Authors: Christian Kromoser, Stefan Pingitzer, Daniela Mitscha-Märheim, Johann Sellner
Categories: Case Report, Femoral nerve palsy, Hip cyst, Mononeuropathy, Recurrent falls, Musculoskeletal disorder
Source: Neurology and Therapy
Authors: Christian Kromoser, Stefan Pingitzer, Daniela Mitscha-Märheim, Johann Sellner
Synovial cysts originating from the hip joint are rarely symptomatic and are mostly found incidentally by imaging. When the cyst intrudes into the surrounding structures, local pain and swelling, arterial/venous compression, and rarely neurologic symptoms related to disturbance of femoral nerve function can be observed. We report a case of a 78-year-old man who was admitted because of recurrent falls at home over the last weeks. He had been noticing weakness in the right leg, and clinical and neurophysiologic examinations corroborated femoral nerve palsy. A pelvic computed tomography scan depicted a 5-cm-diameter cystic lesion within the right iliopsoas muscle in close contact with the femoral nerve. An ultrasound-guided needle aspiration with evacuation of 5 ml of clear fluid led to a nearly complete resolution of the palsy. We review the available literature on this subject and discuss further differential diagnoses of isolated femoral neuropathy and treatment options for hip joint cysts. Many conditions are associated with falls in older adults. Non-palpable cystic lesions of the hip joint must be considered when clinical examination reveals symptoms of femoral neuropathy. Treatments for symptomatic cysts range from rest, nonsteroidal anti-inflammatory drug administration, and needle aspiration to surgical excision.
Femoral nerve compression by a cystic lesion of the hip is a rare cause of mononeuropathyMany conditions are associated with falls in older adultsNon-palpable cystic lesions of the hip joint must be considered when clinical examination reveals symptoms of femoral neuropathyTreatments for symptomatic cysts range from rest, nonsteroidal anti-inflammatory drug administration, and needle aspiration to surgical excision
Cysts or cystic lesions can develop around any of the joints or tendon sheaths of the body. They may or may not communicate with the adjacent joint. The typical locations of these lesions include the knee, shoulder, and elbow, whereas the hip joint is less frequently affected. Synovial cysts of the hip are commonly associated with degenerative joint disease, rheumatoid arthritis, trauma, and tumors. Notably, soft tissue cystic formations can be divided into ganglionic cysts, synovial cysts, and enlarged bursae. Ganglion cysts do not have a lining of synovial cells and are believed to result from myxomatous tissue degeneration. In contrast, synovial cysts have a lining of synovial cells. They are assumed to develop from herniation of the synovium into the surrounding tissue or displacement of the synovium in the embryonal stage. Bursae are fluid-filled sacs lined by synovial membranes, which provide a cushion between bones, tendons, and/or muscles. While the final classification depends on the histologic analysis, these terms are often used interchangeably in the daily clinical routine.
Hip cysts are often asymptomatic and are mostly identified incidentally on imaging examinations. A magnetic resonance imaging (MRI) study of asymptomatic volunteers revealed hip cysts in 13% and a correlation with age and cartilage degeneration [1]. Clinical symptoms include pain, limited joint mobility, and compression of adjacent structures. The latter can lead to bladder and bowel dysfunction, impaired vessel function (external iliac or common femoral artery, femoral or external iliac vein) with subsequent limb edema and peripheral nerve dysfunction (femoral, obturator, or sciatic nerves). Symptomatic cases, however, are rare. There were 25 cases of a synovial cyst of the hip presenting as deep vein thrombosis or painful lower limb swelling in the literature as of 2017 [2]. Reports of femoral nerve compression cases due to a cystic lesion arising from the hip are even less frequent, and a systematic review identified 20 cases up to 2015 [3]. Common symptoms include pain and hypoesthesia in the dermatomes supplied by the femoral nerve and pain elicited by hyperextending, abducting, and internally rotating the hip. The iliopsoas and quadriceps muscles may be weak and accompanied by diminished patellar tendon reflexes.
