A 44-year-old woman came to our clinic with an asymptomatic slowly progressive swelling over her upper back. She first noticed the swelling incidentally, small as a lemon, about four years ago. Her medical history was unremarkable, and she did not have any sensory or motor changes. Clinical examination revealed a spherical non-tender swelling in the paraspinal area over the upper back, sized 7.0x6.5 cm [Figure 1A]. Fluctuation was present on palpation, but thrill was absent. There were no other associated symptoms and no tenderness on spinal palpation. MRI revealed a well-defined, smooth-margin, oval-shaped swelling in the superficial-intermuscular plane. It lay underneath the trapezius, displacing the rhomboid and serratus posterior superior, and was superficial to the erector spinae muscles [Figures 2A,2B]. While extending deep and medially towards the right side of the spinous process, it stayed far-off the dorsal spinal rami. There was a clear-cut plane between the cyst and surrounding muscles, with no local invasion [Figures 2C,2D]. Relationship with any identifiable nerve was absent, nor was it related to any nerve course. Central part appeared necrotic with blood-fluid levels, with calcifications in the wall [Figure 2A,2C]. Contrast-enhanced T1-weighted images showed ring-like capsular enhancement [Figures 2B,2D]. Ultrasound-guided FNAC was performed, but the results were inconclusive. The pre-operative diagnosis was that of a benign, purely-cystic, superficial, inter-muscular, extra-spinal swelling. The patient was scheduled for surgical excisional biopsy.
After surgical exploration, incising the fascia and retracting the trapezius helped reach the cystic swelling underneath, covered with a glistening whitish-grey capsule [Figure 1B]. It extended inferiorly and medially deep towards the spine, displacing the rhomboid and serratus posterior superior. Lying superficial to the erector spinae muscles, it extended towards the right spinous processes of upper thoracic vertebrae, but far-off from the spine or spinous ligaments [Figure 3A]. Dissection proceeded effortlessly through a well-defined plane between the swelling and the surrounding muscles. While a fascial pedicle attached its base to the underlying soft tissues, it was not adherent to any surrounding nerves. After complete surgical excision, the resulting wound was reconstructed in layers from deep to superficial. Gross examination of the specimen revealed a cystic swelling sized 6.5x5.0x2.5 cm [Figure 3B]. The cut-section contained dark reddish-brown areas, signifying haemorrhagic changes inside. An encapsulated lesion with hyper and hypocellular areas was seen on histopathological examination. Cystic degeneration was present in the centre [Figure 4A]. Bland oval to spindle-shaped cells was present. Hypercellular areas with nuclear palisading (oval-shaped Verocay bodies) were noted. Neither nuclear atypia nor increased mitotic activity was visible [Figure 4B]. Immunohistochemistry was strongly positive for S-100, and negative for CD34, Cytokeratin-Pan (AE1/AE3), Smooth muscle actin, with Mib1 of 1% [Figure 4C]. Final diagnosis confirmed benign cystic schwannoma. Recovery during the postoperative period was uneventful, and the wound healed well with minimal scarring. There were no recurrences or other complications during the next one-and-half-year follow-up period.