commonly used. It is more widely available and less costly than MRI. Despite these advantages, the operator-intensive aspects of sonography, as well as its steep learning curve, are limiting factors. Whether ultrasonography will eventually replace MRI as the primary imaging modality for this condition remains to be determined. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Article Last Updated: Apr 13, 2007 | ||||||||||||||||||||||||||