Fall-related injuries are more common among older persons and are a significant cause of pain, disability, loss of independence, and premature death. The cause of falling in old age is often multifactorial, and identifying the pathomechanism may require a multidisciplinary approach. Major risk factors for falls include impaired balance and unstable gait, polypharmacy, a history of previous falls, visual impairments, cognitive decline, cardiovascular diseases, dizziness, and vertigo, but also environmental factors [7]. Here, we report the case of an older man admitted for repetitive falls, in whom femoral neuropathy secondary to a cystic hip lesion was causal and resolved after ultrasound-guided puncture and drainage of the cyst. We review key clinical features and differential and potential treatment options for the condition.
A 78-year-old white man was admitted to the emergency department of our hospital by his general practitioner because of recurrent falls at home, without loss of consciousness, in the last few weeks. His initial examination took place at the trauma surgery department, where skin excoriation was treated, and fractures were ruled out by x-ray examination. He indicated a reduced right leg extension strength, leading to further evaluation at the neurology department. His medical history included a bilateral neuroforaminal stenosis at L5/S1 and mild heart failure; no medication was taken regularly. Normal daily activities were performed using a walker or with the support of the neighbors during the daytime. The free walking distance before symptom onset was about 5 m, and the walking distance using the walker was about 100 m. The recent fall occurred when he tried to step over the carpet, and he was unable to stand up afterwards.
The examination of muscle strength revealed Medical Research Council (MRC) scores of 4/5 for hip flexion and 3–5 for knee extension on the right side without visible muscle atrophy, corresponding to femoral nerve palsy. The left lower extremity had normal muscle strength. Passive flexion/extension of the right hip was limited to 105/0/10°, respectively. Inward rotation was at 5° and outward rotation at 20°. Knee- and ankle-jerk reflexes of the right side were absent. No pathologic findings of sensibility or blood circulation were present on either side. Secondary to the fall, both knees showed excoriation. Stance was impaired because of weakness of the right leg. There was mild pain within the right inguinal area without a palpable mass.
A computed tomography (CT) scan of the head did not reveal evidence of a recent ischemic or hemorrhagic stroke or traumatic injury of the brain or adjacent structures. MRI of the lumbar spine showed a right-sided neuroforaminal stenosis at the level of L5/S1, degenerative disc disease, and signs of Baastrup syndrome. Laboratory results revealed slightly elevated inflammation parameters at administration without detection of its origin. A chest x-ray excluded pneumonia, and there was no laboratory evidence of urinary tract infection.
Nerve conduction studies (NCS) revealed a reduced amplitude of motor nerve action potential of the right femoral nerve compared to the left side. We detected fasciculations and spontaneous continuous motor unit single discharges (SCMUSDs) in needle electromyographic studies (EMG) of the right vastus medialis muscle, indicating acute neuronal damage. The examinations for the vastus lateralis, adductor magnus, and tibialis anterior muscles were normal. We interpreted these findings as an incomplete lesion of the right femoral nerve.
A subsequent CT of the abdomen with intravenous contrast revealed two hypodense (24 Hounsfield units), semiliquid, and spindle-shaped formations within the right iliopsoas muscle at the level of the inguinal band (Fig. 1). The right external obturator muscle had a third formation of the same quality. A connecting stalk to the hip joint was strongly suspected. Additionally, both hip joints showed severe arthrosis with nearly used-up joint lines and prominent synovial membrane thickening, especially on the right side. No exact entity of the formations could be defined—cystic ganglion-like formation, liquified hematoma, or abscess formation were mentioned as possible correlates.Fig. 1CT scan of the pelvis in different planes showing the biluminal cystic formation. A The two arrows point to the two chambers of the formation within the iliopsoas muscle in frontal plane. A very visible incidental finding was the full urinary bladder. B Transverse plane demonstrating the two chamber-like formation (arrow) and its proximity to the nerve-vessel bundle (*). C Transverse plane showing the belly of the cyst (big arrow) and its supposed stalk (arrowhead↑) in the direction of the hip joint, shaped like an inverted teardrop
Ultrasound-guided aspiration of the cystic formation within the iliopsoas muscle was our primary approach to reduce femoral nerve compression. The ultrasound showed a nearly echo-free elongated formation (diameter 5 × 1 cm) close to the iliopsoas muscle insertion. Ultrasound-guided punction aspirated 5 ml of clear serous liquid, and only slight residual liquid remained within the cavity. There was no bacterial growth upon microbiologic analysis of the liquid. The cyst formation within the obturator muscle was not addressed.
