Turret exostosis is an uncommon benign osteocartilaginous lesion arising from the cortical surface of bone and most frequently involving the phalanges of the hand. It is believed to represent a reactive subperiosteal ossification that occurs following minor or repetitive trauma to the digits ^[1,2]. Patients typically present with a gradually growing firm swelling over the finger, which may be accompanied by stiffness, pain, or limitation of joint mobility, depending upon the extent and location of the lesion. Radiographically, turret exostosis typically appears as a well-defined ossified mass arising from the cortical surface of bone without continuity with the medullary canal. This feature helps differentiate it from conventional osteochondroma ^[3]. However, the clinical and radiological findings may overlap with other periosteal lesions such as periosteal chondroma and bizarre parosteal osteochondromatous proliferation (BPOP), commonly referred to as Nora’s lesion ^[4,5]. Therefore, histopathological examination is essential for establishing the definitive diagnosis. Most reported cases involve the distal or middle phalanges of the hand, whereas involvement of the proximal phalanx is relatively rare ^[1,6]. Due to its rarity and potential for misdiagnosis, awareness of this entity is important for appropriate management. Complete surgical excision is the preferred treatment, with excellent functional results and a low chance of recurrence ^[1,6]. We present a rare case of turret exostosis arising from the proximal phalanx of the middle finger and discuss its clinical features, radiological findings, surgical management, and histopathological characteristics.

Patient information: 

A 32-year-old male patient who predominantly used his right hand presented with a progressively growing swelling on the dorsal part of his right middle finger’s proximal phalanx (Fig. 1). There were no noteworthy comorbidities or prior medical history for the patient.

History of present illness: 

The swelling had been present for approximately 1 year and was initially painless. Pain developed about 4 months after the onset of swelling and gradually increased in intensity. The pain was aggravated by finger movements. The patient reported a history of trivial trauma to the affected finger approximately 1 year before presentation. Mild restriction of flexion at the proximal interphalangeal (PIP) joint was noted.

Clinical examination: 

On examination, a firm, non-mobile swelling measuring approximately 2 × 1 cm was present over the dorsal surface of the proximal phalanx of the right middle finger. The lesion was tender on palpation. There were no visible signs of inflammation, and the skin above seemed normal. Mild restriction of PIP joint flexion was observed, whereas extension was preserved. Neurovascular examination of the finger was normal.

Investigations: 

Plain radiographs of the hand (anteroposterior and oblique views) demonstrated a well-defined ossified lesion arising from the cortical surface of the proximal phalanx without continuity with the medullary canal (Fig. 2). Magnetic resonance imaging (MRI) showed a surface-based osteocartilaginous lesion with a thin cartilage cap and no intramedullary extension (Fig. 3). Based on these findings, the differential diagnoses included turret exostosis, osteochondroma ^[3], periosteal chondroma, and BPOP ^[4,5].

Treatment: 

Surgical excision of the lesion was performed under regional anaesthesia. Intraoperatively, a well-circumscribed bony mass that measured approximately 2 × 1 cm was identified arising from the dorsal cortex of the proximal phalanx. The lesion was completely excised along with its base (Fig. 4). There was no involvement of the extensor tendon or surrounding soft tissues. Post-operative radiographs confirmed complete removal of the lesion (Fig. 5).

Histopathological findings:

The diagnosis of turret exostosis was confirmed by histopathological analysis, which demonstrated a cartilage cap made of mature hyaline cartilage with fibrous perichondrium and underlying mature trabecular bone ^[2].

Follow-up and outcome: 

The post-operative period was uneventful. At 3-month follow-up, the patient demonstrated good finger mobility. The patient showed no signs of recurrence at the 1-year follow-up, and both the proximal and distal interphalangeal joints had a full range of motion (Fig. 6 and 7).

Turret exostosis is a rare benign osteocartilaginous lesion believed to arise from ossification of a subperiosteal haematoma following trauma ^[1]. Most frequently, the hand’s phalanges are affected, particularly the distal and middle phalanges, whereas involvement of the proximal phalanx is relatively uncommon ^[1,6]. The literature has also included a number of case reports detailing turret exostosis affecting various digits and anatomical locations ^[7,8,9,10]. The presence of preceding trauma in our patient further supports the reactive nature of this lesion. A distinct ossified mass that emerges from the cortical surface of the bones, lacking corticomedullary continuity, is the radiographic hallmark of turret exostosis, which helps distinguish it from conventional osteochondroma ^[3]. MRI is helpful in evaluating the cartilage cap and ruling out intramedullary extension. An important differential diagnosis is BPOP, also known as Nora’s lesion, which typically demonstrates more aggressive growth and has a higher recurrence rate following excision ^[4,5]. Distinguishing between these entities may be challenging on imaging alone, making histopathological examination crucial for definitive diagnosis. Turret exostosis is still best treated with complete surgical excision. Adequate removal of the lesion along with its base reduces the risk of recurrence and restores normal finger function ^[1,6]. In the present case, complete excision resulted in excellent functional recovery with no recurrence during 1 year of follow-up.

Turret exostosis is an uncommon benign osteocartilaginous lesion that may develop following minor trauma and can present as a dorsal finger swelling. Because its clinical and radiological features may mimic other periosteal lesions, accurate diagnosis requires careful clinicoradiological assessment and histopathological confirmation. Complete surgical excision results in excellent functional recovery with minimal recurrence.

A slowly enlarging dorsal finger swelling following trauma should prompt consideration of turret exostosis in the differential diagnosis. Awareness of this entity and timely surgical excision after appropriate imaging can prevent diagnostic confusion and ensure good functional recovery.