Spinner, Robert J.

Patients with traumatic brachial plexus injuries (TBPI) undergo clinical examination and electromyography (EMG) to characterize injury severity and localization. However, precise localization with EMG alone can be difficult when multiple injury sites are possible. Brachial plexus ultrasound (BPUS) allows direct visualization of the brachial plexus, a needed adjunct to EMG to reveal multiple sites of injury in TBPI. We summarize three cases of EMG-confirmed upper trunk TBPI which were clarified using BPUS to additionally involve electrically hidden injuries to the extraforaminal C5 and C6 nerve roots. BPUS demonstrated extensive scarring and focal enlargement of the upper trunk in each patient (all cross-sectional area [CSA] ≥24 mm 2 ). However, all patients also had C5 and C6 extraforaminal nerve root enlargement (all CSA ≥9 mm 2 and 12 mm 2 , respectively), revealing further neural involvement proximal to the upper trunk into the EMG “gray zone”– postganglionic, extraforaminal cervical nerve root injury which is clinically and electrodiagnostically indistinguishable from the plexus but anatomically and radiographically distinguishable on BPUS. Some EMG-identified upper trunk TBPI may have more proximal involvement of the contributing extraforaminal C5-6 nerve roots, an area electrically indistinguishable from an upper trunk TBPI without the assistance of advanced imaging.

BACKGROUND Neurolymphomatosis (NL), characterized by lymphoma infiltration of peripheral nerves, can be diagnostically challenging because of nonspecific clinical presentations and imaging findings. Tumefactive NL refers to circumferential subparaneurial tumor deposition beneath the paraneurium, outside the epineurium, producing an “encased” nerve appearance on MRI and at surgery. OBSERVATIONS A 76‑year‑old man with treated large B‑cell lymphoma developed a painful left lower trunk brachial plexopathy with numbness of the ring and little fingers and progressive weakness in finger flexors and intrinsic hand muscles. Serial brachial plexus MRI and 18F-fluorodeoxyglucose positron emission tomography over 4 months demonstrated evolution from a thin, circumferential subparaneurial rim of enhancement with mild nerve enlargement to a homogeneously enhancing, tumefactive lesion of the C8 nerve root and lower trunk. Targeted fascicular biopsy of a nonfunctioning C8 fascicle confirmed recurrent B‑cell lymphoma. LESSONS This case illustrates temporal evolution along the tumefactive NL spectrum, from early, subtle subparaneurial involvement to a frankly tumefactive lesion. Recognizing this early MRI pattern, particularly in patients with a history of lymphoma and focal plexopathy, can guide targeted biopsy and facilitate earlier diagnosis and treatment. The clinicoradiological findings suggest that subtle peripheral/subparaneurial enhancement may precede overt tumefactive enlargement. https://thejns.org/doi/10.3171/CASE26139

BACKGROUND Differential awakening is a well-known, yet poorly understood phenomenon seen in patients with intracranial pathologies. Because acute postoperative neurological decline has many potentially reversible causes, distinguishing differential awakening from other etiologies is critical. To the authors’ knowledge, differential awakening has not been reported following peripheral nerve procedures. OBSERVATIONS A 40-year-old man presented with a 1.5-year history of painful bilateral cervical and right lumbosacral radiculoplexus neuropathy recently associated with bilateral facial and vestibulocochlear neuropathy. He had not responded to treatment trials. A sciatic nerve lesion in the sciatic notch was identified on imaging and an open biopsy of the posterior femoral cutaneous nerve was pursued. Immediately after emergence from anesthesia, he demonstrated a complete inability to dorsiflex or plantar flex the right foot, despite minimal intraoperative manipulation of the sciatic nerve. Over the ensuing hour, motor function progressively returned to baseline. The transient postoperative motor deficit was attributed to differential awakening of the sciatic nerve. Pathological analysis confirmed high-grade B-cell lymphoma. LESSONS Differential awakening may be an underrecognized cause of transient neurological worsening during emergence from anesthesia following peripheral nerve surgery. Further investigation is needed to clarify the underlying mechanisms and define its incidence and risk factors. https://thejns.org/doi/10.3171/CASE251028