In addition, our patient received intensive physiotherapy focused on regathering strength and coordination for proper gait and better handling of daily activities. Additionally, electrotherapy and ergotherapeutic activities of daily living (ADL) were performed.
He was discharged 7 days after the evacuation of the cyst, which was day 14 since admission to the emergency unit. His strength scores for the right lower limb had fully recovered for hip flexion, extension, and knee flexion. Knee extension was nearly equivalent to the other side at 4+/5. No other sensory or motor deficits were found at the discharge examination. The passive range of motion did not improve to a relevant extent. One week after discharge, strength levels remained stable, and no further hospital administration took place for the next 12 months.
Medical history disclosed recurrent falls, and clinical examination showed femoral neuropathy in the right leg. With confirmation of a right femoral nerve lesion from electrodiagnostic studies, we subsequently conducted an abdominal CT scan to rule out compressing formations. With normal anticoagulation parameters and no anticoagulatory medication, a spontaneous bleeding was unlikely, but there was a chance of hematoma development after the patient's recurrent falls. The abdominal CT scan revealed a cyst at the level of the right hip joint with a supposed connecting stalk. Along with that information, a slight swelling in the right inguinal area was palpable before we decided to carry out ultrasound-guided aspiration of the cyst. We decided against a surgical resection of the cyst because of the patient's age and his already limited general condition. We conducted a first attempt at ultrasound-guided aspiration, and only in case of recurrence would we have considered surgical excision or total hip arthroplasty. Since we did not resect the cyst, a histologically confirmed diagnosis could not be provided. The strength of the right leg extension improved after a puncture and aspiration of cyst fluid. After intense physical therapy, the patient could be dismissed back home 7 days later in good general condition and without signs of recurrence within the following 2 months.
More than half of isolated femoral nerve lesion cases are of iatrogenic origin. Herniorraphy, hip and abdominal surgeries, arterial bypasses, gynecologic operations, and transfemoral angiography are among the most frequent causes. Traumatic injury and fractures of the hip and pelvis or different forms of lacerations account for additional cases [4]. Femoral mononeuropathies can also result from nerve compression by spontaneous or traumatic retroperitoneal hematoma. The incidence ranges from 1.3% to 6.6% of people receiving anticoagulant treatment and 5.5% to 10.4% of people with hemophilia [5]. In contrast, femoral mononeuropathy secondary to a hip cyst is rare. Histology can distinguish two main types of synovial and ganglion. Clinical or radiologic examinations are insufficient for distinguishing the conditions, and subsequent histologic examinations are mandatory for the exact diagnosis. Synovial cysts generally have a lining of synovial cells and can communicate with the adjacent joint. Ganglion cysts are believed to result from myxomatous degeneration of fibrous tissues and rarely communicate with the joint space [4, 6, 7]. Both contain a highly viscous, gelatinous fluid [8]. Ganglion cysts are divided into intra- and extraneural ganglion cysts [9, 10]. A specific entity of synovial cysts is bursal distension. In the hip, the iliopsoas bursa, the largest synovial bursa in the human body, enlarges because of hip diseases that cause inflammation [11].
Independent of their exact histologic entity, hip cysts are rarely symptomatic. They are usually accompanied by hip pathologies such as traumatic injury, rheumatoid arthritis, avascular necrosis of the femoral head, osteoarthritis, or total hip replacement [3, 6]. Cysts with femoral nerve compression are located in the anterior hip and are mostly synovial cysts [3]. The first symptoms may be local pain and compression syndromes of the surrounding nerves and vessels. Of note, other pathologies may have a similar clinical presentation, including psoas abscess, inguinal hernia, iliac hematoma, or aneurysm of the femoral artery [12]. Thus, careful clinical and radiologic examinations are mandatory to confirm the suspicion or exclude differential diagnoses.
