Malignant Fibrohisticytoma of the Knee in a Patient with HIV
The patient WPO, from the city of São Paulo (Brazil), a 75-year-old caucasian male, had been receiving antiretroviral treatment in Hospital das Clínicas of São Paulo, since being diagnosed with HIV 12 years earlier (now taking lamivudine, tenofovir, atazanavir, and ritonavir for the last three years). He was in a good general condition, with good viral and immunological control (undetectable viral load and CD4 count of 653/mL). He also had lipodystrophy syndrome diagnosed five years ago. Other laboratory tests were normal, and he did not have any other coinfections, had no drug addiction, and no other comorbidities.\nHe sought medical assistance because of a complaint of patellofemoral pain in his right knee that had started one year earlier with increasing local volume and progressive inability to perform active extension. He had a knee extension lag of 30°. He was able to walk only with a stick. The increased volume was concentrated below the patella and posterior to the patellar tendon, without local inflammatory signs, history of trauma, and infection.\nThe initial suspicion was inflammatory abnormalities of Hoffa's fat pad. In addition, a tendinopathy with partial chronic lesion of the patellar tendon probably explained the clinical findings.\nIt was decided first to perform a magnetic resonance imaging (MRI) [Figures and ]. This revealed the presence of edema and thickening of the infrapatellar fat, with the formation of a nodule measuring 2.0×1.6×2.0 cm, with low signal and no impregnation with contrast. This was interpreted as a solid fibrous mass. The patellar tendon was found thickened, with foci of partial ruptures and with peritendinous edema.\nThe treatment for this situation is essentially nonsurgical. Since our patient did not show any improvement through physiotherapy and drug treatment, surgical treatment was indicated. This was done with the aim of exploring the patellar tendon and reconstructing it if necessary, along with partial resection of Hoffa's fat and the nodule, with pathological analysis of the tissue.\nThe intraoperative appearance of the knee showed an intact patellar tendon with an infiltrated tissue around Hoffa's fat, without any local inflammatory reaction []. It was decided only to biopsy this tissue and culture for bacteria, mycobacteria, and fungi.\nNone of the cultures was positive. On the 14th day after the operation, the results from the anatomopathological examination revealed that the nodule consisted of a high-grade malignant fibrohistiocytoma, without sufficient margins of resection.\nAfter ruling out metastasis [by thoracic and abdomen computed tomography (CT) and bone scintigraphy], our patient underwent bloc resection of the entire joint, including the distal femur, proximal tibia, patella, and musculature of the distal quadriceps.\nThe knee joint was reconstructed using an endoprosthesis, which was covered by rotating a flap from the medial gastrocnemius muscle and the extensor mechanism was reconstructed using the sartorius muscle. The pathological analysis confirmed free resection margins.\nThe patient has a good functional outcome, walking with the aid of one crutch and without any recidive after 18 months of the surgery.