Despite advances in imaging, instrumentation, surgical techniques, and postoperative care, outcomes for certain peripheral nerve procedures remain consistently disappointing. In this article, we describe five surgical scenarios--adult pan-brachial plexus injuries, peroneal nerve injury after knee dislocation, sciatic nerve injury after total hip arthroplasty, radiation-induced brachial plexopathy, and lower trunk injury after cardiac surgery--that, in our experience and review of the literature, frequently lead to limited and consistently poor functional recovery after nerve surgery. These challenging cases reflect not only technical and anatomical complexity but the profound biological limitations of nerve regeneration in specific contexts. By critically analyzing these five procedures, we aim to promote more realistic patient counseling, support timely and individualized decision-making, and foster a more nuanced understanding of when and what type of surgical intervention may or may not be beneficial.

BACKGROUND AND OBJECTIVES: Intraneural ganglion cysts (IGCs) can arise in different nerves but are uncommon in the tibial nerve (TN) and its branches near the ankle. According to the unified articular theory, a joint connection is always present in IGCs. This study aimed to identify joint connections of tibial-region IGCs and characterize their clinical, radiological, and propagation patterns. METHODS: A prospectively collected international database of >1100 IGCs was reviewed to identify tibial and medial plantar nerve (MPN) and lateral plantar nerve (LPN) IGCs around the ankle. RESULTS: Sixty-two ankle region IGCs were identified: 29 involving the TN (46.8%), 25 the MPN (40.3%), and 4 the LPN (6.4%); in 4 cases, the parent nerve was indeterminate. Thirty-one (50%) cases demonstrated joint connections. Of these, all TN at/distal to the tarsal tunnel (n = 4/4, 100%), MPN (n = 16/16, 100%) and LPN IGCs (n = 2/2, 100%) had a connection to the subtalar (ST) joint. A tibial IGC just proximal to the tarsal tunnel was connected to the tibiotalar (TT) joint in 75% of cases (n = 3/4) and the ST joint in 25% of cases (n = 1/4). Surgical ligation/disconnection of the articular branch was associated with markedly lower recurrence (0/13, 0%) compared with incision or resection of cyst without ligation (8/29, 27.6%; P = .04). CONCLUSION: Our findings support the unified articular theory. All IGCs in the ankle primarily ascend. Two distinct propagation patterns emerged: (1) those that ascend and enter the parent nerve proximal to the tarsal tunnel continue to ascend in the leg, without affecting the plantar nerves, and (2) those that ascend and enter the parent nerve at/distal to the tarsal tunnel have the potential to undergo crossover at the TN bifurcation and subsequently descend down the plantar nerves seen only in ST-origin cysts. Recognizing these pathways enhances diagnostic accuracy, directs identification of the joint of origin, and guides articular branch disconnection to reduce recurrence.

OBJECTIVE Neuromuscular choristoma (NMC) is a rare developmental lesion that may give rise to desmoid-type fibromatosis (DTF) within the same nerve territory (NMC-DTF). While MRI features of NMC are well established, the natural history of progression to NMC-DTF has not been systematically described. This study aimed to define radiological groups from NMC to NMC-DTF using serial MRI and a literature review. METHODS Following IRB approval, the authors retrospectively analyzed 28 patients with NMC from their institutional database. Diagnosis was based on pathology or classic clinicoradiological features. Sequential MR images were reviewed to evaluate nerve enlargement, enhancement patterns, low T1/T2 foci, and NMC-DTF formation. Cases were classified into 3 radiological groups: 1) classic NMC with typical MRI features (group I), 2) NMC plus, with atypical features (foci of low T1/T2 signal intensity and/or at least moderate postcontrast enhancement; group II), and 3) NMC-DTF with a mass outside of the epineurium (group III). Data were correlated with pathology results and prior reports from the literature. RESULTS Of the 28 patients, 24 underwent serial MRI. Eleven patients presented with group I features, 4 with group II, and 9 with group III. Among group I patients with follow-up imaging, 4 (36.4%) progressed to group III over a mean of 6.2 years and 1 (9.1%) to group II. All 4 group II patients (100%) developed NMC-DTF within a mean of 3.0 years. All group III patients demonstrated NMC-DTF extending beyond the epineurium. No prior cases in the literature documented radiological progression from NMC to NMC-DTF on serial MR images. CONCLUSIONS The authors propose a framework for NMC progression based on radiological features, identifying group II as being high risk and a potential transitional phase for the formation of DTF. Structured surveillance with serial MRI is essential to prevent iatrogenic triggers and improve management strategies in patients with NMC.

