How Big Is Morton’s Neuroma?

Morton’s neuroma, also known as intermetatarsal neuroma, plantar neuroma or interdigital neuroma is the entrapment of the regional nerve, the common plantar digital nerve, supplying the toes and phalanges. The most common theory regarding the development of the condition is that common plantar digital nerve is compressed by the transverse intermetatarsal ligament. The chronic pressure and compression leads to irritation of the nerve, which results in nerve fibrosis and nerve inflammation leading to the ensuing symptoms of pain and paresthesias.

In actual, the name Morton’s neuroma is a misnomer as the condition does not usually depict an actual tumor or growth, but fibrosis or scarring of the nerve tissue due to repeated stress. The pressure can be caused due to high heels or narrow toe box footwear, therefore, seen more commonly in females than in males. However, males with injury to the forefoot region, high arch or flat foot may be affected by the condition. The condition is also related to certain high impact occupation in which a lot of walking or exercise is involved and a lot of stress is placed on the forefoot.

The most commonly affected area is the third and fourth toes, rarely the second and the third toes, with the involvement of only one foot. The symptoms involve excruciating pain that is sharp, electric, burning pain that radiates from the point of origin, which is the third and second metatarsal space in most cases. The pain is accompanied by numbness and tingling in the toes. The symptoms may be intermittent with infrequent flare ups, which become frequent with passing time and unattended condition.

Although, the lump cannot be felt as the neuroma is deep seated and size of it difficult to depict as it is not visible to naked eyes. The size and location of the actual neuroma is only depicted by imaging studies. Both, ultrasound and magnetic resonance imaging of the foot have been sensitive in finding the location and the size of Morton’s neuroma. Imaging is mandatory for the definitive diagnosis for the location, size and number of lesions. There have been cases with multiple lesions and these cases can only be identified with imaging studies rather than clinical evaluation.

Imaging studies of Morton’s neuroma show that the most common location of the neuroma is between the third and fourth metatarsal head followed by the second and third intermetatarsal space. Usually, the size of Morton’s neuroma is very small and in most cases is around 6 mm and not less than 3 mm. Although, both ultrasound and MR imaging are equally sensitive in detection of Morton’s neuroma, the size of neuroma is comparatively larger in MR imaging. In addition, the size of Morton’s neuroma is comparative and changeable and highly dependent on pronation or supination position of the foot, the increased size of Morton’s neuroma is found when the foot is in prone position, such as in plantar flexion of ankle. Therefore, the size of the neuroma detected by imaging is affected by the position of the patient as well as the pressure on the neuroma.

Most of the studies show better clinical outcome in symptomatology with Morton’s neuroma excision when the neuroma is greater than 5 mm, and these institutions are of the opinion that symptoms worsen with increased size of the Morton’s neuroma. There also has been an institution of thought that believes that the manifestations of symptoms are not correlated to the size of Morton’s neuroma and the symptoms do not worsen with the increase in size of the intermetatarsal neuroma. Morton’s neuroma less than 3 mm are not appreciated in either the ultrasound of MR imaging, but the patients have still been symptomatic. Therefore, both the clinical manifestation and the imaging studies should be taken into equal consideration and analyzed as appropriately as possible. Whether the size of Morton’s neuroma affects symptomatology is still debatable, but the management should depend on the physician’s discretion aiming towards relief in symptoms.

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