William Wardell DO, Colt Crymes MD, Brett Auerbach DO, Dana LaVanture MD
Guthrie/Robert Packer Hospital Orthopaedic Surgery

Abstract  

Introduction
Carpal tunnel syndrome is an exceptionally common median nerve entrapment neuropathy. It is rarely caused by space occupying lesions, such as lipomas, and in such cases these lesions are usually located within the carpal tunnel. Lipomas are the most common soft tissue tumor encountered in the body, with less than 1% occurring in the hand.  

Case Report
Reported is a case of a 55-year-old female with symptoms of carpal tunnel syndrome secondary to an extra-carpal tunnel, thenar intramuscular, lipoma. Surgical excision of lipoma with concomitant carpal tunnel decompression resulted in full neurological recovery.

Discussion
Intramuscular lipomas, even when extra-carpal tunnel in location, can result in carpal tunnel syndrome, secondary to increased pressure in the palmar space resulting in increased pressure in the carpal tunnel.  Clinical history and a comprehensive physical examination are critical in the diagnosis of carpal tunnel syndrome.  Carpal tunnel decompression and lipoma excision on their own provide an excellent prognosis, when used in combination for treatment of a rare intramuscular lipoma of the thenar musculature, they provide excellent patient recovery and outcomes, as demonstrated by this interesting case.  

Keywords: Lipoma, Carpal Tunnel Syndrome, Compression Neuropathy, Intramuscular Lipoma

Introduction  
Carpal tunnel syndrome (CTS) is an exceptionally common compression neuropathy caused by compression of the median nerve in the carpal tunnel. Patient presentation is typically consistent with paresthesia in the median nerve sensory distribution of the hand including the thumb, index and middle fingers.  Additional symptoms include weakness in musculature innervated by the median nerve including abductor pollicis brevis and opponens pollicis resulting in decreased ability to abduct and oppose the thumb (1,2).  Lipomas are the most common soft tissue tumors in the body and are typically asymptomatic in presentation, but they are found in the hand in <1% of cases (3). Common causes of carpal tunnel syndrome include: tenosynovitis of flexor tendons, accessory muscles, hypothyroidism, rheumatoid arthritis, diabetes mellitus, pregnancy and, rarely, space occupying lesions within the carpal tunnel(4). Due to the rare occurrence of lipomas in the hand, there are few reports of secondary carpal tunnel syndrome (5-11).  This is a particularly rare occurrence, especially when the lipoma is located in an extra-carpal tunnel and intramuscular origin, arising in the thenar eminence. Described is a rare case of secondary carpal tunnel syndrome due to thenar intramuscular lipoma.  

Case Report  
A 55-year-old female presented to the office with a chief complaint of numbness in the thumb, index, middle and the radial aspect of the ring finger of the right hand. She had noted that this condition had been present for three months in duration.  Additionally, the patient complained of progressive right-hand weakness, pain, and increased swelling along the thenar eminence. She experienced significant pain and weakness when attempting to grip objects. On physical examination there was a soft non-tender mass palpable in the thenar eminence. Plain radiographs of the hand were performed and were non-conclusive. Magnetic resonance imaging (MRI) was performed which demonstrated a 0.7 x 1.9 x 0.7 cm well circumscribed ovoid lesion within the body of the adductor pollicis brevis (Figure 1). Imaging characteristics were consistent with an intramuscular lipoma. Surgical excision was recommended to the patient. Carpal tunnel decompression with lipoma excision was performed under general anesthesia with a tourniquet in place. The mass (Figure 2) was removed in toto via careful dissection. A standard carpal tunnel exposure utilizing a longitudinal incision just ulnar to the thenar crease was extended obliquely approximately 2 cm at the distal aspect of the incision at the palm. The mass was removed without difficulty. The longitudinal incision was then utilized to perform the carpal tunnel decompression. The carpal tunnel was decompressed and neurolysis of the median nerve was performed in a standard fashion. The incision was then closed with 4.0 nylon in a horizontal mattress fashion. The tissue sample was sent for histological diagnosis, which confirmed the mass to be a lipoma. No complications appeared post-operatively. The pain, weakness, numbness and hypoesthesia gradually abated during the first month post-operatively with full return to function at the final follow up appointment. 

Discussion  
Lipomas are benign tumors caused by abnormal adipocyte proliferation and are the most common soft tissue tumor encountered (12). Lipomas typically originate in the subcutaneous fat; less frequently, their origin may be submuscular in origin, this includes the muscles of the thenar eminence.  Lipomas can occur in the extremities, and when they do are most frequently present in the proximal extremities.  Lipoma occurrence in the hand is far less common (13). In presentation of lipomas in the hand physical examination may play a more limited role and must be discerned from other common hand masses. The diagnosis of carpal tunnel can be made clinically.  Electromyography (EMG) can be utilized in the diagnosis of carpal tunnel, however it is not required for diagnosis. EMG is often not utilized in patients with classic presenting carpal tunnel, as this patient demonstrated with numbness in the thumb, index, middle and the radial aspect of the ring finger of the right hand and progressive weakness in the thenar musculature.   MRI is the study of choice for evaluation of lipoma. Utilizing MRI, lipoma will appear as a homogenous structure that is the same intensity as fat on all sequences performed (14).  Intramuscular lipomas throughout the body are very rare and form just 1% of lipoma occurrences (15). The constellation of the rare intramuscular lipoma, located in the distal upper extremity, with causation of median neuropathy at the level of the carpal tunnel secondary to increased pressure, makes this case presentation exceedingly rare.  It is the conclusion of the authors that intramuscular lipomas, even when extra-carpal tunnel in location, can result in carpal tunnel syndrome, most likely secondary to increased pressure in the palmar space resulting in increased pressure in the carpal tunnel.  There is an excellent prognosis after excision and carpal tunnel decompression, as demonstrated in this case report. Lipoma, especially in the distal upper extremity, requires a careful diagnostic approach, for which MRI is a useful aid.  

Conclusion 
Intramuscular lipomas, even when extra-carpal tunnel in location, can result in carpal tunnel syndrome, secondary to increased pressure in the palmar space resulting in increased pressure in the carpal tunnel.  Clinical history and a comprehensive physical examination are critical in the diagnosis of carpal tunnel syndrome.  Carpal tunnel decompression and lipoma excision on their own provide an excellent prognosis, when used in combination for treatment of a rare intramuscular lipoma of the thenar musculature, they provide excellent patient recovery and outcomes, as demonstrated by this interesting case.  

Photo/Video 1 | Photo/Video 2

Figure Legend
Figure 1:  T1 and T2 sequence magnetic resonance imaging of the right hand and thumb.  Multiple views demonstrating a 0.7 x 1.9 x 0.7 cm well circumscribed ovoid lesion within the body of the adductor pollicis brevis, isointense to fat on both T1 and T2 sequences.
Figure 2:  Intramuscular lipoma excised in toto found within the body of adductor pollicis brevis  

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