A giant synovial cyst in combination with the ‘congenital insensitivity to pain’ syndrome

S. Kroeze1

T. de Windt2 C. Vogely2 F.C. Oner2 1Utrecht University, The Netherlands 2Universitair Medisch Centrum Utrecht, The Netherlands


A 36-year old patient with congenital insensitivity to pain (CIP) syndrome, presented with severe swelling of the left thigh several weeks after a mild knee trauma. Radiological examination excluded a femoral fracture. CT and MRI identified multiple large cysts, which surrounded the proximal femur and extended to the ankle. Treatment consisted of surgical exploration and drainage followed by extensive microscopic and pathological examination. Based on both imaging and pathological analysis, a giant synovial cyst was diagnosed in this CIP patient. Because of the inability to feel pain or discomfort, CIP patients may show patient-delay. This case justifies the need for strict follow-up for CIP patients suffering from (mild) trauma, in order to detect complications in an early stage.

Introduction The congenital insensitivity to pain (CIP) syndrome or hereditary sensory and autonomous neuropathy (HSAN), is a rare disease with an estimated incidence of 1 in 25.000.1,2 CIP was first described in 1963 by Swanson.3 CIP syndrome has an autosomal recessive inheritance pattern and is genetically and clinically heterogeneous. The disease is characterized by an inability to feel pain from any stimulus, including inflammation and heat, whether or not accompanied by autonomous disorders. Sensibility, vibration, sense of position, motor skills, and tendon reflexes are intact. As a result, a CIP patient is able to distinguish hot and cold, but lacks the ability to detect a (dangerously) hot object.4,5 Because of the inability to experience pain, a CIP patient may be less likely to consult a doctor. This could lead to patient-delay causing uncommon and extraordinary presentations, like in the case presented here.

Patient The patient is a 36-year old female with Moroccan, born in the Netherlands and raised in a family of seven children (three girls and four boys). They all have the same parents, who were cousins. Besides CIP, no further family history was known. CIP was present in one additional sibling. The patient’s medical history includes multiple fractures, including femoral- and hip fractures, resulting in a left resection arthroplasty (Girdlestone situation). In addition, the patient suffers from a Charcot foot, with failed arthrodesis based on recurrent infections.

Intervention The patient presented with severe swelling of the left thigh several weeks after a mild trauma. She did not suffer from pain or any other complaints and was still able to bear weight on the affected leg. Physical examination showed an adequate female, with a body mass index (BMI) of 27.8, and blood pressure, pulse, and temperature within normal ranges. Inspection showed an evident swelling of the upper leg, mainly located in the left groin, in the genital area, and over the left buttock and upper thigh. No clear signs of knee-effusion were seen. Motor- and sensory functions were intact and symmetrical. Conventional X-rays showed no fracture and no cranialization of the proximal femur in relation to previous examinations (figure 1). Ultrasound of the swelling on the medial side of the thigh revealed multiple hypo-echoic inhomogeneous collections. The computed tomography (CT) showed the intramedullary pin fixation on the proximal side of the right femur and a Girdlestone of the left femur.

Figure 1. AP X-ray of the pelvis and proximal femur showing a past resection arthroplasty (Girdlestone) of the left proximal femur and intramedullary pin fixation of the proximal right femur. There were no new fractures found and no cranialization of the proximal femur was seen compared to previous exams.

Furthermore, multiple fluid collections with marginal colouring were seen in the left hip, gluteal region and thigh, with soft tissue induration surrounding the left hip (figure 2a). Repeated Magnetic Resonance Imaging (MRI) with a three-week interval showed an increase in size of the lesions, with extension of the intermuscular fluid collection from the pelvis to the lower extremity. The second MRI showed two large cysts anteriorly and posteriorly in the gluteal region of 7.0 x 2.8 x 4.5 cm and 11 x 3.0 x 7.1 cm, respectively. The largest cyst was found in the hamstring region with the greatest dimensions of 20 x 6.4 x 3.6 cm, and an extension to the achilles tendon (figure 2b).

