Working Diagnosis:
Schwannoma of the left tibial nerve, left chondromalacia, and a partial thickness tear of the left medial gastrocnemius tendon

Treatment:
The patient followed up with us post-op, and her left chondromalacia and partial tear of the left gastrocnemius were managed conservatively. This management included the use of the PTO Tru-Pull Lite brace, activity modification, referral to formal physical therapy for 6 weeks, and the use of NSAIDs as needed for pain control.

Outcome:
Four months later, she returned to the clinic for her most recent follow-up visit, and her retro-patellar knee pain had significantly improved. She was recommended to continue working on strengthening and then progress to sport-specific activities, followed by a return-to-running program. Additionally, she was advised to wear orthotics and to follow up with us if any issues arise.

Author's Comments:
Schwannomas, also known as neurilemmomas, are benign peripheral nerve sheath tumors composed of Schwann cells, comprising only 5% of all soft tissue tumors. Magnetic resonance imaging (MRI) is considered the most advantageous imaging modality for diagnosing schwannoma. However, definitive diagnosis is done with a surgical biopsy of the mass. Asymptomatic cases typically receive conservative treatment, which involves periodic monitoring of the tumor with MRI, while surgical resection is performed for symptomatic or rapidly growing tumors. In cases of malignant schwannomas, a combination of radiation therapy and surgery may be utilized.

Editor's Comments:
The key clinical clues in this case are the palpable mass on exam and presence of reproducible paresthesias in the foot. Otherwise, medial joint line tenderness and mechanical symptoms would lead you down the path of meniscal pathology. The differential for a popliteal mass can range from a benign Baker’s cyst to a malignant tumor or vascular lesion such as a popliteal artery aneurysm. Ultrasound can be utilized as an initial study to determine whether the mass is cystic, solid, or vascular, and whether it is intra-articular or extraarticular. MRI and subsequent biopsy are indicated for all masses that are not clearly benign (popliteal cysts or lipoma) or vascular.

References:
1. Schwannoma. Johns Hopkins Medicine. (2022, March 10). https://www.hopkinsmedicine.org/health/conditions-and-diseases/nerve-sheath-tumor/schwannoma
2. Salunke AA, Chen Y, Tan JH, Chen X, Foo TL, Gartner LE, Puhaindran ME. Intramuscular schwannoma: clinical and magnetic resonance imaging features. Singapore Med J. 2015 Oct;56(10):555-7. doi: 10.11622/smedj.2015151. PMID: 26512147; PMCID: PMC4613930.
3. Chalilk , N, Frydenberg, E, Henry, S, Higgs, A, & Steel, T. (2019, July 8). Schwannoma of the tibial nerve–an unusual case of Foot Pain. Interdisciplinary Neurosurgery. https://www.sciencedirect.com/science/article/pii/S2214751919300581
4. Mahajan M, Sharma R, Sharma P, Gupta A Schwannoma of Superficial Peroneal Nerve Presenting as Leg Pain.JCR 2012;2:79-82
5. Cherrqi A, El Haddad S, Messaoud O, et al. Saphenous Nerve Schwannoma: A Rare Differential Diagnosis of Knee Pain in Children. Global Pediatric Health. 2023;10. doi:10.1177/2333794X231156047
6. Kapoor, Rajat, and Bharat Rajivkumar Saxena. “Case series of peripheral nerve sheath tumours: Schwannoma.” JOURNAL OF CLINICAL AND DIAGNOSTIC RESEARCH, vol. 12, no. 9, 2018, https://doi.org/10.7860/jcdr/2018/35340.11973.
7. Schweitzer KM, Adams SB, Nunley JA. Multiple Schwannomas of the Posterior Tibial Nerve: A Case Series. Foot & Ankle International. 2013;34(4):607-611. doi:10.1177/1071100712470916
8. Hao, X, Levine, D, Yim, J, Qi, C, Firestone, L, Beiser, I, Leone, E, Woelffer, K, & Mirkin, G. (2019, September 1). Schwannoma of Foot and ankle: Seven case reports and literature review. Anticancer Research. https://ar.iiarjournals.org/content/39/9/5185

Acknowledgments:
Junior Editor: Rahul Kapur, MD

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