BACKGROUND Perineural spread (PNS) of colorectal carcinoma (CRC) is a rare and challenging diagnosis. Its clinical and radiological presentation is often subtle and can overlap with radiation-induced neuropathy and malignant nerve tumors, complicating timely diagnosis. The role of circulating tumor DNA (ctDNA) in the detection of PNS has not been previously described. OBSERVATIONS A 48-year-old man with a history of rectal cancer and perineural invasion presented with progressive, refractory sciatic neuropathic pain. Conventional surveillance imaging was initially negative despite subtle rising of carcinoembryonic antigen and ctDNA levels. Subsequent MRI revealed abnormalities of the lumbosacral plexus and sciatic nerve, and fascicular biopsy confirmed metastatic CRC involving the sciatic nerve, establishing the diagnosis of PNS. LESSONS This case highlights PNS as a rare but important consideration in patients with focal neuropathic symptoms and prior CRC. Circulating tumor DNA positivity may serve as an early indicator of occult tumor activity even within the nerves when imaging is equivocal. However, currently histopathological confirmation remains the only definitive method to distinguish PNS from alternative diagnoses and is essential to guide appropriate management. https://thejns.org/doi/10.3171/CASE25997

BACKGROUND Bertolotti syndrome is an underrecognized cause of chronic low back pain. Back pain generated from Bertolotti syndrome is believed to result from altered weight dissipation mechanics and/or instability of the pseudoarticulation, while local nerve root compression may result in radiculopathy. Here, the authors describe the findings of a patient with treatment-refractory low back pain found to have a cystic lesion arising from a Bertolotti joint causing L5 nerve root compression. To their knowledge, this has not been previously described in the literature. OBSERVATIONS Despite early recognition of Bertolotti syndrome, the patient’s back pain remained resistant to many years of both conservative and surgical management. The novel finding of a cyst arising from the pseudoarticulation complicated the management. The patient is scheduled to undergo further surgery this year. LESSONS This case highlights a pseudocyst associated with a Bertolotti joint. The cyst introduced additional clinical uncertainty to what is already an uncommon and difficult to treat condition. Resection of the Bertolotti joint failed to improve the patient’s symptoms. Postoperatively, a complex hemorrhagic pseudocyst was seen on imaging, possibly due to the pseudoarticulation with persistent motion. Ongoing efforts to characterize Bertolotti syndrome and its associated imaging findings are necessary to better optimize management strategies in these patients. https://thejns.org/doi/10.3171/CASE25948

BACKGROUND Intraneural ganglion cysts (IGCs) are mucinous lesions that originate from adjacent synovial joints. According to the articular theory, synovial fluid tracks from a joint into the parent nerve through an articular branch. In uncommon sites such as the sural nerve, this connection can be difficult to identify. This report illustrates the use of a preoperative intra-articular fluorescein injection as a tool to identify the articular branch during surgery. OBSERVATIONS A 60-year-old woman presented with lateral foot pain, numbness, and a palpable mass along the left sural distribution. MRI showed a large cyst extending along the course of the sural nerve with connection to the subtalar joint. Fluorescein was injected preoperatively into this joint to detect the articular branch intraoperatively with ultraviolet illumination. The connection was transected at the joint origin, and the cyst was decompressed, preserving the parent nerve. Postoperatively, the patient had complete pain relief and sensory recovery, and MRI at 3 and 8 months confirmed resolution of the cyst. LESSONS Sural IGCs conform to the articular theory and can be managed effectively by transection of the articular branch. Preoperative intra-articular fluorescein injection is a useful tool to detect the articular branch that can be difficult to find in sural IGCs. https://thejns.org/doi/10.3171/CASE251018