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Figure 2.a

Figure 2a and 2b. Coronal CT (figure 2a) and MRI (figure 2b) showing multiple fluid collections in the left hip and thigh with marginal colouring and induration in the soft tissue surrounding the hip. Arrows indicate the largest cysts seen on the MRI both gluteal and extending from the hamstrings to the ankle (figure 2b).

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Figure 2.b

Ultrasound and MRI were not indicative of a Morel Lavallee lesion as the giant cyst had an intermuscular and intercompartimental orientation and a normal relation between the skin, subcutaneous fatty tissue and the underlying fascia was seen. Laboratory tests showed a c-reactive protein (CRP) of 1 mg/L, an erythrocyte sedimentation rate (ESR) of 4 mm/hour, and a haemoglobin level of 7.7 mmol/L. The ultrasound guided aspiration of the fluid collections (450ml serosanguinolent fluid) were sent for pathological and microbiological assessment. Due to a further increase of the swelling within several days of admission, which now ranged from the thigh to the ankle, the patient underwent surgical exploration and drainage. Three drains were placed near the proximal femur and thigh. The patient was treated with broad-spectrum antibiotics (Cefacidal 4 x 1g intravenous). A pressure bandage was applied around the entire left leg. Culture assessment was conducted for pathogenic micro-organisms, yeasts and fungi, leukocyte counting, and crystals; all tests were negative. Pathological examination of the cyst tissue showed synovial tissue with reactive changes. Besides, avital bone was seen with some reactive changes and signs of inflammation, matching osteomyelitis.

Comparison Since CIP syndrome is a rare disease, and a giant synovial cyst an uncommon diagnosis, it is difficult to compare the diagnostic and therapeutic modalities to literature. For detection of cystic lesions, MRI is superior to all other imaging modalities.6,7 However, because MRI lacks the ability to detect subtle areas of matrix mineralization we chose to add a CT scan as a diagnostic modality. Since CT is able to detect subtle abnormalities, which may occur as a result of ossification or calcification, CT has additional value to MRI. The morphologic characteristics of these subtle areas of mineralization may aid in de diagnostic process of soft tissue masses. 7,8 Moreover, the use of 3D imaging with CT may allow a better understanding of the anatomic relationship between the soft tissue mass and adjacent neurovascular and osseous structures. This can be of considerable value in designing an optimal surgical approach.8

Outcome During the first four days after surgery, the drains produced a total of 1680ml serosanguinolent fluid. The drains were removed after five days because of diminished production. Exudate from the wound was seen until day eleven post-surgery. Afterwards, no recurrence of swelling was seen. The patient was allowed partial weightbearing for three weeks. She returned for follow-up after 6 weeks, three- and nine months. At the final follow-up, the patient had no clinical symptoms of discomfort, the wound remained dry and no signs of recurrence were shown.

Comparing the literature Cysts of the hip and knee can appear incidentally, but are usually accompanied by hip disorders such as trauma, avascular necrosis of the femoral head, osteoarthritis, rheumatoid arthritis, and total hip arthroplasty.6,9,10 The preferred orientation of synovial cysts are around the knee where they often arise between the tendons of the medial head of the gastrocnemius and the semimembranosus muscles (Baker’s cyst).9 Commonly, these patients present with pain, discomfort, swelling in the popliteal space, and/or a decreased range of motion.9,11 Symptoms that our patient was unable to experience. To the best of our knowledge, no ‘giant’ synovial cyst has been described previously that ranges from the pelvis to the ankle, whether or not in the CIP syndrome.

Recommendation Patients with CIP syndrome are unable to experience pain, which can lead to patient-delays and unusual clinical presentations. Indeed, a strict follow up regime after trauma in CIP patients is warranted, to avoid complications at an early stage. A physician should be aware of an uncommon presentation in CIP patients and has to inform them about the risk of patient-delay. Furthermore, both CT and MRI, can play an important role in the diagnostic process of rare (‘giant’) cysts.

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