Originating from the ventral rami of L2–L4 roots, the femoral nerve descends through the psoas muscle to exit the pelvis into the femoral triangle alongside the femoral artery and vein underneath the inguinal ligament. Its sensory branches innervate the skin of the anteromedial thigh and medial calf. The motoric branches supply the iliacus, sartorius, pectineus, and quadriceps muscles. The anterior rami of L1 to L3 nerves of the lumbar plexus innervate the psoas major muscle [13]. Thus, clinical examination allows a differentiation of mononeuropathy of the femoral nerve and a radiculopathy of the L2–L4 roots. Both conditions feature reduced knee extension, while ankle dorsiflexion is normal in peripheral femoral nerve lesions but is diminished in L2–L4 radiculopathy. Hip adduction is generally unaffected in femoral nerve lesions but not in radiculopathy. Weakness in hip flexion occurs only when the damage to the femoral nerve is localized above the inguinal ligament. Furthermore, mononeuropathy usually causes sensory loss on the anterior but not on the lateral compartment of the thigh, whereas L2–L4 radiculopathy shows impaired sensory function in both areas. The medial thigh and calf are affected in both scenarios. The patellar reflex is reduced or absent, respectively [14]. Some patients with femoral mononeuropathy complain of the inability to climb stairs and walk due to a combination of hip pain and muscle weakness. If significant motor disturbances are in the foreground, patients may not report sensory disturbances.
Standard MRI is the imaging modality of choice to identify and differentiate soft tissue pathologies like hematoma or abscess when searching for the underlying pathology [15–17]. Compared to CT, MRI also provides a higher chance of detecting accompanying joint pathologies or a stalk between a cyst and the adjacent joint because of the higher soft tissue differentiation [18]. While CT can visualize anatomical abnormalities, the sensitivity for the differentiation of tumors, abscesses, and hematomas is limited, in addition to the general disadvantage of radiation exposure [19]. Ultrasound is another option to identify nerve pathologies. It is inexpensive, widely available, and provides high-resolution and dynamic imaging that can be obtained at the point of care. However, limits arise for deep structures, especially when bones overlay the area of interest. Of note, ultrasound is highly observer-dependent and requires experience [20]. Standard MRI can show the outline of a nerve, but distinguishing nerves from similar appearing and surrounding structures can be challenging [20]. High-resolution MR neurography examination is superior to standard MRI to detect and differentiate femoral nerve lesions [21, 22]. Compared to standard MRI studies, MR neurography generates thin sections and high-resolution sequences to optimize visualization of the peripheral nerves. MR neurography is not widely available, thus limiting its utility in clinical practice.
Needle EMG and NCS can corroborate peripheral femoral nerve dysfunction. On EMG, isolated denervation in the quadriceps muscle can indicate mononeuropathy. This examination has no value in the acute phase as these findings are expected 14 days after nerve entrapment. NCS includes sensory studies of the saphenous nerve and motor studies of the femoral nerve, comparing them to the asymptomatic side. Nerve conduction studies can face difficulties when the supposed lesion site is above the inguinal ligament [14, 23, 24].
In general, treatment of entrapment neuropathies is based on removing or reducing the pathology that causes compression. Additional supportive care includes physical therapy, bracing, and orthoses. In approximately two out of three cases, functional improvement is feasible irrespective of the cause of femoral mononeuropathy. The percentage of axonal loss is therefore the most reliable predicting factor, and the chance for favorable outcome is higher when it is < 50% [25]. When a radiologically confirmed hip cyst causes femoral nerve compression, a surgical approach must be considered. An initial conservative treatment may be appropriate in less symptomatic patients. The most common procedures include needle aspiration and open surgical resection. There are also anecdotal reports of successful arthroscopic treatment [26]. Decision making should include the severity of symptoms, the cyst characteristics cyst, other associated hip pathologies, and the individual patient aspects. An initial approach with the less invasive aspiration puncture can be sufficient. However, higher recurrence rates can be expected [27]. Total hip arthroplasty is an appropriate solution in cases of highly degenerative hip joints. Removing the impaired joint as the causative factor of the cyst and resection of the cyst itself during the procedure are further considerations [3].
Our case of femoral nerve compression by a cystic lesion of the hip represents a rare cause of mononeuropathy. Although hip cysts often stay asymptomatic, it is mandatory to include this entity in the spectrum of differential diagnoses of peripheral nerve lesions in the lower extremities, even without other accompanying symptoms. Especially in elderly patients with high rates of hip arthrosis as a causative factor for cysts and recurrent falls without a satisfactory explanation, radiographic examination for hip cysts or other tumor-like formations is mandatory. MRI is regarded as the superior modality to depict nerve lesions or soft tissue formations, but when necessary, a CT scan is a reliable alternative to obtain a quick and sufficient overview of possible nerve-compressing pathologies.